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Quark Matter 2012
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US/Eastern
John William Harris
(Yale University (US))
Description
The Quark Matter series of conferences aims to reunite international specialists in the field of experimental and theoretical heavy ion physics.
This fundamental research consists of studying excited matter at the subatomic level to understand how the constituents dynamically arrange themselves to form ordinary matter, and to understand how this organization emerged from the primordial matter created by the Big Bang at the beginning of the universe.
The Quark Matter 2012 conference is the twenty-third edition of this prestigious series of international conferences organized approximately every 18 months since 1982. Recent instances of the conference have taken place in Shanghai, China (2006), Jaipur, India (2008), Knoxville, USA (2009). and Annecy, France (2011).
Please Note:
- Student day will take place on Sunday, August 12, 2012
- Nuclear Physics A will be sponsoring a NPA Young Scientist Award at QM'12
If you have any questions about the details of the program please contact Bolek Wyslouch
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09:00
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12:30
Student's Day A (Chair S. Bass) Palladian
Palladian
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10:00
Coffee Break 30m Bird Cage
Bird Cage
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12:30
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13:30
Student Lunch 1h
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13:00
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15:30
Teacher's Day Empire
Empire
- 13:00
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15:15
Break 15m
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16:30
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17:15
Student and Teacher Reception 45m
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17:15
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22:00
Conference Registration
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09:00
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12:30
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07:30
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Conference Registration (All day)
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10:15
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10:45
Coffee Break 30m Bird Cage & Regency Gallery
Bird Cage & Regency Gallery
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10:45
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Plenary IB: Experimental Highlights (Chair: J. Stachel) Regency 2/3
Regency 2/3
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12:50
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14:15
Lunch 1h 25m Blue Room
Blue Room
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14:15
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16:20
Plenary IC: Initial State, Global & Collective Dynamics (Chair: L. McLerran) Regency 2/3
Regency 2/3
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15:05
PHENIX Results on Cold Nuclear Matter 25mSpeaker: Matthew Wysocki (University of Colorado at Boulder)
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Refreshment Break 30m Bird Cage & Regency Gallery
Bird Cage & Regency Gallery
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16:50
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18:30
Plenary ID: Initial State, Global & Collective Dynamics (Chair: B. Jacak) Regency 2/3
Regency 2/3
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17:15
Overview of results on flow and correlations from the CMS collaboration 25mThis talk will present an overview of collective flow phenomena and dihadron correlations from the CMS experiment at the LHC in pp and PbPb collisions. Fourier components of the anisotropic azimuthal distribution, ranging from the second to the sixth component, are obtained using different analysis techniques, which have different sensitivities to non-flow and flow fluctuation effects. Utilizing a novel and unique high-pT single-track high-level trigger, the results are presented over a broad pT range up to approximately 60 GeV/c, as a function of pseudorapidity and collision centrality. These new data will provide essential information on both the hydrodynamic properties of the medium at low pT and path length dependence of in-medium parton energy loss at high pT. Dihadron correlations are measured over a wide acceptance and pT range. Long-range near-side ("ridge") correlation structures are observed from low pT (1 GeV/c) to very high pT (at least 20 GeV/c). Their connection to the single-particle azimuthal anisotropy is extensively investigated via the factorization studies of Fourier decomposition of dihadron correlations. Short-range jet-like correlations are also systematically studied as a function of pT, pseudorapidity, centrality and compared to the results in pp collisions.Speaker: Stephen James Sanders (University of Kansas (US))
- 17:40
- 18:05
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19:30
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22:00
Reception - Luce Center of the Smithsonian American Art Museum 2h 30m Smithsonian Museum
Smithsonian Museum
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07:30
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08:30
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08:30
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10:45
Plenary IIA: Jets (Chair M. Gyulassy) Regency 2/3
Regency 2/3
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- 08:50
- 09:10
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10:30
Jet Discussion 15m
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10:45
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11:15
Coffee Break 30m Bird Cage & Regency Gallery
Bird Cage & Regency Gallery
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11:15
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12:50
Plenary IIB: Heavy Flavor (Chair: P. Giubellino) Regency 2/3
Regency 2/3
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11:15
Heavy Flavor Results from STAR 20mSpeaker: Wei Xie (Purdue University (US))
- 11:35
- 11:55
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12:35
Heavy Flavor Discussion 15m
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11:15
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12:50
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13:05
Conference Photo 15m
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13:05
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14:15
Lunch 1h 10m Blue Room
Blue Room
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14:15
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16:15
Parallel 1A: Global & Collective Dynamics (Chair U. Heinz) Regency 2/3
Regency 2/3
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14:15
Shocks in Quark-Gluon Plasma 20mLarge energy deposition from LHC quenching jets restarted interest to shock formation. Shocks also have theoretical significance as the simplest out-of-equilibrium setting without time dependence. While weak shocks have small gradients and can be treated hydrodynamically in the Navier-Stokes (NS) approximation, the ones without a small parameter (strong shocks) needs other methods. Two of those will be applied: (i) the ``resummed hydrodynamics" proposed earlier by Lublinsky and myself; and (ii) AdS/CFT correspondence, which uses the modified Einstein equations. In the latter case we apply novel variational approach and find approximate solution good to within fraction of a percent. The conclusion from both treatments is that the strong shocks deviate from NS only be few percent, in the direction of thinner shocks. We also discuss how shock formation shoulc modify the predictions for jet-hadron and hard hadron-hadron correlators.Speaker: Edward Shuryak (stony brook university)
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14:35
PHENIX Measurements of Higher-order Flow Harmonics for Identified Charged Hadrons in Au+Au Collisions at 39 – 200 GeV 20mCollective flow measurements continue to play an important role in ongoing efforts to map out the temperature dependence of the transport coefficient $\frac{\eta}{s}(T)$, for the strongly interacting matter produced in heavy ion collisions at RHIC. Recently, PHENIX has performed a detailed set of measurements of the higher-order flow coefficients ($v_{n}$ for n=2,3,4), for both inclusive and identified charged hadrons. The results from these new measurements in Au+Au collisions will be presented, as a function of $p_T$, centrality and beam collision energy, in concert with several scaling properties observed for these data. The role of these results as additional constraints for $\frac{\eta}{s}(T)$ will also be discussed.Speaker: YI GU (D)
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14:55
Beam Energy Dependence of First and Higher-Order Flow Harmonics from the STAR Experiment at RHIC 20mA primary goal of the RHIC Beam Energy Scan (BES) is to search for evidence of a transition between a hadron gas and a Quark Gluon Plasma. The dependence of $v_{1}$ and higher flow harmonics on system size and beam energy may be sensitive to the degrees of freedom in the system, as a consequence of early pressure gradients and a potential softening in the equation of state. In this talk, we present STAR measurements of $v_{1}$ for $\pi^\pm$, $K^\pm$, protons and antiprotons along with $v_{n}$ for charged particles from 7.7 GeV to 200 GeV. A striking observation is that the $v_1$ slope $F = dv_1 /dy$ for net protons, which is an estimate of the directed flow contribution from baryon number transported to the midrapidity region, changes sign twice within the BES energy range. In contrast, $F$ for all other particle types is negative at all studied energies. For charged particles, we observe a local minimum in integrated ($0.2 < p_T < 2.0$ GeV/$c$ and $|\eta| < 1.0)$ directed flow between 11.5 and 27 GeV for central 0-20\% collisions. At a similar centrality, we observe a shallow minimum in the energy dependence of $v_{3}$ for charged hadrons. We also show the ratio of the two-particle cumulant $v_{n}\{2\}$ to participant eccentricity($\varepsilon_{n, {\rm part}}$) to quantify how well the system converts initial geometry fluctuations into momentum-space correlations for different collision energies, system sizes and harmonics.Speaker: Yadav Pandit (Kent State University)
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15:15
Collision Energy Dependence of Viscous Hydrodynamic Flow in Relativistic Heavy-Ion Collisions 20mWe present a systematic study on the evolution of hadron spectra and their azimuthal anisotropy from the lowest collision energy studied at the Relativistic Heavy Ion Collider (RHIC), √s = 7.7A GeV, to the highest energy reachable at the Large Hadron Collider (LHC), √s = 5500A GeV [1]. As the collision energy increases, the resulting increases of the initial temperature, and fireball lifetime, as well as the evolution of the centrality dependence of final charged particle multiplicity are quantitatively studied and compared between the two most popular initial state models, the Monte Carlo Glauber and Monte-Carlo Kharzeev-Levin-Nardi (MC-KLN) models. For Glauber model initial conditions with a small specific shear viscosity eta/s = 0.08, the differential charged hadron elliptic flow v_2^{ch}(pT, √s) is found to exhibit a very broad maximum as a function of √s around top RHIC energy, rendering it almost independent of collision energy for 39 < √s < 2760A GeV. Compared to ideal fluid dynamical simulations [2], this "saturation" of elliptic flow is shifted to higher collision energies by shear viscous effects. For color-glass motivated MC-KLN initial conditions, which require a larger shear viscosity eta/s = 0.2 to reproduce the measured elliptic flow, a similar "saturation" is not observed up to LHC energies, except for very low pT. We emphasize that this "saturation" of the elliptic flow is not associated with the QCD phase transition, but arises from the interplay between radial and elliptic flow which shifts with √s depending on the fluid's viscosity and leads to a subtle cancellation between increasing contributions from light and decreasing contributions from heavy particles to v_2 in the √s range where v_2^{ch}(pT, √s) at fixed pT is maximal. By generalizing the definition of spatial eccentricity ecc_x to isothermal hyper-surfaces, we calculate ecc_x on the kinetic freeze-out surface at different collision energies. Up to top RHIC energy, √s=200A GeV, the fireball is still out-of-plane deformed at freeze out, while at LHC energy the final spatial eccentricity is predicted to approach zero. [1] Chun Shen and Ulrich Heinz, "Collision Energy Dependence of Viscous Hydrodynamic Flow in Relativistic Heavy-Ion Collisions,'', arXiv:1202.6620 [nucl-th]. [2] Gregory Kestin and Ulrich Heinz, "Hydrodynamic radial and elliptic flow in heavy-ion collisions from AGS to LHC energies,'' Eur. Phys. J. C 61, 545 (2009)Speaker: Chun Shen (Ohio State University)
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15:35
Non-linear anisotropic flow with ideal and viscous hydrodynamics 20mThe particle spectrum from RHIC and LHC can be decomposed into harmonic series that defines the dipolar flow $v_1$, the elliptic flow $v_2$, the triangular flow $v_3$, and $v_4$, and $v_5$ etc. To understand the origin of higher order harmonics, we extend the linear response formalism for anisotropic flow to include the non-linear response which results from the interactions between the lowest harmonics and the elliptic flow. For example, $v_{5(23)}/(\epsilon_2 \epsilon_3)$ records the $v_5$ generated by the non-linear interactions between $v_2$ and $v_3$. Ideal and viscous hydrodynamic calculations show that the non-linear response becomes dominant for n=4 and n=5 in non-central collisions. This trend is much more pronounced for viscous hydrodynamics where the linear response for n=4 and n=5 is negligible.Speaker: Mr Li Yan (Stony Brook University)
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15:55
Derivation of transient relativistic fluid dynamics from the Boltzmann equation for a multi-component system 20mWe present a general derivation of relativistic fluid dynamics from the relativistic Boltzmann equation using the method of moments [1]. The main difference between our approach and the traditional 14-moment approximation is that we do not close the fluid-dynamical equations of motion by truncating the expansion of the single-particle momentum distribution function. Instead, we keep all the terms in the moment expansion and truncate the exact equations of motion for these moments according to a systematic power counting scheme in Knudsen and inverse Reynolds numbers. We apply this formalism to obtain an approximate expression for the non-equilibrium single-particle momentum distribution function of a hadron resonance gas. Then, we investigate the implications of our new formalism in the freeze-out description of the hadron resonance gas and compare it with the method traditionally used in heavy-ion collisions, the 14-moment approximation. [1] G.S. Denicol, H. Niemi, E. Molnar, and D.H. Rischke, arXiv:1202.4551 [nucl-th].Speaker: Gabriel Denicol (Frankfurt University)
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Parallel 1B, Jets (Chair X.N. Wang) Palladian
Palladian
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14:15
Study of jet quenching using photon-jet events in PbPb collisions at 2.76 TeV with CMS 20mThe first measurement of the transverse momentum (pT) imbalance of isolated-photon+jet pairs in relativistic heavy ion collisions is reported. The analysis uses data from PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair and corresponding to an integrated luminosity of 150/ub recorded by the CMS experiment at the LHC in 2011. For events containing an isolated photon with transverse momentum pT > 60 GeV/c and an associated jet with pT > 30 GeV/c, the photon–jet pT imbalance is studied as a function of collision centrality and compared to pp data and PYTHIA calculations at the same center-of-mass energy. Using the pT of the isolated photon as an estimate of the energy of the associated parton at production, this measurement allows an unbiased characterization of the in-medium parton energy loss.Speaker: Yue Shi Lai (Massachusetts Inst. of Technology (US))
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14:35
Study of correlations between neutral bosons and jets in lead-lead collisions at 2.76 TeV with the ATLAS detector 20mThe correlations of jets with neutral bosons is a particularly powerful tool to probe the underlying physics of jet quenching. To gain insight into the physics of this process we can study Z-jet and gamma-jet correlations. Because the Z and photons do not directly couple to the strong force, in a jet+boson event the unmodified bosons allow us to access the modification of the opposite side jet; unlike dijet events, where both jets potentially lose energy, these bosons provide an excellent calibration of the energy of the recoil jet. The jets are measured in the same calorimeter, over a range of jet radii, and benefit from the detailed information about the shower profile. The ATLAS experiment has measured jet correlations with both direct photons as well as with Z bosons via dilepton channels in Pb+Pb collisions with sqrt(s_NN)=2.76 TeV in a data sample of nearly 150 ub^-1 of integrated luminosity. The measurement of these correlations will be presented.Speaker: Zvi Citron (Weizmann Institute of Science (IL))
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14:55
Prompt Photon Production and Photon-Jet Hadron Correlations in PHENIX at RHIC 20mA variety of heavy-ion data from RHIC and recently also from the LHC on hard direct photon production testifies that this "white" probe of the densely colored QGP continues to lend new insights to understanding jet suppression and energy loss. It also allows first comparisons between RHIC and LHC energies for the behavior of energy loss, for example whether jet fragmentation function is indeed modified by the energy loss process at any jet energy. Additionally, direct photon measurements in A+A since they are not affected by the final state QGP, offer an excellent way to test for non-trivial initial state effects, complementing recent PHENIX d+Au collision jet and single electron spectra data. To this end, we will report in this talk on new results of high pT single direct photon production in both p+p and Heavy Ion systems. For the hot final state QGP studies, PHENIX results on direct photon-jet "photon-hadron" correlations for QGP studies will also be presented. This will include a report on analyses of new datasets, which should be able to directly address the question of fragmentation function modification, along with the status of new analysis directions in PHENIX for this channel, such as event by event photon identification techniques in high multiplicity.Speaker: Justin Edward Frantz (Ohio University (US))
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15:15
Correlation between isolated photons and charged hadrons in pp and Pb-Pb collisions measured with ALICE 20mGamma-hadron correlations measured in heavy-ion collisions produced at the LHC allow to investigate medium induced jet modifications in a transverse momentum (p_t) range below 50 GeV/c, where jet reconstruction is challenging because of the relatively large contribution from the underlying event. At high p_t direct photons, produced in Compton and annihilation QCD leading order processes, are associated to a jet in opposite direction. Such processes are tagged experimentally by identifying leading isolated photons and their correlated associated hadrons in opposite azimuthal direction. The jet fragmentation is estimated from the hadrons and the photon p_t via the imbalance parameter x_E = -\vec{p_t,h}\vec{p_t,g} / |p_t,g|^2. The remaining contamination from neutral meson decay photons is subtracted statistically.We present the first results extracted from gamma-hadron correlations measured in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV, triggered by the ALICE electromagnetic calorimeters. Medium effects will be studied by comparison to results from pp collisions data at sqrt(s) = 7 TeV, combined with a smaller dataset at sqrt(s) = 2.76 TeV.Speaker: Nicolas Arbor (Centre National de la Recherche Scientifique (FR))
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15:35
Electroweak boson-tagged jet event asymmetries at the Large Hadron Collider 20mTagged jet measurements provide a promising experimental channel to quantify the similarities and differences in the mechanisms of jet production in proton-proton and nucleus-nucleus collisions. We present the first calculation of the transverse momentum asymmetry of $Z^0/\gamma^*$-tagged jet events in $\sqrt{s}=2.76$~TeV reactions at the LHC. Our results combine the ${\cal O}(G_F\alpha_s^2)$ perturbative cross sections with the radiative and collisional processes that modify parton showers in the presence of dense QCD matter. We find that a strong asymmetry is generated in central lead-lead reactions that has little sensitivity to the fluctuations of the underlying soft hadronic background. We present theoretical model predictions for its shape and magnitude. We also demonstrate the connection of our results to photon-tagged jet events and inclusive electroweak boson production.Speaker: Dr Ivan Vitev (LANL)
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Parallel 1C: Correlations & Fluctuations (Chair J. Schukraft) Diplomat
Diplomat
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Detailed HBT measurement with respect to event plane and collision energy in Au+Au collisions at PHENIX 20mThe HBT measurement provides the information on the space-time evolution of particle emitting source in relativistic heavy ion collisions. Azimuthal component of 3D HBT radii relative to event plane gives us the information of the source shape at freeze-out. It also provides the information of the system evolution by comparing with the initial source shape. The recent measurement of higher harmonic flow ($v_{3}$, $v_{4}$, etc) are measured at RHIC and LHC, which are primarily coming from the spatial fluctuation of the initial density on the collision area. Hydrodynamic model calculation reports that the shape by the initial fluctuation resulting in triangular component may be preserved until freeze-out. The HBT measurement relative to higher order event plane may show the feature if this is the case. We will present the recent results of azimuthal HBT measurement relative to 2^{nd} and 3^{rd} order event plane in Au+Au 200 GeV collisions at PHENIX. Eccentricity at freeze-out for charged pions and kaons will be compared and discussed. Also, triangularity at freeze-out for charged pions will be reported. The recent HBT measurement at lower energies will also be shown, and compared with 200GeV results.Speaker: Takafumi for the PHENIX Collaboration Niida (University of Tsukuba)
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14:35
Femtoscopy of identified particles at STAR. 20mMeasurement of correlations of pair of particles with small relative momenta provides insight into geometry and lifetime of particle emitting source in relativistic heavy ion collisions. Kaon femtoscopy extends the range of pair transverse mass covered and provides a sample less affected by decay resonances as compared to pions. The correlation functions of non-identical particles in the three-dimensional $\vec{k}^*$ space can reveal a space-time offset of one particle species (e.g. kaons) with respect to another (e.g. pions). Measurement of $\Lambda-\Lambda$ correlation is closely related to $H_{0}$-dibaryon, a six quark state predicted by Jaffe[1], which could appear as a bump in the $\Lambda-\Lambda$ invariant mass spectra or depletion in pair correlation near the threshold depending on the nature of $H_{0}$-dibaryon state. We present new measurements of pion-kaon, kaon-kaon and hyperon-hyperon correlations measured in Au+Au collisions at the STAR experiment during Run 10 and Run 11. The analysis greatly benefits from the STAR Time of Flight detector to extend particle identification capabilities. Kaon source sizes are extracted by using spherical harmonics decomposition technique. Dependence of the kaon source radii on event centrality and pair transverse momentum for $\sqrt{s_{NN}}$ = 7.7-200 GeV are presented. Centrality dependence of pion-kaon femtoscopy in at Au+Au $\sqrt{s_{NN}}$ = 200 GeV and a similar analysis for p+p collsions at $\sqrt{s_{NN}}$ = 200 GeV will be presented for the first time. Finally, we will present the measurement of $\Lambda-\Lambda$ correlations for $\sqrt{s_{NN}}$ = 39-200 GeV. [1] R. L. Jaffe,Phys. Rev. Lett. 38(1977) 195.Speakers: Neha Shah (UCLA), neha shah (University of California Los Angeles)
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Meson and baryon femtoscopy in heavy-ion collisions at ALICE 20mIn heavy-ion collisions produced at the LHC two-particle correlations of mesons and baryons carry important information about the emitting source. At low relative momentum femtoscopic correlations arise, which are sensitive to the homogeneity lengths of the system. Hydrodynamic models predict that these will decrease with increasing transverse mass of the pair. Such decrease is universally reported for pions, also at the LHC. Kaons and baryons, having a much larger mass, allow to significantly extend the range of measured m_T. The femtoscopic results for heavier particles would put a strong constraint on such predictions. Non-identical baryon and meson pairs are also sensitive to emission asymmetries. Femtoscopic correlations between baryons arise mostly due to the strong interaction, which is not precisely known for some baryon pair types. Most notable example is the lambda-lambda interaction which has an unknown contribution due to the potential existence of the H0 dibaryon. Equally interesting are baryon-antibaryon potentials, which have a significant contribution from annihilation channels. These processes may have an impact on single-particle spectra, and should be investigated as one of the possible sources of the small proton yield at the LHC. We show the two-particle correlation functions for several pair types (baryon-baryon, baryon-antibaryon and meson-meson), consisting of neutral and charged kaons, protons and lambdas. Femtoscopic analysis is carried out for them, taking into account, when necessary, residual correlations and annihilation channels. Results are presented as a function of transverse mass and event multiplicity, comparing with the pp collisions results when possible. Correlations with lambdas are analyzed both with femtoscopic methods as well as to study the unknown interaction potentials.Speaker: Maciej Pawel Szymanski (Warsaw University of Technology (PL))
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15:15
Short- and long-range very-high-pT triggered dihadron correlations in PbPb collisions at 2.76 TeV with CMS 20mNew precision measurements of dihadron correlations triggered by a very high-pT particle in 2.76 TeV PbPb collisions over a broad range of pseudorapidity and the full range of azimuthal angle will be presented. Utilizing a novel and unique high-pT single-track high-level trigger, the analysis explores the full 2011 PbPb data set corresponding to an integrated luminosity of 150/ub collected by CMS. For the first time, a long-range correlation structure up to |delta-eta|~4 at small delta-phi (near side) is observed for such very high-pT (e.g., pT~20 GeV/c) trigger particles correlated with low-pT (a few GeV/c) associated particles. The observed long-range correlations in |delta-eta| on the near side are consistent with the single-particle azimuthal anisotropy (characterized by the Fourier harmonics, vn) of high-pT trigger particles measured relative to the event-plane angle determined with the forward hadronic calorimeters. After subtracting the vn harmonics component, the shape and yield on the near (|delta-phi| < 1) and away (|delta-phi| > 1) side of the residual dihadron correlations have been studied systematically over a wide kinematic range in trigger (12 < pT[trig] < 50 GeV/c) and associated ( 0.5 GeV/c < pT[assoc] < pT[trig]) particle pT, as a function of pseudorapidity and collision centrality. The results are compared to those in pp collisions at the same energy.Speaker: Rylan Towne Conway (University of California Davis (US))
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15:35
Event shape engineering with ALICE 20mStrong fluctuations of the anisotropic flow and the large acceptance of the ALICE detector allow an efficient selection of the events corresponding to a specific initial geometry. This opens many new possibilities to study the properties of the system created in ultra-relativistic nuclear collisions. In this talk, using the Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$~TeV data, we demonstrate the ability of the method to select events with anisotropic flow values significantly larger or smaller than the average. For those events we present results on centrality and momentum dependence of the anisotropic flow obtained with different methods including two- and many-particle correlations. We also investigate obtaining the full $v_2$ distribution via unfolding methods.Speaker: Alexandru Florin Dobrin (Wayne State University (US))
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15:55
Azimuthal anisotropy of charged hadrons at very high pT in PbPb collisions at 2.76 TeV with CMS 20mMeasurements of the azimuthal anisotropy of charged hadrons are presented for PbPb collisions at 2.76 TeV over an extended transverse momentum range up to approximately 60 GeV/c. The data were collected with the CMS detector at the LHC. Utilizing a novel and unique high-pT single-track high-level trigger, the analysis explores the full 2011 PbPb data set corresponding to an integrated luminosity of 150/ub. Anisotropy parameters (v2, v3 and v4) are extracted by correlating charged tracks with the event plane angle reconstructed using the energy deposited in the forward calorimeters. By utilizing the broad coverage of the CMS foward calorimetry, contamination from back-to-back dijets is suppressed. The results presented in this talk significantly improve on the statistical precision of previous v2 measurements for pT> 12 GeV/c, and explore for the first time the harmonic components of the azimuthal dependence in the very high pT region beyond 20 GeV/c. Beyond pT>10 GeV/c, the observed v2 values show a moderate decrease with pT, being consistent with zero only above pT~40 GeV/c and for mid-central (30-60%) collisions. A common trend in the centrality dependence of v2 is observed for particles over a wide range of pT up to approximately 48 GeV/c that is independent of pseudorapditiy, suggesting a potential connection to the initial geometry. These new data can impose quantitative constraints on the details of in-medium parton energy loss models, particularly the influence of the path length and the shape of the interaction region.Speaker: Victoria Zhukova (University of Kansas (US))
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Parallel 1D: Heavy Flavor & Quarkonia (Chair R. Granier de Cassagnac) Empire
Empire
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14:15
Detailed measurements of charmonium suppression in PbPb collisions at 2.76 TeV with CMS 20mCMS has measured the nuclear modification factors of prompt J/psi in PbPb collisions at sqrt(sNN) = 2.76 TeV. For prompt J/psi with relatively high pT (6.5 < pT < 30 GeV/c), a strong, centrality-dependent suppression is observed in PbPb collisions, compared to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions. During the 2011 data taking period the data sample has been increased by a factor of twenty, which allows for more detailed charmonium measurements, e.g. mapping the transverse momentum and centrality dependence of the nuclear modification simultaneously. New results on charmonium suppression based on the full available 2011 data sample will be reported.Speaker: Dong Ho Moon (Korea University (KR))
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14:35
Jpsi and psi (2S) production in Pb-Pb collisions with the ALICE Muon spectrometer at the LHC 20mALICE is the LHC experiment dedicated to the study of heavy ion collisions. The main purpose of ALICE is to investigate the properties of a new state of deconfined nuclear matter, the Quark Gluon Plasma. Quarkonium measurements will play a crucial role in this investigation. In particular, the sequential suppression of the quarkonium states by color screening has long being suggested as a signature and thermometer of the QGP.Speaker: Roberta Arnaldi (Universita e INFN (IT))
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14:55
Heavy quark potential at non-zero temperature and quarkonium spectral functions 20mWe calculate different types of Wilson loops of temporal size t < 1/T at non-zero temperatures on the lattice using Highly Improved Staggered Quark (HISQ) action and temporal extent Nt=8 and 12. Unlike other static correlators which go around the periodic boundary these Wilson loops are not related to the free energy of static quark anti-quark pair. Therefore from the analysis of the Wilson loop we extract the real part of the heavy quark potential. We find that the extracted potential is systematically larger than the singlet free energy calculated on the lattice. At T>200MeV we supplement the calculated real part of the potential with the imaginary part obtained in perturbation theory and evaluate the quarkonium spectral functions. We find that all quarkonium states except the Upsilon(1S) melt at temperatures T>300MeV. Finally from the obtained spectral functions we calculate the Euclidean correlation functions and compare them with available lattice data.Speaker: Peter Petreczky (BNL)
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Recent Heavy Quarkonia Results from PHENIX 20mThe idea of using heavy quarkonia production as a direct probe of the screening length in the quark gluon plasma (QGP) has been around for over two decades. Suppression of quarkonia production in heavy ion collisions has been measured at the SPS, RHIC, and the LHC, including new measurements of $\Upsilon(1S+2S+3S)$ production in Au+Au collisions by PHENIX. However, a full understanding of these results in terms of direct contributions from the QGP is still evolving. An incomplete knowledge of the baseline cold nuclear matter (CNM) effects, as well as the possibility of competing effects present in the QGP, such as recombination, has hindered a full understanding of the observed heavy ion results. In order to quantify the CNM effects present at RHIC, PHENIX has measured both $J/\psi$ and $\Upsilon$ production in $d$+Au collisions over a wide range in rapidity with the inclusion of new measurements of $\Upsilon(1S+2S+3S)$ production at midrapidity. PHENIX finds a suppression relative to $p$+$p$ collisions which is greater at forward rapidity and similar between the $J/\psi$ and $\Upsilon$, leading to interesting implications of the RHIC heavy ion results. New measurements of the transverse momentum dependence of the $J/\psi$ nuclear modification factor provide further constraints on CNM effects, as well as constraining the Cronin effect at RHIC energies. This talk will present recent heavy quarkonia results in $p$+$p$, $d$+Au and Au+Au collisions from PHENIX, as well as the implications of the measured CNM effects on the heavy ion data.Speaker: Darren McGlinchey (F)
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Quarkonia production in the STAR experiment 20mThe suppression of quarkonia production in high energy nuclear collisions relative to proton-proton collisions, due to the Debye screening of the quark-antiquark potential, was proposed as a signature of the formation of Quark-Gluon Plasma. However, there are other effects that may affect the observed quarkonia production, such as cold nuclear matter effects, final state nuclear absorption and statistical coalescence of quark-antiquark pairs. Studies of production of various quarkonia states in heavy-ion collisions can provide insight into the properties of the hot and dense medium created in relativistic heavy-ion collisions at RHIC. Systematic measurement of the quarkonia production for different colliding systems, centralities and collision energies may help to understand the quarkonia production mechanisms as well as the medium properties. Furthermore, at RHIC energies the $\Upsilon$ meson is a clean probe of the early system due to negligible contributions from $b$-$\bar{b}$ recombination and non-thermal suppression from co-mover absorption. In this talk we will present results on J/$\psi$ and $\Upsilon$ production via the dielectron decay channel in Au+Au, $d$+Au and $p+p$ collisions at midrapidity at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment. We will show the J/$\psi$ nuclear modification factor as a function of centrality and $p_{T}$ and the $\Upsilon$ nuclear modification factor computed using the new preliminary $p$+$p$ result from 2009, in Au+Au and $d$+Au collisions. We will also present the J/$\psi$ polarization measurement in $p$+$p$ collisions and the J/$\psi$ elliptic flow measurement in Au+Au collisions. Furthermore analysis status of J/$\psi$ production in Au+Au collisions at 39 GeV and 62.4 GeV will be reported.Speaker: Barbara Trzeciak (Warsaw University of Technology)
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Comprehensive Analysis of in-Medium Quarkonia from SPS to LHC 20mWe employ a kinetic rate-equation approach in a thermally expanding medium to compute the suppression and regeneration of quarkonia in heavy-ion collisions [1]. The in-medium properties of quarkonia figuring into the rate equation (widths, binding energies and heavy-quark masses) are constrained by euclidean correlators from lattice QCD. Input cross sections for heavy quarks and quarkonia, as well as cold nuclear matter effects, are constrained by pp and pA/dA data as available. Formation-time effects and bottom feeddown, mostly relevant at high transverse momentum (p_t), are accounted for. The thermal relaxation time of heavy quarks, controlling the regeneration contribution, is adjusted to central AA data at SPS and RHIC. The approach is applied to pre- and postdict charmonium [1,2] and bottomonium [3] production as a function of centrality, p_t, rapidity, and collision energy in comparison to data from NA50, PHENIX, STAR, ALICE, CMS and ATLAS. Systematic trends and areas of potential disagreement are identified. [1] X. Zhao and R. Rapp, Phys. Rev. C82 (2010) 064905. [2] X. Zhao and R. Rapp, Nucl. Phys. A859 (2011) 114. [3] A. Emerick, X. Zhao and R. Rapp, Eur. Phys. J. A (2012) in press.Speaker: Ralf Rapp (Texas A&M University)
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Coffee Break 30m Bird Cage & Regency Gallery
Bird Cage & Regency Gallery
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Parallel 2A: Global & Collective Dynamics (Chair A. Poskanzer) Regency 2/3
Regency 2/3
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16:45
Measurement of elliptic and higher-order harmonics at 2.76 TeV Pb-Pb collisions with the ATLAS detector 20mAnisotropy coefficients v_n are important observables for studying the hot, dense medium created in heavy ion collisions. They not only probe the collective flow of the bulk medium (at pT<3-4 GeV), but also probe the path-length dependent energy loss (at higher pT), both are associated with the asymmetries in the initial geometry. However, auto-correlations not related to initial geometry, commonly referred to as non-flow effects, can contribute to these coefficients, hence need to be systematically suppressed. We present comprehensive measurements of coefficients v_2-v_6 using the event plane method and two-particle correlations method in broad p_T, eta and centrality ranges using the Pb-Pb data from the ATLAS experiment. The phase space regions where the two methods are consistent and where they disagree are explored, and the role of harmonic flow, path-length dependence of jet quenching, and non-flow effects in different part of the phase space are clarified. These detailed measurements provide new insights into the hydrodynamic picture at low pT, the jet energy loss picture at high pT, and the nature of the fluctuations in the initial geometry; they also provide a natural explanation for the "ridge" structures observed in two-particle correlation functions.Speaker: Dominik Karol Derendarz (Polish Academy of Sciences (PL))
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17:05
Shear viscosity of the quark-gluon plasma from flow in heavy-ion collisions 20mWe report an extraction of the ratio of shear viscosity to entropy density (eta/s) of the medium created in relativistic heavy-ion collisions at the LHC. With a significant improvement of one of the main sources of theoretical uncertainty, we are able for the first time to quote a precise average value with robust error bars, systematically accounting for all known sources of systematic error (theoretical and experimental).Speaker: Matthew Luzum (IPhT Saclay)
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17:25
Pseudorapidity density of charged particles in a wide pseudorapidity range and its centrality dependence in Pb-Pb collisions at 2.76 TeV 20mIn this talk we present a measurement of the pseudorapidity distribution in the range −5 < eta < 5.25, for different centralities in Pb-Pb collisions at sqrt(s_NN) =2.76 TeV. This also allows us to estimate the total number of produced charged particles. The measurement is performed exploiting LHC satellite bunches, that is bunches captured in non-nominal RF buckets. These give rise to displaced vertices in the range −187.5 < zvtx < 375 cm, allowing the ALICE forward detectors (VZERO and FMD) to cover a wide pseudorapidity window. The dependence of dNch/deta on the number of participant nucleons or on the number of binary collisions is sensitive to mechanisms underlying particle production (eg. the effect of gluon saturation). In this contribution ALICE data will be compared to current models and an analysis of the longitudinal scaling will be performed.Speaker: Maxime Rene Joseph Guilbaud (Universite Claude Bernard-Lyon I (FR))
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17:45
Pseudorapidity and centrality dependence of transverse energy flow in PbPb collisions at 2.76 TeV from CMS 20mThe transverse energy flow in PbPb collisions at 2.76 TeV nucleon-nucleon center-of-mass energy has been measured over a broad range of centrality for pseudorapidities between -5.2 and 5.2 using the CMS detector at the LHC. This analysis is based on 0.306/ub of data from 2010, with recently extended number (and range) of pseudorapidity and centrality bins. The transverse energy per unit of pseudorapidity increases faster with collision energy than the multiplicity of charged particles. This implies that the mean energy per particle and hence the temperature of the system is increasing with collision energy. The amount of transverse energy produced per participating nucleon increases with centrality and with collision energy. The centrality dependence of transverse energy production has only a weak dependence on pseudorapidity and collision energy. For the most central collisions, the energy density is estimated to be 11.3 +- 0.6 GeV/fm3 at a time of 1 fm/c after the collision, which is 2.8 times higher than the value reported at sqrt(sNN)=200 GeV.Speaker: Dr Magdalena Malek (University of Illinois at Chicago (US))
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18:05
E-by-E MUSIC Afterburner 20mHydrodynamic models enjoy much success in describing and predicting the bulk dynamics of relativistic heavy ion collisions. Recent studies have clearly shown that including initial and final fluctuations is essential for detailed study of the evolving QGP. So far, however, not many studies appeared which incorporate both fluctuations at the same time. Here we present our first results in including both the initial and final state fluctuations by combining the event-by-event 3-D viscous hydrodynamics model (MUSIC) with the publicly available UrQMD afterburner. Influence of these fluctuations on particle spectra, elliptic flow and higher harmonics will be presented.Speaker: Sangyong Jeon (McGill University)
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Parallel 2B: Jets (Chair P. Jacobs) Palladian
Palladian
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Studies of jet quenching and b-jet tagging in PbPb collisions at 2.76 TeV with CMS 20mThis presentation describes jet measurements in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV performed with the CMS detector at the LHC. With data from the 2011 Run, dijet measurements have been extended to large transverse momentum, up to 350 GeV/c. The dijet momentum balance and angular correlations are studied in detail as a function of collision centrality and leading jet transverse momentum. For the most peripheral PbPb collisions, the dijet momentum balance distributions are in good agreement with pp data and with reference calculations at the same collision energy. More central collisions show a strong imbalance between the leading and subleading jet transverse momenta, which is found to persist to the largest values of leading jet transverse momenta studied. The flavor dependence of jet quenching is a powerful handle to discriminate models of parton energy loss in heavy ion collisions. We demonstrate the capacity of CMS to identify jets initiated by bottom quarks using displaced vertices reconstructed in the silicon tracking system. The b-jet to inclusive jet ratio is measured in PbPb collisions and compared pp collisions at the same center-of-mass energy.Speaker: Matthew Nguyen (Ecole Polytechnique (FR))
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17:05
Measurements of jet suppression with ATLAS 20mThe energy loss of high-pt partons through the phenomenon of jet quenching provides insight into the transport properties of the medium created in relativistic heavy ion collisions. Evidence for this energy loss was first experimentally established through observation of high-pt hadron suppression at RHIC. This observable is not ideal for detailed quenching measurements as the final state hadrons are only relatable to the jet through the fragmentation. More recently, measurements of fully reconstructed jets have been performed at the LHC. This talk presents the latest experimental results from the ATLAS collaboration on jet suppression. These results establish qualitative features of the jet quenching mechanism as experimental fact and provide constraints on models of jet energy loss.Speaker: Aaron Richard Angerami (Columbia University (US))
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17:25
Inclusive jet and charged hadron nuclear modification factors in PbPb collisions at 2.76 TeV with CMS 20mMeasurements of charged hadron and inclusive jet transverse momentum (pT) spectra in pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV with the CMS detector will be reported. These measurements make use of the high-statistics jet-triggered data recorded in 2011, including the total available PbPb luminosity of 150/ub. Charged particles are reconstructed using an iterative algorithm and spurious high-pT tracks are suppressed by requiring appropriate energy deposits in the calorimeter system. Jets are reconstructed with the anti-kT algorithm, using combined information from tracking and calorimetry. The charged particle and jet transverse momentum distributions are measured in the pseudorapidity range of |eta|<1 and |eta| < 1.6, and in pT up to 100 GeV/c, and from 100 to 300 GeV/c, respectively. The nuclear modification factors, RAAs, for charged hadrons and jets are presented as a function of pT and collision centrality. In the range pT = 5-10 GeV/c the charged hadron production in PbPb collisions is suppressed by up to a factor of seven, compared to the pp yield scaled by the number of incoherent nucleon-nucleon collisions. The charged hadron RAA increases at higher pT and approaches a value of approximately 0.5 in the range pT = 40-100 GeV/c.Speaker: Marguerite Belt Tonjes (University of Maryland (US))
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17:45
Quantifying a Possibly Reduced Jet-Medium Coupling of the sQGP at the Large Hadron Collider 20mRecent LHC data on the nuclear modification factor of jet fragments suggest that the jet-medium coupling at the Large Hadron Collider (LHC) may be reduced relative to the coupling at the Relativistic Hadron Collider (RHIC). We estimate the magnitude of that reduction from a combined fit to the data on the nuclear modification factor and on the elliptic flow at both RHIC and LHC energies over a broad centrality range and a momentum range of 5-100 GeV. We also compare Glauber and Color Glass Condensate initial conditions using a simple analytic energy-loss model that can interpolate between weakly-coupled tomographic and strongly-coupled holographic jet-energy loss models. We find that an approximately 10% reduction of the jet-medium coupling from RHIC to LHC can account for the observed LHC data in reasonable accord with the magnitude expected from a running coupling associated with doubling the density of the strongy-coupled Quark-Gluon Plasma (sQGP) from RHIC to LHC.Speaker: Barbara Betz (Frankfurt University)
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18:05
Inclusive jet spectra in 2.76 TeV Pb-Pb collisions from the ALICE experiment 20mMeasurements of high-pt particle production in heavy-ion collisions at RHIC have shown that medium-induced energy loss affects the partons produced in the early stage of a heavy-ion collision. The increased initial production cross section for partons at LHC energies makes fully reconstruted jets available in a wide kinematic range, which allows for a differential investigation of parton energy loss. Partonic energy loss allows us to access important observables for the study of the hot deconfined nuclear matter produced in heavy ion collisions. The inclusive cross-section of reconstructed jets using the ALICE tracking detectors and electromagnetic calorimeter is presented from data collected during the 2.76 TeV Pb-Pb runs. The procedures used to reconstruct jets and extract them from a fluctuating background are discussed. The results will also be compared with jet yields from proton-proton collisions, which allows quantification of the medium-induced quenching effects.Speaker: Rosi Jan Reed (Yale University (US))
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Parallel 2C: Correlations & Fluctuations (Chair X. Dong) Diplomat
Diplomat
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16:45
Search for QCD Phase Transitions and the Critical Point Utilizing Particle Ratio Fluctuations and Transverse Momentum Correlations from the STAR Experiment. 20mDynamical fluctuations in globally conserved quantities such as baryon number, strangeness, charge, and isospin are suggested to carry information about the de-confinement and chiral phase transitions. An observation of enhanced dynamical fluctuations or non-monotonic behavior of transverse momentum correlations as a function of colliding energy might indicate the system has probed the predicted QCD critical point. The STAR experiment has performed a comprehensive study of the energy and charge dependence of dynamical particle ratio ($K/\pi$, $p/\pi$, and $K/p$) fluctuations, net-charge fluctuations, and transverse momentum correlations in the STAR TPC at mid-rapidity, as well as neutral-charge pion fluctuations at forward rapidity. The charge dependence of particle ratio fluctuations exhibit differences between same and opposite sign dynamical particle ratio fluctuations compared to inclusive charged dynamical fluctuations. Neutral-charge pion fluctuations at forward rapidity are measured by detecting neutral pion decay photons in the Photon Multiplicity Detector and charged pions by the Forward Time Projection Chamber, which cover the same pseudorapidty region. The centrality, energy, and charge dependence from new measurements of the fluctuation observables $\nu_{dyn}$ and $r_{m,1}$ and the energy dependence of transverse momentum correlations from $\sqrt{s_{NN}}$ = 7.7-200 GeV Au+Au collisions will be presented. These results are also compared to theoretical predictions from models such as HIJING and UrQMD.Speaker: Mr Prithwish Tribedy (for the STAR collaboration)
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17:05
Studies of net-charge fluctuations and balance functions with the ALICE detector at the LHC 20mThe creation of a strongly interacting deconfined Quark Gluon Plasma (QGP) phase in relativistic heavy-ion collisions can be studied by the fluctuations of conserved quantities like net-charge, and correlations between positive and negative pairs by using the method of Balance functions. Net-charge fluctuations are sensitive to the number of charges present in the system, thus the fluctuations in the QGP, with fractionally charged partons, are expected to be different from those of the hadron gas with unit charged particles. Lattice calculations suggest that the higher moments of net-charge distributions and their products are sensitive to the correlation length, and are related to the thermodynamic susceptibilities of the system. The method of the Balance function, on the other hand, is sensitive to collective flow and the breakup temperature and was proposed to give a handle on the hadronization time. A combined study of net-charge fluctuations with Balance functions provides insight to the properties of matter created in high energy collisions. We will present the first results of net-charge fluctuations, higher moments of net-charge distributions and Balance functions for Pb-Pb collisions at √sNN = 2.76 TeV measured by the ALICE experiment at the LHC. The results from net-charge fluctuations, presented in terms of νdyn and D-measure, are compared to predictions for a system initially dominated by a QGP, as well as for a hadron resonance gas. The widths of the Balance functions in pseudorapidity and azimuthal angle for non-identified charged particles show a clear centrality dependence, consistent with the picture of a delayed hadronization but also with a system exhibiting larger radial expansion in central collisions. A comparison of the results will be made to lower energy collisions at SPS and RHIC as well as to several models that incorporate collective effects.Speaker: Michael Weber (University of Houston (US))
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17:25
Study of the Sixth Order Cumulant of Net-proton Distributions Measured in STAR at RHIC 20mIn high-energy nuclear collisions, we study the properties of the excited nuclear matter with QCD degrees of freedom and search for the signals of the QCD phase transition. The ratios of the cumulants of conserved number distributions are sensitive to the correlation length of the system created in heavy-ion collisions, hence they are considered as good observables to study phase transitions. QCD based calculations suggests that the ratios of the sixth to second ($C_{6}/C_{2}$) order cumulants of the net baryon number distributions will change rapidly in the phase transition region of the QCD phase diagram. They are found to deviate considerably from predictions of the hadron resonance gas model which reproduce the fourth to second ($C_{4}/C_{2}$) order cumulants of the net proton number distributions at RHIC top energies. The STAR experiment, with large and uniform acceptance and excellence in particle identification, is ideal to study the QCD phase structure. The data collected in 2010 and 2011 allow us to study the $C_{6}/C_{2}$ ratio. In this talk, we will present the ratio of the sixth to second order cumulants of net-proton multiplicity distributions from minimum biased Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 27, 39, 62.4 and 200 GeV. Both protons and anti-protons are cleanly identified within $|y|<0.5$ and 0.4$< p_{T} <$0.8 GeV/c by the STAR Time Projection Chamber. For beam energies above 39 GeV, the ratios are consistently close to but below unity, while they have larger values below 39 GeV. Some implications of the new results will be discussed within the context of Polyakov loop-extended-Quark-Meson (thermal model) and UrQMD (transport model) models.Speaker: Ms Lizhu Chen (Central China Normal University)
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17:45
Mixed harmonic charge dependent azimuthal correlations in Pb-Pb collisions at 2.76TeV measured with the ALICE experiment at the LHC 20mThe charge dependence of the azimuthal correlations between produced hadrons is an important probe of the QGP matter created in relativistic heavy-ion collisions. In this talk, we will present the mixed harmonic charge dependent azimuthal correlations measured at mid-rapidity in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV by the ALICE Collaboration at the LHC. We observe a clear charge separation of hadrons with respect to the reaction plane measured via the mixed harmonic multi-particle technique. Implications from these measurements for the possible effects of local parity violation in the strong interaction and for models which incorporate the effects of local charge conservation on freeze-out surface and azimuthal flow will be discussed.Speaker: Yasuto Hori (University of Tokyo (JP))
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18:05
Charge balancing and the fall off of the ridge 20mThe puzzle of the fall-off of the same-side ridge in relative pseudorapidity, found in unbiased two-particle correlations, is solved. We show that the event-by-event hydrodynamics followed by statistical hadronization with proper charge conservation provides the crucial non-flow component and leads to agreement with the data at soft transverse momenta (p_T < 2 GeV). The fall-off of the same-side ridge follows from the fact that a pair of particles with opposite charges is emitted from the same fluid element, whose collective velocity collimates the momenta of the pair. Basic experimental features of the two-dimensional correlation functions are then represented, including the dependence on the relative charge (like-sign and unlike-sign pairs) and centrality. Related quantities, such as the charge balance functions or the dependence of the harmonic flow coefficients on relative pseudorapidity, are also properly explained in our approach.Speaker: Piotr Bozek
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Parallel 2D: Heavy Flavor & Quarkonia (Chair J.-P. Blaizot) Empire
Empire
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16:45
Detailed measurements of bottomonium suppression in PbPb collisions at 2.76 TeV with CMS 20mThe three Y states (1S, 2S, 3S) can be separated using the CMS experimental apparatus via their dimuon decays in both pp and heavy-ion collisions. A suppression of the Y(1S) and Y(2S) mesons is observed in PbPb collisions at sqrt(sNN) = 2.76 TeV, compared to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions. Furthermore, a suppression of the excited Y states has been measured with respect to the Y(1S) state, expressed as a double ratio [Y(2S+3S)/Y(1S)]{PbPb} / [Y(2S+3S)/Y(1S)]{pp}. The centrality dependence of the double ratio, as well as the nuclear modification factors (RAA) of the Y(1S) and Y(2S) states will be presented as a function of collision centrality, based on the analysis of the full data sample collected during the 2011 PbPb run, which corresponds to an integrated luminosity of 150/ub.Speaker: Guillermo Breto Rangel (University of California Davis (US))
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17:05
Momentum dependences of charmonium properties from lattice QCD 20mWe study the momentum dependence of charmonia in a hot medium using lattice QCD calculations. We analyze correlation functions and extract spectral functions from quenched calculations on large lattices close to the continuum limit in the temperature region $1.5<T/T_c<3$ as well as for $T\simeq 0.75T_c$. We examine the modifications of dissociation temperatures of the bound states when they are in motion with respect to the heatbath frame. We will also discuss the charm diffusion coefficients in connection with transport properties of charm quark at finite momentum. Furthermore, we expect to be able to present preliminary results at temperatures closer to the transition temperature, i.e. $T_c<T<1.5T_c$, which is crucial to locate the dissociation temperature of $J\psi$ and examine the sequential suppression scenario[1]. [1] H.-T. Ding, A. Francis, O. Kaczmarek, F. Karsch, H. Satz and W. Soeldner, BI-TP 2012/13, to appear on arXiv soonSpeaker: Heng-Tong Ding (Brookhaven National Lab)
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17:25
J/psi production at mid-rapidity in Pb-Pb collisions at 2.76 TeV 20mThe hot and dense nuclear matter created in nuclear collisions at relativistic energies consists of a plasma of deconfined quarks and gluons. Due to their large mass, the charm quarks are mainly formed in the first instants of the nuclear collision and will consequently experience the full history of the system. It was predicted that the strongly bound J/Ã state will be suppressed in the hot and deconfined quark-gluon plasma due to the color screening effect. This effect was already observed in Au-Au collisions at sqrt(s_NN) = 200 GeV at RHIC. It was also predicted that high production yields of charm quarks in nucleus-nucleus collisions at RHIC and especially at LHC energies will make possible (re)combination thus possibly leading to J/psi enhancement compared to lower energy nuclear collisions and to pp collisions. ALICE measures the J/psi at mid-rapidity, |y| < 0.9, down to zero transverse momentum. The reconstruction is performed using the J/psi decay into the di-electron channel. The electron identification is done using energy loss in gaseous detectors (the Time Projection Chamber and the Transition Radiation Detector) and the time-of-flight method (Time Of Flight detector). We will present the J/psi nuclear modification factor as a function of the collision centrality. Discussions and comparisons to theoretical calculations will be provided. First results and perspectives on the J/psi production with respect to the event plane (elliptic flow) will also be shown.Speaker: Ionut Cristian Arsene (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
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17:45
Gluon saturation effects on the color singlet J/Psi production in high energy dA and AA collisions 20mWe discuss the gluon saturation/color glass condensate effects on J/Psi production in high energy pA and AA collisions. We report the results of numerical calculations of the corresponding nuclear modification factors. We found a good agreement between our calculations and the experimental data on J/Psi production in pA collisions. We also observe that cold nuclear modification effects alone cannot describe the data on J/psi production in AA collisions. Our numerical calculations indicate that the discrepancy arises in a significant part from the higher pT’s. Additional final state suppression (at RHIC) and enhancement (at LHC) mechanisms are required to explain the experimental observations.Speaker: Kirill Tuchin (Iowa State University)
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18:05
High transverse momentum quarkonium production and dissociation in heavy ion collisions 20mWe calculate the yields of quarkonia in heavy ion collisions at RHIC and the LHC as a function of the transverse momentum. We focus on the consistent implementation of dynamically calculated nuclear matter effects, such as coherent power corrections, cold nuclear matter energy loss, and the Cronin effect in the initial state, and collisional dissociation of quarkonia in the final state as they traverse through the QGP. This formalism has been previously used to successfully describe the phenomenology of open heavy flavor (B and D mesons) both at RHIC and the LHC. We will briefly review the comparison with new open heavy flavor data and describe the extension of the calculation for quarkonium production. Based upon non-relativistic quantum chromodynamics, our calculations include both color-singlet and color-octet contributions and feed-down effects from excited states. Theoretical results are presented for $J/\psi$ and $\Upsilon$ and compared to experimental data where applicable. At RHIC, a good description of the high-$p_T$ $J/\psi$ modification observed in central Cu+Cu and Au+Au collisions can be achieved within the model uncertainties. We find that $J/\psi$ measurements in proton(or deuteron)-nucleus reactions are needed to constrain the magnitude of cold nuclear matter effects, and new data from d+Au collisions at RHIC already puts a strong limit on the Cronin enhancement for $J/\psi$. At the LHC, a good description of the experimental data can be achieved only in mid-central and peripheral Pb+Pb collisions. The large five-fold suppression of prompt $J/\psi$ in the most central nuclear reactions suggests the presence of thermal effects at the level of the quarkonium wavefunction, even at large transverse momentum.Speaker: Dr Rishi Sharma (TRIUMF)
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Parallel 3A: Global & Collective Dynamics (Chair T. Kodama) Regency 2/3
Regency 2/3
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08:30
Bulk viscosity, particle spectra and flow in heavy-ion collisions 20mWe study the effects of bulk viscosity on $p_T$ spectra and elliptic flow in heavy ion collisions. For this purpose we compute the dissipative correction $\delta f$ to the single particle distribution functions in leading-log QCD, and in kinetic models of a hadronic resonance gas. We find that for a near conformal fluid the bulk viscosity is suppressed by two powers of the conformal breaking parameter, but the viscous correction to the spectra is only suppressed by the first power. This implies that bulk viscous corrections to flow profiles are typically small, but corrections to the spectra can be significant. From an analysis of the spectra at RHIC and LHC we find that the bulk viscosity at freezeout cannot be large, $\zeta/s<0.05$. We also find, however, that a non-zero bulk viscosity improves the description of the hadrochemistry of flow, for example the splitting between the $v_2(p_T)$ of protons and pions.Speaker: Thomas Schaefer (N)
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08:50
Initial state fluctuations and higher harmonic flow in heavy-ion collisions 20mWe present recent developments in describing anisotropic flow in heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory and the Large Hadron Collider (LHC) at CERN with a relativistic 3+1 dimensional viscous event-by-event hydrodynamic simulation. We present results for elliptic, triangular and higher harmonic flow coefficients, including comparisons to first experimental data as well as predictions. We demonstrate the great potential of a systematic study of higher harmonic and directed flow to pin down the shear viscosity to entropy density ratio of the created quark gluon plasma and the details of the initial state.Speaker: Bjoern Schenke
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09:10
Higher harmonics flow measurement of charged hadrons and electrons in wide kinematic range with PHENIX VTX tracker 20mCollective flow is one of the key measurements to study the hot and dense matter created in heavy ion collisions, because it relates closely to early evolution of the matter. In particular, higher harmonic flow measurements plays an important role in constraining theoretical model calculations describing properties of the matter. The silicon vertex tracker (VTX) was installed into the PHENIX experiment in 2010 and it successfully collected approximately 5 billion events of Au+Au collisions at 200 GeV in 2011 RHIC run. The VTX is a four-layer silicon tracker and it can reconstruct charged particle tracks in a wide range of pseudo-rapidity (|eta|< 1.2) and almost 2 pi in phi. With this capability, it can measure elliptic flow v2 and higher harmonics flow (v3, v4, ...) of charged hadrons in a wide eta range. The main function of the VTX is separation of heavy flavor hadrons, charm and bottom. By identifying electrons with PHENIX central detectors, higher harmonic flow of electrons from heavy flavor decay can be determined over a broad pT range. In this talk, we will present measurement results on v2 and higher harmonic flow of charged hadrons and heavy flavor electrons, as well as comparison with theoretical models.Speaker: Dr maki kurosawa (RBRC)
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09:30
Two- and Multi-particle cumulant measurements of vn and isolation of flow and nonflow in 200 GeV Au+Au Collisions by STAR 20mAzimuthal anisotropic flows vn, arising from the anisotropic collision geometry, reflect the hydrodynamic properties of the quark gluon plasma created in relativistic heavy-ion collisions. A long standing issue in vn measurements is the contamination of nonflow, caused by intrinsic particle correlations unrelated to the collision geometry. Nonflow limits, in part, the precise extraction of the viscosity to entropy density ratio eta/s from data-model comparisons. Isolation of flow and nonflow is critical to the interpretation of the Fourier decomposition of dihadron correlations. In this talk we report measurements of vn azimuthal anisotropies using the two- and mult-particle Q-cumulants method from STAR in Au+Au collisions at 200 GeV. The centrality and pT dependence of vn will be presented. We compare the four- and six-particle cumulant measurements to gain insights on the nature of flow fluctuations [1,2]. We further analyze two- and four-particle cumulants between pseudo-rapidity (eta) bins. Exploiting the collision symmetry about mid-rapidity, we isolate the \Delta\eta-dependent and \Delta\eta-independent correlations in the data with a data-driven method [3]. The \Delta\eta-dependent part arises from near-side nonflow correlations, such as HBT interferometry, resonance decays, and jet-correlations. The \Delta\eta-independent part is dominated by flow and flow fluctuations with relatively small contribution from away-side jet-correlations. The method does not make assumptions about the eta dependence of flow. Our isolated \Delta\eta-independent part from data, dominated by flow, however, is found to be also eta-independent within the STAR TPC of +-1 unit of pseudo-rapidity. The \Delta\eta drop in the measured two-particle cumulant appears to entirely come from nonflow. We assess the effect of the nonflow on eta/s extraction. We reexamine the high-pT triggered dihadron correlations with background subtraction of our decomposed flows. [1] S.A. Voloshin, A.M. Poskanzer, A. Tang, and G. Wang, Phys. Lett. B659, 537 (2008). [2] L. Yi, F. Wang, and A. Tang, arXiv:1101.4646 [nucl-ex]. [3] L. Xu, L. Yi, D. Kikola, J. Konzer, F. Wang, and W. Xie, arXiv:1204.2815 [nucl-ex].Speaker: Li Yi (Purdue University)
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Study of higher harmonics based on (3+1)-dimensional relativistic viscous hydrodynamics 20mCurrently a possible origin of "Mach-Cone-like structure" is regarded as triangular flow and higher harmonics which are produced through event-by-event fluctuated initial states, which is a push to implement effects of event-by-event fluctuations in the initial conditions of relativistic hydrodynamic models. When the hydrodynamic simulation is performed with initial conditions with the event-by-event fluctuation, shock-wave capturing schemes should be used to describe the hydrodynamic expansion correctly. Here we develop a fast numerical scheme for causal relativistic hydrodynamics with dissipation for analyses of relativistic high energy collisions, which is based on Ref. [1]. This shock-wave capturing scheme for solving relativistic viscous hydrodynamic equation suffers less artificial dissipative effect and is more suitable for physical viscosity analyses, compared to SHASTA, Kurganov-Tadmor (KT) and rHLLE schemes which are mainly used in current analyses based on hydrodynamic models. Using the relativistic viscous hydrodynamic model first we evaluate the viscosity effect in collective flow such as elliptic flow, triangular flow and higher harmonics. In particular, we investigate the time evolution of them and discuss the relation between the initial geometry and final states. [1] M. Takamoto and S. Inutsuka, J. Comput. Phys. 230 (2011), 7002.Speaker: Prof. Chiho Nonaka (Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI) and Department of Physics, Nagoya University)
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Systematic Investigation of Partonic Collectivity through Centrality Dependence of Elliptic Flow of Multi-strange Hadrons in Au+Au collisions at 200 GeV in STAR 20mOne of the main goals of the STAR experiment at Relativistic Heavy Ion Collider (RHIC) is to study the properties of the QCD matter at extremely high energy and parton densities, created in the heavy-ion collisions. Understanding the partonic collectivity through the measurement of elliptic flow ($v_{2}$) of multi-strange hadrons ($\phi$, $\Xi$ and $\Omega$) is believed to be a sensitive way to characterize the system created in the heavy-ion collisions. Multi-strange hadrons freeze-out close to the quark-hadron transition temperature predicted by lattice QCD. They also have small hadronic interaction cross sections. Hence, the multi-strange hadrons are expected to provide information from the partonic stage of the evolution in heavy-ion collisions. Furthermore, the multi-strange hadron anisotropic flow in heavy-ion collisions when compared to those from $K_{s}^{0}$ and $\Lambda$, single strange valence quark carrying hadrons, will be useful for understanding the collective dynamics of the strange quarks. In this presentation we will present the new results of elliptic flow of multi-strange hadrons ($\phi$, $\Xi$ and $\Omega$ ) in Au+Au collisions at$\sqrt{s_{NN}}$= 200 GeV, using a high statistics data set collected in 2010 by the STAR experiment. Centrality dependence measurements of multi-strange hadron elliptic flow allow systematic investigation on how partonic collectivity is developed across different sizes of collision system. These results will be compared with the elliptic flow measurements of light hadrons $\pi^{\pm}$, $K^{\pm}$, $p(\bar{p})$, $K^{0}_{S}$ and $\Lambda (\bar{\Lambda})$ . The centrality evolution of the number of quark scaling of $v_{2}$ at the intermediate $p_{T}$ will be presented. The effect of re-scattering at the late hadronic stage on elliptic flow will be addressed using the $\phi$ and $p$ $v_{2}$ measurements at the low transverse momentum ($p_{T}$).Speaker: Mr NASIM MD (Variable Energy Cyclotron Centre)
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Parallel 3B: Jets (Chair S. Mioduszewski) Palladian
Palladian
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Understanding LHC jets in the light of RHIC data 20mHard probes are a cornerstone in the ongoing program to determine the properties of hot and dense QCD matter as created in ultrarelativistic heavy ion collisions. The first two runs at the LHC have resulted in a wealth of measurements of both reconstructed jets and single inclusive high P_T hadrons, opening new kinematic windows and offering high statistics. Yet on first glance, several observations are counter-intuitive and seem to contradict results from the RHIC high P_T program. I present a combined analysis of high P_T hadronic observables at RHIC and LHC and reconstructed jets at LHC in a framework testing a large number of theoretical models for both medium evolution and shower medium interactions against the systematics of the data. I demonstrate how a consistent picture of shower-medium interaction emerges from the combined results and explain where and why results appear counter-intuitive. In particular, I discuss the role of jet measurements in constraining models critically and suggest measurements sensitive to the gaps in our knowledge.Speaker: Thorsten Renk (University of Jyväskylä)
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Jet structure in 2.76 TeV Pb–Pb collisions at ALICE 20mTo capture the full dynamics of the mechanisms of energy loss of hard partons in their passage through the dense medium created in Heavy Ion Collisions, jet reconstruction is required. In this analysis we explore the radiation pattern of jets in Pb–Pb collisions at sqrt(s_NN) = 2.76 TeV and compare it to that of baseline pp jets at the same collision energy. Di-jets are selected by requiring a high-pt (’trigger’) fragment back-to-back with respect to the jet that is studied. Then, the shape and energy distribution of those quenched jets is explored via jet-hadron azimuthal correlations and via the mapping of the energy contained in different cones with radius R around the jet axis.Speaker: Leticia Cunqueiro (Unknown-Unknown-Unknown)
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Jet shapes in pp and PbPb collisions at the CMS Experiment 20mJet shape measurements are important for many applications. When measured in pp collisions they can be used to constrain generator and showering settings. When measured in PbPb collisions they can be used to probe for distortions from energy loss in the hot and dense medium. Fully unfolded jet shape measurements will be presented and compared with generator expectations in 7 TeV pp collisions, corresponding to an integrated luminosity of 36$pb^{-1}$. In addition, jet shape measurements in PbPb collisions will be presented and compared with observations in 2.76 TeV pp collisions to probe for the effects of suppression from the medium. The full PbPb data set collected in 2011 is analyzed, corresponding to an integrated luminosity of 150$\mu b^{-1}$. The jets are reconstructed with the anti-kT clustering algorithm by utilizing particle-flow objects with a radius parameter R=0.7 and R=0.3.Speaker: Pelin Kurt (Vanderbilt University (US))
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Jet fragmentation and jet properties in 2.76 TeV Pb+Pb collisions using the ATLAS Detector at LHC 20mThe recent measurements of jet suppression at LHC indicate a presence of "jet quenching" -- strong energy loss of energetic jets in hot and dense QCD medium which has been already observed at RHIC experiments. We present a measurement of jet properties which sheds more light on the mechanism of jet energy loss. We will discuss the results of measurement of longitudinal, and transverse structure of jets, as well as the spectra, and multiplicities of charged particles constituting jets. The measurement has been performed using 158 ub^-1 of lead-lead collision data provided at a nucleon center-of-mass energy of 2.76 GeV by the Large Hadron Collider and collected by the ATLAS Detector during November and December 2011.Speaker: Martin Rybar (Charles University (CZ))
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Jet fragmentation functions in PbPb and pp collisions at 2.76 TeV with CMS 20mThe jet fragmentation function of inclusive jets with pT > 100 GeV/c in PbPb collisions is measured for reconstructed charged particles with pT > 1 GeV/c within the jet cone. A data sample of PbPb collisions collected in 2011 at a center of mass energy of √sNN =2.76 TeV corresponding to an integrated luminosity of Lint = 129 μb−1 is used. The results for PbPb collisions as a function of collision centrality are compared to reference distributions based on pp data collected at the same collision energy. For the most central collisions a significant rise of the PbPb/pp fragmentation function ratio for the softest fragmentation products with pT < 3 GeV/c is observed.Speaker: Frank Ma (Massachusetts Inst. of Technology (US))
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Medium-induced soft gluon distribution inside a jet 20mThe new studies of heavy ion collisions performed at the LHC have shown the necessity to improve our understanding of parton propagation and gluon emission in the presence of a hot QCD medium. In particular, the ability to measure jets in heavy ion collisions implies that, in order to fully understand jet quenching phenomena, we must go beyond leading parton energy loss and attempt to describe how the jet structure is modified by the presence of the quark-gluon plasma. In this spirit, we study in-medium jet evolution by considering the multiple emission of soft gluons, for which the formation time is much smaller than the size of the medium. This separation of scales implies that one can consider the multiple emissions as independent and ordered in time, therefore allowing for a probabilistic interpretation where the parton shower is built as a classical branching process.Speaker: Fabio Dominguez (IPhT Saclay)
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Parallel 3C: Electro-Weak Probes (Chair J. Kapusta) Diplomat
Diplomat
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Thermal dileptons in high-energy heavy ion collisions with 3+1D relativistic hydrodynamics 20mThe penetrating nature of dileptons makes them suitable probes to explore the properties of the strongly-interacting medium created in relativistic nuclear collisions. This study investigates thermal dilepton production using MUSIC (a Monotone Upstream-centered Scheme for Ion Collisions): a 3+1D hydrodynamic simulation with or without shear viscosity. We utilize dilepton emission rates that are derived from in-medium hadronic spectral functions, and from pQCD. In addition to the invariant mass and momentum distributions, the elliptic flow of lepton pairs is calculated, and the effects of a finite shear viscosity coefficient are also analyzed. We present results appropriate for measurements by the PHENIX and STAR collaborations, and make predictions for the LHC.Speaker: Gojko Vujanovic (McGill University)
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Dielectron measurements by PHENIX using the HBD 20mMeasurements of lepton pair spectra are a crucial tool to map out the evolution of the hot dense matter created in ultra-relativistic heavy ion collisions. At low pair mass, direct photons and low mass vector mesons are the main center of interest. Interpretation of lepton pair production rates in excess of expectations from hadronic decays observed by PHENIX and how the data constrains theoretical models on thermalization and chiral symmetry restoration is a hotly debated topic. At intermediate and high mass, the di-electron spectrum has been used by PHENIX to measure cross sections of open charm and open bottom, as well as Quarkonium suppression with implications for color screening and recombination. Due to the small signal to background ratio, measurement of the dielectron spectrum, especially at low mass, is very challenging. In PHENIX, the background results mainly from random combinations of electron positron pairs from uncorrelated sources, mostly $\pi^0$ Dalitz decays and photon conversions. The Hadron Blind Detector (HBD) was developed to address this issue. The HBD accomplishes this by tagging and rejecting tracks from conversions and $\pi^0$ Dalitz decays. It was successfully operated in RHIC run years 2009 to 2010, where Au+Au and reference p+p data sets were taken. We will present the dielectron results from the analysis of these data sets.Speaker: Dr Ermias Atomssa (Stony Brook University)
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Di-electron differential cross section in Au+Au collisions at different beam energies at STAR 20mDi-leptons serve as clean and bulk penetrating probes to study the properties of the strongly interacting hot and dense medium created in heavy ion collisions. They are produced in all stages of the heavy-ion collisions and are not affected by strong interactions, hence can probe the entire evolution of the collision. Di-lepton production in the low mass range ($M_{ll}<1.1$ GeV/$c^{2}$) allows the study of vector meson in-medium properties, an observable possibly connected to chiral symmetry restoration. In the intermediate mass region ($1.1<M_{ll}<3.0$ GeV/$c^{2}$), di-lepton measurements serve as a tool to extract the medium thermal radiation, which provides direct information on the temperature of the early system. Quantitative studies on these properties require systematic measurements of di-lepton production yields as well as elliptic flow as a function of invariant mass and transverse momentum ($p_T$). An extension of these studies to energy and centrality dependent measurements offer crucial information on how the system properties evolve with collision energies and system sizes. The STAR experiment, with its large and full azimuthal acceptance, clean electron identification over a wide momentum range and low material environment, is very well suited to carry out systematic studies on di-lepton production. In the years 2010 and 2011, more than one billion events were taken in 200 GeV Au+Au collisions and several hundred million events were recorded at lower energies by the STAR experiment. In this presentation, results from di-electron mass spectra as a function of $p_T$ and centrality as well as the dependence of elliptic flow on invariant mass in 200 GeV Au+Au collisions will be presented. The results on mass, width, dN/dy, $p_{T}$ spectra of $\omega$ and $\phi$ mesons will be reported. The first STAR results of di-electron mass spectra and $p_T$ distributions at midrapidity for Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 39 and 62.4 GeV will be presented. These distributions will be compared to model calculations of in-medium vector and thermal radiation contributions to infer medium properties.Speaker: Dr Huang Bingchu (Brookhaven National Lab)
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Jet-Tagged Back-Scattering Photons For Quark Gluon Plasma Tomography 20mWe investigate the correlations of photons produced by back scattering of fast partons in quark gluon plasma with their away‐side jets. Back scattering with photon emission, or jet‐photon conversion, was originally proposed as a novel source of photons in Phys. Rev. Lett. 90, 132301 (2003). The unique appeal of this photon source lies in the fact that its photons carry information about both the medium via a T^2 log 1/T dependence of the yield and about the energy loss of partons before the back scattering occurs. Attempts to identify this source in experiment through inclusive direct photon spectra or direct photon v_2 at intermediate PT at RHIC have been inconclusive so. We show that the capability to measure jets in coincidence with photons at the upgraded STAR or SPHENIX experiment, or at one of the LHC experiments, offers a unique opportunity to identify back scattering photons at large photon momenta. Jet‐triggered back‐scattering photons can be distinguished from bremsstrahlung through their strong correlation with the given trigger ET, and from prompt hard photons through the energy loss of their parent parton. We demonstrate with leading and next‐to-leading order calculations that jet‐triggered direct photon spectra and nuclear modification factors in nuclear collisions as a function of photon PT show a distinct feature around the trigger ET due to back‐scattering photons. The height and width of this structure are correlated with the medium temperature and parton energy loss spectrum, respectively.Speaker: Prof. Rainer Fries (Texas A&M University)
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Measurement of direct photons in pp and Pb-Pb collisions with ALICE 20mDirect photons are an important probe in diagnosing the highly excited state of nuclear matter created in heavy-ion collisions: They allow access to various stages of the collision including the initial state. The ALICE detector is equipped with two high resolution electromagnetic calorimeters and a central tracking system that make it well suited to study direct photon production at low and intermediate p_t. In addition to classical calorimeter measurements the low p_t regime can be targeted via the measurement of photon conversion products by the ALICE TPC with high tracking efficiency. In this talk the analysis of direct photon production in pp (at sqrt(s) = 7 TeV) and Pb-Pb (at sqrt(s_NN) = 2.76 TeV) collisions is presented. The inclusive photon and neutral pion spectrum is measured via photon conversions in the ALICE setup. From the neutral pion yield a decay photon cocktail is deduced. The signal is obtained by calculating the double ratio (gamma/pi0)/(gamma_decay/pi0). Implications on the search for a direct photon excess at low p_t will be discussed.Speaker: Martin Rudolf Wilde (Westfaelische Wilhelms-Universitaet Muenster (DE))
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Parallel 3D: Pre-Equilibrium & Initial State (Chair K. Eskola) Empire
Empire
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Studies of the nuclear stopping power in PbPb collisions at 2.76 TeV with CMS 20mThe energy flow at very high pseudorapidity in PbPb collisions is sensitive to the very low-x components of the nuclear wave-function. The CASTOR calorimeter extends the pseudorapidity coverage of CMS to -6.6, which is only 1.4 units away from the beam rapidity. A comparison of the centrality dependence of forward energy flow to that at lower pseudorapidities can shed light on the gluon saturation at low-x. This problem can also be approached by a direct comparison of PbPb and pp energy flow in the forward region. This analysis is based on data taken in 2010. The energy flow in the pseudorapidity range of -5.2 to -6.6 has been measured for 2.76 TeV PbPb collisions over a wide range of centrality and also for minium bias pp collisions. These data are compared to energy-flow measurements for pseudorapidities between -5.2 and +5.2. The very large angular coverage of the CMS detector allows for a test of limiting fragmentation of energy flow, and for an estimate of nuclear stopping. Finally, these data are compared to predictions of hydrodynamic models and microscopic event generators.Speaker: Clemens Wohrmann (KIT - Karlsruhe Institute of Technology (DE))
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Highly-anisotropic hydrodynamics in 3+1 space-time dimensions and the early thermalization puzzle 20mRecently formulated model of highly-anisotropic and strongly dissipative hydrodynamics is used in 3+1 dimensions to study behavior of matter produced in ultra-relativistic heavy-ion collisions. We search for possible effects of the initial high anisotropy of pressure on the final soft-hadronic observables. We find that by appropriate adjustment of the initial energy density and/or the initial pseudorapidity distributions, the effects of the initial anisotropy of pressure may be easily compensated and the final hadronic observables become insensitive to early dynamics. Our results indicate that the early thermalization assumption is not necessary to describe hadronic data, in particular, to reproduce the measured elliptic flow v2. The complete thermalization of matter (local equilibration) may take place only at the times of about 1–2 fm/c, in agreement with the results of microscopic models. Work based on recent publications: 1. Highly-anisotropic hydrodynamics in 3+1 space-time dimensions, Radoslaw Ryblewski, Wojciech Florkowski, arXiv:1204.2624 2. Projection method for boost-invariant and cylindrically symmetric dissipative hydrodynamics in 3+1 space-time dimensions. Wojciech Florkowski, Radoslaw Ryblewski, Phys.Rev. C85 (2012) 044902 3. Highly-anisotropic and strongly-dissipative hydrodynamics with transverse expansion. Radoslaw Ryblewski, Wojciech Florkowski, Eur.Phys.J. C71 (2011) 1761 4. Highly anisotropic hydrodynamics -- discussion of the model assumptions and forms of the initial conditions. Radoslaw Ryblewski, Wojciech Florkowski Acta Phys.Polon. B42 (2011) 115 5. Non-boost-invariant motion of dissipative and highly anisotropic fluid. Radoslaw Ryblewski, Wojciech Florkowski, J.Phys.G G38 (2011) 015104 6. Highly-anisotropic and strongly-dissipative hydrodynamics for early stages of relativistic heavy-ion collisions. Wojciech Florkowski, Radoslaw Ryblewski Phys.Rev. C83 (2011) 034907Speakers: Michael Strickland (Gettysburg College), Wojciech Florkowski (Institute of nuclear Physics, Krakow)
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Azimuthal angular correlations in two-particle production in proton-nucleus collisions 20mDi-hadron azimuthal angular correlations in the forward rapidity region of deuteron-nucleus collisions at RHIC show a disappearance of the away side peak with centrality and transverse momentum. This can be understood, in the Color Glass Condensate (CGC) formalism, to be due to multi-gluon exchanges between the projectile and target. We show that CGC formalism predicts a similar disappearance of the away side peak in the prompt photon-hadron azimuthal angular correlations. We make detailed predictions for transverse momentum and centrality dependence of this disappearance in deuteron-gold collisions at RHIC and proton-nucleus collisions at the LHC.Speaker: Jamal Jalilian-Marian (Baruch College)
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Cold Nuclear Matter Effects in 200 GeV d+Au Collisions at PHENIX 20mWhile the study of the quark-gluon plasma has been the primary focus of the RHIC experiments, much work has also been done to understand so-called cold nuclear matter (CNM) effects through $d$+Au collisions where no hot plasma is produced. Effects such as nuclear shadowing, Cronin enhancement, and initial-state parton energy loss, among others, are not only interesting in their own right, but have direct implications on QGP-related measurements in $A+A$ collisions. Recently PHENIX has measured CNM effects at midrapidity in $\sqrt{s_{NN}}$ = 200 GeV $d$+Au collisions. Measurements of reconstructed jets reveal the centrality dependence of both jet suppression and broadening of the away-side jet. Meanwhile, single electrons from heavy flavor decays exhibit enhancement over a broad $p_T$ range and increasing with centrality. These results will be presented and compared to our present understanding of CNM effects to see if simultaneous constraints on nuclear shadowing, initial state energy loss, and Cronin effects can be found. The centrality dependence of the nuclear modification, for which there is no a priori model, will be examined in the context of available theoretical models of CNM effects, including the EPS09 nuclear-modified parton distribution functions.Speaker: Baldo Sahlmueller
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Jet probes of cold and hot QCD matter 20mParton energy loss in the hot QCD medium will manifest itself not only in leading hadron spectra but also in reconstructed jet productions in high-energy nucleus-nucleus collisions. With its more differential power full jets in heavy-ion collisions can then provide excellent tools to study the properties of the QGP and impose constraints on different parton energy loss models. With this motivation, we investigate the cold nuclear matter(CNM) effects on jet productions in high-energy nuclear collisions at LHC with the NLO perturbative QCD. The nuclear modifications for dijet angular distributions, dijet invariant mass spectra, dijet transverse momentum spectra and dijet momentum imbalance due to CNM effects are calculated by incorporating EPS, EKS, HKN and DS parametrization sets of parton distributions in nucleus. It is found that dijet angular distributions and dijet momentum imbalance are insensitive to the initial-state CNM effects and thus provide optimal tools to study the final-state hot QGP effects such as jet quenching. Furthermore we present the results and predictions at NLO for productions of the single, double and tagged jets in relativistic heavy-ion collisions by including parton energy loss effect in the QGP and the CNM effects. We demonstrate how an enhanced di-jet transverse momentum imbalance in central Pb+Pb reactions at the LHC, recently measured by the ATLAS and CMS experiments, can be derived from these results. We show quantitatively that a significant fraction of this enhancement may be related to the ambiguity in the separation between the jet and soft background medium and point to a suite of measurements that can help build a consistent picture of parton shower modification in heavy ion collisions at the LHC.Speaker: Prof. Ben-Wei Zhang (Central China Normal University)
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Gravitational collapse and holographic thermalization 20mA remarkable result from heavy ion collisions at the Relativistic Heavy Ion Collider and Large Hadron Collider is that, shortly after the collision event, the quark-gluon plasma produced behaves as a nearly ideal liquid. Understanding the dynamics responsible for such rapid "hydroization" is a challenge using traditional perturbative field theory. In recent years holography has emerged as a powerful tool to study non-equilibrium phenomena, mapping the dynamics of certain quantum field theories onto the dynamics of semi-classical gravity. Via holography, the production of quark-gluon plasma maps onto the process of gravitational collapse and black hole formation, with the relaxation of the black hole's gravitational field encoding hydroization of the dual quark gluon plasma. Thermalization of the quark-gluon plasma is encoded in the thermalization of the black hole's Hawking radiation. I will describe several processes which mimic heavy ion collisions and present results for both hydroization and thermalization times and mechanisms.Speaker: Paul Chesler (MIT)
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Poster Viewing Regency 1/3 and Ambassador
Regency 1/3 and Ambassador
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Coffee Break 30m Bird Cage & Regency Gallery
Bird Cage & Regency Gallery
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Parallel 4A: Global & Collective Dynamics (Chair P. Sorenson) Regency 2/3
Regency 2/3
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Deviation from quark number scaling of the anisotropy parameter v2 of pions, kaons, and protons in Au+Au collisions at 200 GeV 20mThe number of quark ($n_q$) scaling, which is manifested as $v^{hadron}_{2}(p_T) \approx n_q*v_2(p_T/n_q)$, is an approximate scaling that comes from the addition of the valence quark momenta at hadronization. The observation of $n_q$ scaling has been claimed that a partonic matter with quark-like degrees of freedom and significant collectivity has been generated in heavy ion collisions~\ref{1,2}. However, there are several theoretical considerations that suggest that the $n_q$ scaling should be violated in certain conditions. For example, the contribution of sea quarks and gluons have been shown to affect the $n_q$ scaling in the models including higher Fock states. And models that consider recombination between "thermal" and "shower" partons predict centrality dependent deviations from $n_q$ scaling. Understanding the limits of the recombination domain is important in relation to viscous hydrodynamics and the extraction of the shear viscosity over entropy density ($\eta/s$) from the data, as well as for developing a unified approach in describing jet energy loss and high $p_T$ $v_2$. Searches for deviations from $n_q$ scaling are also important for the low-energy scan program at RHIC as they have been considered as a signature of the transition between sQGP formation and a hadronic system. In this talk, we will report on high-statistics measurements of the second order Fourier coefficient $v_2$ for identified pions, kaons and protons, which extend to relatively high $p_T$ around 6 GeV/c. Comparisons with published measurements of $K^{0}_{S}$ and $\Lambda$ are shown for the different centralities. With these new measurements, the $p_T$ limits and centrality dependence of the $n_q$ scaling deviations are being carried out in PHENIX. [1]V. Greco, C. M. Ko, and P. Levai, Phys. Rev. Lett. 90, 42 202302 (2003). 43 [2] D. Molnar and S. A. Voloshin, Phys. Rev.Lett. 91, 44 092301 (2003).Speaker: Dr shengli huang (PHENIX Collaboration)
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Measurement of dipole flow associated with initial geometry fluctuations in Pb-Pb collisions with the ATLAS detector 20mA study of the dipole flow (v_1) associated with initial geometry fluctuations is presented using the 2010 Pb-Pb data. This analysis involves a systematic decomposition of the first order Fourier coefficient of the two-particle correlation into a dipole flow component and a global momentum conservation component. The dipolar flow is extracted as function of pT (0.5-10 GeV), centrality (0-50%) and pseudorapidity (|eta|<2.5). The magnitude of the extracted global momentum conservation component is used to estimate the effective size of the system that conserve momentum as a function of centrality. These results are compared with recent model calculations and their implications on the initial dipole asymmetry are discussed.Speaker: Jiangyong Jia (Brookhaven National Laboratory (BNL)-Unknown-Unknown)
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Baryon anomaly in heavy-ion collisions and colour correlations in QGP 20mA baryon anomaly – an increase baryon-to-meson production ratio at intermediate transverse momenta in heavy-ion collisions when compared to proton–proton collisions – is observed at RHIC and the LHC. This effect is usually explained by recombination of constituent quarks during QGP hadronisation, or as a consequence of a strong radial flow developed during the heavy-ion collision. In this contribution, a different mechanism to favour baryon-over-meson production is proposed: when hadrons are formed in the recombination of nearby quarks and antiquarks, only colour-singlet combinations can be chosen. Hadron formation, in particular the probability to create baryons or mesons, depends on the distribution of colour charges among quarks. If the distribution is random – a reasonable assumption for Quark–Gluon Plasma (QGP) – the baryon-to-meson ratio is nearly twice higher than in the situation where quark colours are pre-arranged to obtain a white hadron in the combination of nearest quarks and antiquarks. The correlation of colour charges in the QGP also influences the distance over which recombination occurs. A study of the dependencies of the baryon-to-meson ratio and of the size of the recombination domain on the colour-correlation configuration will be presented.Speaker: Karel Safarik (CERN)
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Midrapidity antibaryon-to-baryon ratios in pp and Pb-Pb collisions measured by the ALICE experiment 20mThe ALICE Experiment features low material budget and high resolution tracking, which allow for precise measurements of charged particle production. The measurement of the antibaryon to baryon ratios ($\bar{B}$/B), in particular, probes the baryon transport and the degree of baryon stopping in high energy collisions, providing insight into the collision dynamics and the structure of baryons. In this talk, we discuss the measurement of diferent $\bar{B}$/B ratios ($\bar{p}/p, $\bar{\lambda}/\lambda$, $\xi^+/\xi^-$, $\omega^+/\omega^-$) in pp collisions at \sqrt{s} = 0.9, 2.76, and 7 TeV and in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV, as a function of charged particle multiplicity, rapidity and transverse momentum. Results from pp and Pb-Pb collisions are presented and compared to models.Speaker: Michal Broz (Comenius University (SK))
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Late Result - Ds RAA from ALICE 20mThe measurement of heavy-flavour production provides insights on the properties of the high-density QCD medium created in heavy-ion collisions. In particular, the comparison of charm production in pp and in Pb-Pb collisions allows to study the mechanism of in-medium energy loss of heavy quarks. Furthermore, since strange quarks are abundant in the medium, the relative yield of D+s mesons with respect to non-strange charm mesons (D0 and D+) is predicted to be largely enhanced if in-medium hadronization is the dominant mechanism for charm hadron formation in the low momentum region. We will present the measurement of the D+s production in pp collisions at sqrt{s} = 7 TeV and in Pb-Pb collisions at sqrt{s_NN} =2.76 TeV performed with the ALICE detector at central rapidity through the exclusive reconstruction of the hadronic decay channel D+s --> Phi pi+ --> K+K-pi+. The ratios between the yields of D+s and non-strange D mesons as a function of the transverse momentum will be shown for both pp and Pb-Pb collisions.Speaker: Gian Michele Innocenti (Universita e INFN (IT))
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Parallel 4B: Jets (Chair N. Armesto) Palladian
Palladian
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Jet-medium interactions in Pb-Pb collisions 20mPrevious experimental measurements from nuclear collisions have indicated modifications of jets by interaction with the medium created in the collision. Observables from particle correlations in the ALICE detector continue to provide access to key properties of the hot deconfined nuclear matter. New results from two- and three-particle number and transverse momentum correlations are presented. Specifically, correlation function properties are characterised as a function of transverse momentum and centrality and for different charge combinations. Fourier decompositions are performed, the jet-like peak is characterised, and identified particle ratios are studied in the jet-like peak and compared to those in the bulk. These results suggest strong modifications of the peak shape and particle ratios in central collisions, compared to proton-proton or peripheral data. Model comparisons are included to assist interpretation of these results.Speaker: Jason Glyndwr Ulery (Johann-Wolfgang-Goethe Univ. (DE))
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Study of jet fragmentation with particle correlations in Pb-Pb collision at 2.76 TeV by ALICE 20mA high-$p_{T}$ jet suppression first observed at RHIC has been reported also at the LHC. The ALICE collaboration has recently reported an observation of an enhanced intra-jet yield of charged particles associated with the high-\pt{} trigger particle ($I_{\rm AA}$) in central \pbpb\ collisions at \snn=2.76 \tev\ which may be also interpreted as a hint of the modification of the fragmentation function due to induced gluon radiation. In order to study further the nature of the intra-jet correlation yield enhancement an analysis of the jet-fragmentation transverse momentum was performed. Modification of this distribution with the centrality of the collision will be presented. A possible path length dependency of the induced radiation is studied using a comparison of the two-particle correlation for different orientations of the trigger particle with respect to the event plane and comparing the jet-fragmentation transverse momentum distribution measured in different event-by-event anisotropy classes.Speaker: Filip Krizek (Helsinki Institute of Physics (FI))
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Measurements of the Correlation between Jets and the Reaction Plane in STAR at RHIC 20mThe relationship between jet properties and the underlying geometry of the medium produced in heavy ion collisions can be explored through a measurement of the correlation between the axes of reconstructed jets and the reaction plane (defined as jet $v_2$). Such a measurement provides information on the pathlength dependence of medium-induced parton energy loss as well as biases in jet-finding methods. In addition, an estimate of jet $v_2$ is necessary for background-subtraction in jet-triggered correlation analyses, which are used to study medium-induced jet shape modification. However, jet $v_2$ measurements are complicated by biases in the event plane calculation due to the presence of the jet, leading to an overestimation of jet $v_2$. In order to reduce the artificial jet-event plane bias, we utilize detectors at forward pseudorapidity ($\eta$), such as the Forward Time Projection Chambers located at $2.5 < |\eta| < 4$ and the Zero Degree Calorimeter Shower Maximum Detectors at $|\eta| > 6.3$, to determine the event plane when measuring $v_2$ of reconstructed jets at mid-rapidity ($|\eta| < 1$). We present first results of jet $v_2$ measurements in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions in STAR and their implications.Speaker: Alice Ohlson (Yale University)
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Neutral meson production in pp and Pb-Pb collisions at the LHC measured with ALICE 20mIdentified hadron spectra are considered to be sensitive to transport properties of strongly interacting matter produced in high-energy nucleus-nucleus collisions. We present measurements of $\pi^0$ and $\eta$ mesons at mid-rapidity in a wide transverse momentum range in pp and Pb-Pb collisions at LHC energies measured with the ALICE detector. The mesons are reconstructed via their two-photon decays by two complementary methods, using the electromagnetic calorimeters and the central tracking system for photons converted to electron-positron pairs on the material of the inner ALICE barrel tracking detectors. The spectrum and the nuclear modification factor ($R_{AA}$) of the $\pi^0$ production measured in Pb-Pb collisions at different collision centralities show a clear pattern of strong suppression with respect to pp collisions. The azimuthal anisotropy ($v_{2}$) of the $\pi^0$ production is consistent with $v_{2}$ for other hadron species. Comparison of the ALICE results on neutral mesons with those of lower-energy experiments is discussed.Speaker: Dmitri Peresunko (National Research Centre Kurchatov Institute (RU))
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Parallel 4C: Electro-Weak Probes (Chair D. D'Enterria) Diplomat
Diplomat
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Measurement of isolated direct photons in lead-lead collisions at 2.76 TeV with the ATLAS detector 20mDirect photons are a powerful tool to study heavy ion collisions. Their production rates provide access to the initial state PDFs, which are expected to be modified by nuclear effects. They also provide a means to calibrate the expected energy of jets that are produced in the medium, and thus are a tool to probe the physics of jet quenching more precisely both through jet rates and fragmentation properties. The ATLAS detector measures photons with its hermetic, longitudinally segmented calorimeter, which gives excellent spatial and energy resolution, and detailed information about the shower shape of each measured photon. This gives powerful rejection against the expected background from neutral pions coming from jets. Rejection against jet fragmentation products is further enhanced by isolation criteria, which can be based on calorimeter energy or the presence of high pT tracks. First results on the rates of isolated direct photons from approximately 140 µb-1 of lead-lead data will be shown, as a function of transverse momentum, pseudorapidity and centrality, and their rates compared to expectations from perturbative QCD.Speaker: Iwona Grabowska-Bold (AGH Univesity of Science and Technology (PL))
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Inclusive isolated photons in pp and PbPb collisions at 2.76 TeV with CMS 20mFinal data on isolated photon production will be presented, measured in both pp and PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV with the CMS detector at the LHC. The isolated photon transverse energy (ET) spectra, covering the pseudorapidity range |eta| < 1.44 and transverse energy ET > 20 GeV, are found to be in good agreement with next-to-leading-order perturbative QCD predictions. The measured isolated photon RAA, with a reference based on pp data, is consistent with unity for all PbPb collision centralities.Speaker: George Stephans (Massachusetts Inst. of Technology (US))
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Measurements of W and Z boson production in Pb+Pb collisions at 2.76 TeV with the ATLAS detector. 20mCollisions of lead nuclei at the LHC allow study of the deconfined phase of QCD matter at unparalleled temperatures and energy densities. The use of leptonic observables is particularly appealing as a consequence of their electroweak nature, allowing them to traverse the strongly-coupled medium essentially unaffected. W and Z bosons, observed through their semi-leptonic decay channels, may serve as a proxy for investigating phenomenological processes associated with particle interactions in the QCD medium as well as exploring hitherto unattainable regions of nuclear PDFs. The yields of these bosons in heavy ion collisions can be used for sensitive tests of binary scaling. This presentation will describe measurements of the W boson using single muon decay, and measurements of Z->ee and Z->mumu, both performed with nearly 150 ub-1 of collision data collected at a center-of-mass energy per nucleon pair sqrt(s_NN)=2.76 TeV with the ATLAS detector during the 2011 heavy ion run.Speaker: Jiri Dolejsi (Charles University (CZ))
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Z and W boson production in PbPb collisions at 2.76 TeV with CMS 20mThe Compact Muon Solenoid (CMS) is fully equipped to measure leptonic decays of electroweak probes in the high multiplicity environment of nucleus-nucleus collisions. Electroweak boson production is an important benchmark process at hadron colliders. Precise measurements of W and Z production in heavy-ion collisions can help to constrain nuclear PDFs as well as serve as a standard candle of the initial state in PbPb collisions at the LHC energies. The inclusive and differential measurements of the Z boson yield in the muon decay channel will be presented, establishing that no modification is observed with respect to next-to-leading order pQCD calculations, scaled by the number of incoherent nucleon-nucleon collisions. Measurements of the yield of W to $\mu \nu$ decays as a function of centrality and the W charge asymmetry as a function of rapidity show no modifications beyond the expected effect of isospin when compared to pp collisions.Speaker: Lamia Benhabib (Ecole Polytechnique (FR))
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Parallel 4D: Pre-Equilibrium & Initial State (Chair T. Ludlam) Empire
Empire
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Multigluon correlations in the color glass condensate 20mMultiparticle correlations, such as the "ridge" effect in pp and AA collisions and forward dihadron correlations in pA collisions, are an important probe of the strong color fields that dominate the initial stages of a heavy ion collision. We argue that the Color Glass Condensate framework provides the most natural way to understand them. We describe recent progress in understanding two-particle correlations in the dilute-dense system, e.g. in forward dihadron production in deuteron-gold collisions. This requires computing the energy dependence of higher point Wilson line correlators from the JIMWLK renormalization group equation. We find that the large Nc approximation used so far in the phenomenological literature is not very accurate. On the other hand a Gaussian finite Nc approximation is a surprisingly close to the full result.Speaker: Tuomas Lappi (U)
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Effect of longitudinal fluctuation in event-by-event (3+1)D hydrodynamics 20mHadron spectra and elliptic flow in high-energy heavy-ion collisions are studied within a (3+1)D ideal hydrodynamic model with fluctuating initial conditions given by the AMPT Monte Carlo model and compared to experimental data. Fluctuation in the initial energy density comes from not only the coherent soft interaction of overlapping nucleons but also the number of mini-jets within each binary nucleon collision. Mini-jets produced via semi-hard parton scatterings are assumed to be locally thermalized through a Gaussian smearing and give rise to fluctuation in rapidity distribution along the longitudinal direction. The longitudinal fluctuation is found to lead to sizable reduction of elliptic flow at large transverse momentum.Speaker: Long-Gang Pang (l)
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Imprinting quantum fluctuations on hydrodynamic initial conditions 20mThe precise value of the QGP kinematic shear viscosity eta/s is a question of intense topical interest. Viscous hydrodynamic simulations are a tool for extracting this information from experiment. The key observables are the anisotropic flow coefficients v_n which (i) can be measured very precisely and (ii) are very sensitive to eta/s which controls the "conversion efficiency" v_n/ecc_n for turning initial fireball eccentricities of harmonic order n into final flows of the same harmonic order. Both ecc_n and v_n fluctuate strongly from collision to collision. These event-by-event fluctuations have a key influence on the measurements [1] and must be properly taken into account when extracting eta/s. Until recently, most initial-state models accounted only for the shape and density fluctuations arising from the fluctuating positions of the nucleons in the colliding nuclei. This leads to fluctuations in the location of the newly produced matter, and thus of the initial energy density profile of the expanding fireball and its eccentricities ecc_n, but does not account for additional quantum fluctuations in the quark and gluon fields inside the nucleons that lead to fluctuating numbers of secondary particles per nucleon-nucleon interaction. Several recent papers have addressed the implementation of these quantum fluctuations in the hydrodynamic initial conditions for the expanding collision fireball. Starting from the Monte Carlo Kharzeev-Levin-Nardi (MC-KLN) model for generating fluctuating initial profiles for the gluon saturation momentum Q_sat(x_T) in the transverse plane, we have developed a Monte Carlo algorithm that uses a Gaussian Random Field (GRF) generator [2] to generate a distribution of gluonic energy densities centered at the value corresponding to the field Q_sat(x_T), but fluctuating around this profile with the two-point covariance function derived in [3] from the Glasma model. To ensure that the energy density is everywhere positive the GRF is mapped to an appropriate negative binomial distribution (NBD) with the same variance. NBD fluctuations have been recently shown to arise naturally from the Glasma model and to describe the measured multiplicity distributions in pp collisions at the LHC. The resulting density profile features ``hot spots" as in the MC-KLN model overlaid with a fluctuating field texture characterized by an intrinsic length scale 1/Q_sat(x_T). We show that inclusion of these additional gluonic quantum field fluctuations leads to only a small (few percent) increase of the initial eccentricities ecc_n in central collisions and to almost negligible effects at larger impact parameters. These findings disagree with some of the results reported in [4], and we will discuss possible origins for this discrepancy. Our results imply that an earlier extraction of the QGP shear viscosity from a combined analysis of elliptic and triangular flow data from Pb-Pb collisions at the LHC [5] is robust. References [1] Zhi Qiu and U. Heinz, ``Event-by-event shape and flow fluctuations of relativistic heavy-ion collision fireballs,'' Phys. Rev. C84, 024911 (2011). [2] X. Emery and C. Lantuejoul, ``TBSIM: A computer program for conditional simulation of 3-dimensional Gaussian random fields via the turning bands method," Computers and Geosciences 32, 1615 (2006). [3] B. Muller and A. Schafer, ``Transverse energy density fluctuations in the Color Glass Condensate Model,'' arXiv:1111.3347 [hep-ph]. [4] B. Schenke, P. Tribedy and R. Venugopalan, ``Fluctuating Glasma initial conditions and flow in heavy ion collisions,'' arXiv:1202.6646 [nucl-th]; F. Gelis, T. Lappi and L. McLerran, ``Glittering Glasmas,'' Nucl. Phys. A 828, 149 (2009); A. Dumitru and Y. Nara, ``KNO scaling of fluctuations in pp and pA, and eccentricities in heavy-ion collisions,'' Phys. Rev. C85, 034907 (2012). [5] Z. Qiu, C. Shen and U. Heinz, ``Hydrodynamic elliptic and triangular flow in Pb-Pb collisions at sqrt(s)=2.76ATeV,'' Phys. Lett. B707, 151 (2012).Speaker: Mr J. Scott Moreland (Duke University)
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The spectrum of quantum fluctuations and space-time evolution in the little bang 20mWe outline significant recent progress in a program to include quantum corrections to the evolution of the classical color fields produced in high-energy ultra-relativistic heavy ion collisions. Previous work in this direction for a scalar \phi^4 theory [1] has now been extended to QCD. Leading contributions from unstable quantum modes can be resumed to all loop orders and expressed in terms of a gauge invariant spectrum of initial quantum fluctuations, which has been computed recently [2]. These fluctuations play a key role in decoherence of the high occupancy fields, and in their possible isotropization and flow, and in the matching of this initial dynamics to hydrodynamic flow, thereby potentially eliminating a big source of uncertainty in hydrodynamic simulations. We report on progress in the 3+1-D numerical computations implementing these pre-equilibrium dynamics. [1] K.~Dusling, T.~Epelbaum, F.~Gelis and R.~Venugopalan, %``Role of quantum fluctuations in a system with strong fields: Onset of hydrodynamical flow,'' Nucl.\ Phys.\ A {\bf 850}, 69 (2011); T.~ Epelbaum and F. Gelis, %``Role of quantum fluctuations in a system with strong fields: Spectral properties and Thermalization,'' Nucl.\ Phys.\ A {\bf 872}, 210 (2011). [2] K.~Dusling, F.~Gelis and R.~Venugopalan, %``The initial spectrum of fluctuations in the little bang,'' Nucl.\ Phys.\ A {\bf 872}, 161 (2011).Speaker: Raju Venugopalan (Brookhaven National Laboratory)
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Forward azimuthal correlations in 200 GeV p+p and d+Au collisions at STAR 20mThe proton gluon distribution function increases rapidly with decreasing x at fixed $Q^{2}$, but cannot increase indefinitely as x goes to 0. Gluon saturation is expected at a low x value when gluon recombination balances gluon splitting. The nuclear (with atomic mass number A) gluon distribution is approximately $A^{1/3}$ larger than the nucleon gluon distribution function at the same x [1]. STAR is sensitive to x between 0.001 and 0.02 for the nuclear gluon distribution via di-jet measurements with calorimeter subsystems covering -1 < eta < 4. The STAR collaboration has measured forward $\pi{0}$-$\pi{0}$ correlations and forward+mid-rapidity correlations in p+p and d+Au collisions at $\sqrt{s}=200GeV$. The suppression of the away-side peak observed in forward-forward correlations in central d+Au collisions is consistent with the CGC expectation [2,3]. Such suppression does not appear in the forward+mid-rapidity correlations. The Endcap Electromagnetic Calorimeter (EEMC) at STAR covers pseudo-rapidity between 1.08 and 2, providing the opportunity to probe gluons at intermediate x via forward+near-forward correlations. Azimuthal correlations between $\pi{0}$ in the Forward Meson Spectrometer (FMS) and jet-like clusters in the EEMC are sensitive to the nuclear gluon distribution in 0.003<x<0.02 region. Together with the forward+forward correlations and forward+mid-rapidity correlations, we will be able to determine the sharpness of the transition along x from a dilute parton gas to the expected CGC state at low $Q^{2}$. In this talk, we will focus on FMS-$\pi^{0}$ + EEMC-jet-like-cluster azimuthal correlations in p+p and d+Au collisions. The impact from underlying-event contributions to the jet-like clusters and effective p+Au results, via a deuteron-beam-facing neutron tag, will be discussed as well. [1] H. Kowalski, D. Teaney, Phys. Rev. D 68, 114005, 2003. [2] E. Braidot, arXiv:1005.2378, 2010. [3] J. L. Albacete, C. Marquet, Phys. Rev. Lett , 105,162301, 2010.Speaker: Xuan Li (Shandong University)
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Poster Viewing Regency 1/3 and Ambassador
Regency 1/3 and Ambassador
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Lunch time and afternoon free for discussions and excursions 5h 20m
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Plenary IVA: Real & Virtual Photons (Chair: T. Nayak) Regency 2/3
Regency 2/3
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Award of Zimanyi Award (Chair M. Gyulassy) 15m
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Coffee Break 40m
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Plenary IVB: Quarkonia, Real & Virtual Photons (Chair Y. Schutz) Regency 2/3
Regency 2/3
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Quarkonia Discussion 15m
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Lunch 1h 15m Blue Room
Blue Room
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Parallel 5A: Hadron Thermodynamics and Chemistry (Chair R. Stock) Regency 2/3
Regency 2/3
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Identified charged hadron production at the LHC with the ALICE experiment 20mIdentified particle spectra are a basic observable to understand the behaviour of the matter created in high-energy heavy-ion collisions. The transverse momentum distributions of identified hadrons contain informations about the transverse expansion of the system and constrain the freeze-out properties of the matter created. The ALICE experiment has very good particle identification capabilities over a broad pT-range. Particles are identified using the energy loss signal in the Inner Tracking System and Time Projection Chamber detectors, complemented with the information from the Time of Flight detector to identify hadrons up to pT ∼ 5 GeV/c. In this contribution the results for identified pions, kaons and protons in pp collisions at 0.9 and 7 TeV center-of-mass energy and heavy-ion collisions at 2.76 TeV center-of-mass energy will be presented. These results are compared with other identified particle measurements obtained by the ALICE experiment, and discussed in terms of the thermal and hydrodynamical pictures. The status of extensions of this analysis, with the study of identified particles as a function of event-by-event flow in Pb-Pb collisions and as a function of multiplicity in pp collisions, will also be discussed.Speaker: Leonardo Milano (Universita e INFN (IT))
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The statistical model in Pb-Pb collisions at the LHC 20mWe investigate, using the newest LHC data, the energy dependence of hadron production within the framework of the statistical hadronization model. The data are confronted with predictions based on extrapolation from lower (RHIC) energies. While the yields of hadrons made from light (u,d,s) quarks generally exhibit little change apart from the overall increase in multiplicity, a characteristic energy dependence is observed for J/psi production. This feature is well described by statistical generation of J/$\psi$ mesons at the phase boundary, as predicted in [1,2]. We also search for possible deviations from the statistical picture in the yields of (anti-)baryons and light (anti-)nuclei. [1] P. Braun-Munzinger, J. Stachel, Phys. Lett. B 490 (2000) 196. [2] A. Andronic, P. Braun-Munzinger, K. Redlich, J. Stachel, Nucl. Phys. A 789 (2007) 334; Phys. Lett. B 652 (2007) 259.Speaker: Peter Braun-Munzinger (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
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Strange hadrons and resonances in Pb-Pb collisions at sqrt_NN = 2.76 TeV with ALICE experiment at LHC 20mThe ALICE experiment at the LHC has measured the production of strange hadrons and resonances in Pb-Pb and pp collisions at unprecedentedly high beam energies. The study of strange hadrons and resonances helps us to understand the medium properties and its evolution at dierent stages. We will present the pT spectra and yields at mid-rapidity for strange hadrons (, labda, xi, omega, their anti-particles and K0S ) and resonances ( and K0 ) for different collision centrality. The results from Pb-Pb collisions at psNN = 2.76 TeV will be presented and compared to corresponding results from pp collisions and lower energy measurements. Baryon to meson ratios, resonance to non-resonance particle ratios relative to pp collisions will be shown as a function of collision centrality and compared with the results at low energies. Finally, the spectral shapes will also be discussed in terms of hydrodynamical-inspired models.Speaker: Subhash Singha (Department of Atomic Energy (IN))
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Beam Energy Dependence of Strange Hadron Production from STAR at RHIC 20mStrange hadron production is sensitive to parton dynamics in nucleus-nucleus collisions. In particular, the strange quark production rate and its subsequent evolution in the dense partonic medium depend on the beam energy and the net baryon density. We will present STAR measurements of $K^{0}_{s}$, $K^{\pm}$, $\phi$, $\Lambda$, $\Xi$, and $\Omega$ at mid-rapidity from Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, and 39 GeV from the RHIC Beam Energy Scan (BES) program. We will report the strangeness enhancement through the ratios $K/\pi$, $\Lambda/\pi$, $\phi/\pi$ and $\Xi/\pi$, and strangeness equilibration as a function of beam energy at RHIC. Nuclear modification factors and baryon to meson ratios will be discussed to understand recombination and parton energy loss mechanisms. Further, the particle ratios will be compared to ultra relativistic quantum molecular dynamics, hadron string dynamics, statistical hadronization models and SPS measurements. Implications on partonic vs. hadronic dynamics at low beam energies will also be discussed.Speaker: Dr Xiaoping Zhang (Tsinghua University)
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(Anti) matter and hyper-matter production at the LHC with the ALICE experiment 20mThe excellent particle identification capabilities of the ALICE experiment allow the studies of (anti) matter and hyper-matter production. (Anti) deuterons, tritons, 3He and 4He as well as the corresponding antinuclei can be cleanly identified based on their specific energy loss in the Time Projection Chamber and velocity information in the Time-Of-Flight detector. The (anti) hyper-triton signal can be extracted from the study of its mesonic decay (3_lambda_H -> 3He + pion) via the topological identification of secondary vertices. The (3He, pion) invariant mass spectrum will be shown, and the measurement of production yield will be provided. Transverse momentum (pt) spectra of (anti) nuclei along with their production yield and mean pt will be presented. In addition to this, searches for even lighter hyper-matter systems, i.e. lambda-lambda and lambda-n bound states will be discussed. The results will also be compared with the expectations from the thermal and coalescence models.Speaker: Benjamin Doenigus (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
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Beam Energy Dependence of Hypertriton Production and Lifetime Measurement at STAR 20mThe hyperon-nucleon(Y-N) interaction is of great physical interest because it introduces a new quantum number strangeness in nuclear matter. It is predicted to be the decisive interaction in some high-density matter systems, such as neutron stars [1]. RHIC, the Relativistic Heavy Ion Collider, provides an ideal laboratory to study Y-N interaction because hyperons and nucleons are abundantly produced at high energy nucleus-nucleus collisions. The lifetime and decay modes of the hypertriton, the lightest hypernucleus, which consists of a proton, a neutron and the lightest hyperon Lambda, and the antimatter hypertriton discovered at RHIC[2], provide valuable insights into the Y-N interaction. The strangeness population factor S3, defined as $\frac{{^3_\Lambda}H/^{3}He}{\Lambda/p}$, is a good representation of the local correlation between baryon number and strangeness[2]. It is predicted that S3 has a different behavior in QGP and pure hadron gas[3,4] thus can be used as a tool to distinguish Quark-Gluon Plasma (QGP) from a pure hadronic phase. The RHIC beam energy scan program in 2010-2011 allowed STAR to collecte data from Au+Au collisions over a broad range of energies. This provides an opportunity to study the beam energy dependence of S3. In addition, due to the beam energy independence of our lifetime measurement method, with increased statistics of present datasets, an improved result of lifetime measurement of hypertriton can be obtained. In this talk, the hypertriton analysis results for Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39 and 200 GeV will be presented. With the excellent particle identification of Time Projection Chamber, we are able to reconstruct $^{3}_{\Lambda}H$($^{3}_{\bar{\Lambda}}\bar{H}$) via its two-body decay channel to $^{3}He$ and $\pi^{-}$($\overline{^{3}He}$ and $\pi^{+}$). The combined $^{3}_{\Lambda}H$ plus $^{3}_{\bar{\Lambda}}\bar{H}$ raw yield is about 600 and its significance can reach 9.5$\sigma$. With this increased statistics, our lifetime measurement will be presented and the beam energy dependence of S3 will also be discussed. [1]J. M. Lattimer, M. Prakash, Science {\bf304}, 536 (2004) [2]B. I. Abelev {\it et al.}(STAR Collaboration), Science {\bf328}, 58 (2010) [3]S. Zhang {\it et al.}, Phys. Lett. B. {\bf 684}, 224 (2010) [4]J. Steinheimer {\it et al.}, arXiv:1203.2547v1Speaker: Ms Yuhui Zhu (Shanghai Institute of Applied Physics)
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Parallel 5B: QCD at Finite Temperature and Density (Chair F. Karsch) Palladian
Palladian
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Photon production in hot QCD plasmas at NLO and two-to-three processes 20mWe determine the photon production rate at next to leading order, i.e. through order $g^2 m_D/T$. At leading order, photon production is determined by three processes: hard two-to-two collisions, collinear bremsstrahlung, and quark-conversions, i.e. a process where the incoming quark transfers almost all of its momentum to the produced photon and the final state quark is soft. At NLO, wider angle bremsstrahlung must be treated carefully, and the LPM suppressed leading order rate smoothly matches onto two-to-three processes. Similarly, asymmetric bremsstrahlung, when the photon carries a large momentum fraction of the incoming momentum and the final state quark is soft, must be smoothly matched onto the quark conversion process present at leading order. We carefully include these rates without double counting to determine the full photon production rate at NLO.Speaker: Derek Teaney (Stony Brook University)
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Transverse Momentum Broadening in Weakly Coupled Quark-Gluon Plasma 20mWe calculate P(k_perp), the probability distribution for an energetic parton propagating for a distance L through a medium to pick up transverse momentum k_perp, for a medium consisting of weakly coupled quark-gluon plasma. We use full or HTL self-energies in appropriate regimes, resumming each in order to find the leading large-L behavior. We estimate the jet quenching parameter and compare to results in the literature. And, we compare P(k_perp) at weak coupling to the P(k_perp) expected from holographic calculations that presume the quark-gluon plasma to be strongly coupled at all length scales. We find that the weak coupling and strong coupling results need not differ greatly at modest k_perp, but we find that P(k_perp) must be parametrically larger in a weakly coupled plasma than in a strongly coupled plasma at large enough k_perp. By looking for rare large-angle deflections of the jet resulting from a parton produced initially back-to-back with a hard photon, experimentalists can find the weakly coupled quark and gluon short-distance constituents of the strongly coupled liquid quark-gluon plasma, much as Rutherford found the nuclei within atoms or Friedman, Kendall and Taylor found the quark within nucleons.Speaker: Mindaugas Lekaveckas (MIT)
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Electric and baryonic charge fluctuations from lattice QCD 20mWe calculate electric and baryonic charge fluctuations on the lattice. Results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with temporal extent of N_tau=6,8,12. Higher cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which is arising due to a critical point of QCD in the chiral limit. Considering cumulants up to the 6th order, we observe that they generically behave as expected from universal scaling laws, which is quite different from cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be directly compared to the experimental measurements. Such a comparison will unambiguously relate the QCD transition temperature that has been determined on the lattice with, the freeze out temperature of the heavy ion collision at LHC and the 200 GeV RHIC run.Speaker: Dr Christian Schmidt (Universitaet Bielefeld)
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Lattice QCD thermodynamics in the presence of the charm quark 20mWe present our estimate for the charm quark's contribution to the equation of state and to the fluctuations of conserved charges. Our results are based on simulations with dynamical charm at physical quark masses. We also address the question, to what extent staggered simulations are reliable. We give comparisons with the Wilson formulation as well as with results using dynamical overlap fermions.Speaker: Dr Claudia Ratti (Torino University)
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Freeze-out conditions from lattice QCD 20mTraditionally the freeze-out conditions in the heavy-ion collision experiments are obtained by comparing the experimentally measured hadron yields with that from the statistical hadron resonance gas model. In this talk we will present how the freeze-out chemical potentials and the freeze-out temperature can be obtained in a model independent way from ab-initio lattice QCD calculations by utilizing observables related to conserved charge fluctuations. We will show that the freeze-out strangeness and electric charge chemical potentials can be fixed by imposing strangeness neutrality and isospin asymmetry constraints in the lattice QCD calculations. Further, we will present how the freeze-out baryon chemical potential and the freeze-out temperature can be determined by comparing lattice QCD results for various ratios of conserved charge susceptibilities with the corresponding ratios of moments of conserve charge fluctuations that are currently being measured by the STAR experiment. A comparison of the freeze-out parameters obtained from the lattice QCD calculations with that from the hadron resonance gas model will also be presented.Speaker: Swagato Mukherjee (Brookhaven National Laboratory)
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The QCD Equation of State with 2+1 flavors of Highly Improved Staggered Quarks 20mThe physics of the Quark-Gluon Plasma (QGP), currently explored experimentally in heavy-ion collisions, is non-perturbative for temperatures below approximately 1 GeV. One of the fundamental properties of the QGP, the Equation of State, is a subject of extensive studies in lattice QCD. The lattice QCD Equation of State is now an essential requirement for the correct hydrodynamic modeling of heavy-ion collisions. Lattice QCD provides first-principle calculations with physical results recovered in the continuum limit. Thus, understanding of the discretization effects is of great importance. I report on recent progress by the HotQCD collaboration in studying the 2+1 flavor Equation of State on lattices with the temporal extent Nt=6, 8, 10 and 12 in Highly Improved Staggered Quarks (HISQ) discretization scheme. In the low-temperature phase, where the Hadron Resonance Gas (HRG) model is expected to be a good approximation, a comparison of HRG and lattice results is also presented. Comparisons with Equation of State calculations with different fermion actions will also be discussed.Speaker: Alexei Bazavov (B)
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Parallel 5C: High pt and Jets (Chair B. Cole) Diplomat
Diplomat
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Systematic Monte-Carlo studies of dijets at the LHC and RHIC 20mRecent results from Pb+Pb collisions at the LHC have shown evidence of dramatic medium modification of di-jets. Although asymmetric di-jets are also seen in p+p collisions, di-jets with a large energy asymmetry are found much more often in Pb+Pb collisions. E.g., events with a 200 GeV leading jet and a 80 GeV subleading jet were frequently observed. The increase in the average energy asymmetry is believed to be caused by in-medium energy loss that arises from the interaction of the colored jet constituents with the hot deconfined matter formed is the collision. The modified di-jets provide a means to study the nature of the high energy interactions of this deconfined matter. The observed di-jet suppression has been quantified in terms of the asymmetry A_j, the ratio of the difference between the two jet energies to their sum. It is not a priori clear that this is the observable best suited to extract information about the modification of the di-jets and the nature of their interactions with the deconfined medium. Understanding the sensitivity of di-jet observables to properties of the deconfined medium and to experimental factors is vital if they are to become a useful tool for jet tomography of hot QCD matter. We have examined the response of the di-jet asymmetry and other di-jet observables to variations in the jet modification mechanism and to variations of the observables. We present a systematic study of di-jet suppression at RHIC and the LHC using the VNI/BMS parton cascade. VNI/BMS is a jet+medium Monte-Carlo code which provides a controllable testbed with sufficient complexity to model jet modification without confounding results with fluctuations from hydrodynamics and hadronization. We consider the medium modification of the di-jet asymmetry A_j and the energy distribution within the di-jets (jet shape). Di-jets are examined under the modification of: the jet transport coefficient qhat; the path length of leading and sub-leading jets; cuts on the jet energy distributions; jet cone angle and the jet-medium interaction mechanism and the strong coupling constant. We find that, while the jet asymmetry and jet shape are similarly sensitive to the in-medium path length, the jet-shape is more sensitive to the nature of the interaction with the medium and the value of q-hat than the jet asymmetry.Speaker: Christopher Coleman-Smith (Duke Physics)
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Production of Charged Pions, Kaons, and Protons in 2.76 TeV Pb-Pb Collisions at high p_t measured with the ALICE Experiment. 20mThe main tracking detector in the central barrel ($|\eta|<1$) of the ALICE experiment is the Time Projection Chamber. In addition to charged particle tracking it provides particle identification (PID) through the measurement of the specific energy loss, $dE/dx$. At low momentum ($p < 1$ GeV/c), pions, kaons, and protons can be cleanly separated. Thanks to the relativistic rise of the $dE/dx$, the relative yield of pions, kaons, and protons can also be extracted statistically at higher momenta, $p > 3$ GeV/c. In this talk, spectra for charged pions, kaons, and protons from pp collisions at $\sqrt{s} = 2.76$ TeV and Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV for $3 < p_{t} < 20$ GeV/c will be presented, and the nuclear modification factor $R_{AA}$ will be derived. The evolution of $R_{AA}$ with collision centrality and transverse momentum will be discussed, and compared to unidentified charged particles, $K_{s}^{0}$ , $\Lambda$, and theoretical predictions.Speaker: Antonio Ortiz Velasquez (Lund University (SE))
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Charged particle spectra and nuclear modification factor in lead-lead collisions at 2.76 TeV with the ATLAS detector at the LHC. 20mThe measurement of charged particle spectra in heavy ion collisions is a direct way to study properties of hot and dense matter created in these interactions. The centrality dependence of the spectral shape is an important tool to understand the energy loss mechanism. The ATLAS detector at the LHC accumulated 150µb-1 of lead-lead data at 2.76 TeV per nucleon-nucleon pair. Due to the excellent capabilities of the ATLAS detector, and its stable operation in 2010 and 2011 heavy ion physics runs, these data allow measurements of the charged particle spectra and their ratios in different centrality bins over a wide range of transverse momenta and pseudorapidity.Speaker: Petr Balek (Charles University (CZ))
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R_CP and R_AA Measurements of Identified and Unidentified Charged Particles at High p_T in Au+Au Collisions at 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV in STAR 20mThe suppression of high $p_{T}$ hadrons in 200 GeV Au+Au collisions at RHIC has been seen as a signature for a partonic medium being formed. The evolution of this key QGP signature is a powerful tool for studying the QCD phase structure in the RHIC Beam Energy Scan (BES). In this talk, we will present measurements of identified $\pi^{\pm}$, $K^{\pm}$, and $p(\bar{p})$ and unidentified charged particles in Au+Au collisions at $\sqrt{s_{NN}}=$7.7, 11.5, 19.6, 27, 39, and 62.4 GeV. We will report nuclear modification factors $R_{CP}$ and $R_{AA}$ where published p+p references are available. These results offer insight into the $\sqrt{s_{NN}}$ dependence of high $p_{T}$ suppression in nuclear collisions.Speaker: Evan Sangaline (UC Davis)
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Strange hadrons at intermediate and high transverse momentum in p+p, d+Au, Cu+Cu and Au+Au collisions at 200 GeV measured with PHENIX detector 20mThe hadrons containing strange quark(s) are among the most interesting probes of the hot and dense matter produced in heavy ion collisions at Relativistic Heavy Ion Collider (RHIC). While p+p collisions are used as a baseline for comparison with heavier collision systems and provide a cross check for pQCD calculations, d+Au collisions are used to study cold nuclear matter effects for mesons and baryons and their dependence on particle mass and flavor. Heavy ion collisions provide an insight into effects of quark recombination and jet quenching. Experimental measurements reveal if strange particles are suppressed at high transverse momentum ($p_T$) similarly to light hadrons and if the quark recombination mechanisms boosts strange hadron production at intermediate $p_T$. The PHENIX experiment provides excellent capabilities to measure particles with strangeness content over a wide $p_T$ range using a combination of different analysis techniques. In this talk we present the latest PHENIX result on production of K$^\pm$, K$_s$, K*, $\phi$ and $\Lambda$ which considerably extend the $p_T$ range for p+p, d+Au, Cu+Cu and Au+Au collisions at \sqrt{s_{NN}} = 200 GeV. The nuclear modification factors are obtained for d+Au and heavy ion collisions at different centralities. These systematic study advance the understanding of the strange meson and baryon production and their difference from light hadrons.Speaker: Dr Prashant Shukla (Bhabha Atomic Research Centre (IN))
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A Running Coupling Explanation of the Surprisingly Transparency of the QGP at LHC 20mThe CUJET1.0 Monte Carlo Jet Energy loss model is applied to predict the jet flavor, centrality and density dependence of the nuclear modification factor $R_{AA}$ and the elliptic flow $v_2$ at RHIC and LHC. Running coupling effects due to combined $x$, $k_\perp$ and $q_\perp$ evolution are included for the first time in the dynamical DGLV opacity expansion framework and are shown to provide a natural dynamical QCD tomographic solution to the surprising transparency$^1$ of the quark gluon plasma produced at LHC as suggested by $p_T>10$ GeV $R_{AA}$ data from ALICE, ATLAS, and CMS. (Ref: 1: W.H.Horowitz et al, NPA872(2011)265, A.Buzzatti et al, PRL108(2012)022301, B.Betz et al arXiv:1201.0281 [nucl-th])Speaker: Alessandro Buzzatti (Columbia University)
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Parallel 5D: New Theoretical Developments (Chair B. Sinha) Empire
Empire
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Calculating Jet Transport Coefficients in Lattice Gauge Theory 20mThe in-medium modification of a hard jet is reformulated to consider the process of a hard parton propagating through a finite sized QCD medium, held at a fixed high temperature and vanishing chemical potential. The process is factorized into a hard part representing the propagation and scattering of the parton, and a soft part representing the non-perturbative color field experienced by the jet in the medium. A series of such non-perturbative, soft, transport coefficients are identified, and formulated in terms of well defined operator products. These operator products are then expanded in a series of power suppressed local operators, which are then evaluated non-perturbatively using quenched lattice gauge theory.Speaker: Dr Abhijit Majumder (Wayne State University)
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A Non-AdS/CFT bound on eta/s 20mHydrodynamics predicts long-lived sound and shear waves. Thermal fluctuations in these waves can lead to the diffusion of momentum density, contributing to the shear viscosity and other transport coefficients. Within viscous hydrodynamics in 3+1 dimensions, this leads to a positive contribution to the shear viscosity, which is finite but inversely proportional to the microscopic shear viscosity. Therefore the effective infrared viscosity is bounded from below. The contribution to the second-order transport coefficient $\tau_\pi$ is divergent, which means that second-order relativistic viscous hydrodynamics is inconsistent below some frequency scale. We estimate the importance of each effect for the Quark-Gluon Plasma, finding them to be minor if $\eta/s = 0.16$ but important if $\eta/s = 0.08$.Speaker: Paul Romatschke (FIAS Frankfurt)
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Coupling dependence of jet quenching in hot strongly-coupled gauge theories 20mPrevious top-down studies of jet stopping in strongly-coupled QCD-like plasmas with gravity duals have been in the infinite 't Hooft coupling limit $\lambda \to \infty$. They have found that, though a wide range of jet stopping distances are possible depending on initial conditions, the maximum jet stopping distance $\ell_{\rm max}$ scales with energy as $E^{1/3}$ at large energy. But it has always been unclear whether the large-coupling and high-energy limits commute. We use the string $\alpha'$ expansion in AdS-CFT to study the corrections to the $\lambda{=}\infty$ result in powers of $1/\lambda$ by assessing the effects of all higher-derivative corrections to the supergravity action for the gravity dual. We find that sometimes $\lambda=\infty$ results can be trusted for jet stopping, but other times the expansion in $1/\lambda$ breaks down.Speaker: Peter Arnold (University of Virginia)
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Shining a Gluon Beam through Quark-Gluon Plasma 20mA holographic calculation of the quenching of a beam of gluons with typical momenta q shining through strongly coupled quark-gluon plasma shows that such a beam is attenuated rapidly over a distance of order q^{1/3} (pi T)^{-4/3} as it propagates at the speed of light, shedding trailing sound waves with momenta of order (pi T). At larger and larger q, the trailing sound wave becomes less and less prominent. The outward-going beam of gluon radiation itself shows no tendency to spread in angle or to shift toward larger wavelengths, even as it is completely attenuated. In this regard, the behavior of the beam of gluons that we analyze is reminiscent of the behavior of jets produced in heavy ion collisions at the LHC that lose a significant fraction of their energy without appreciable change in their angular distribution or their momentum distribution as they plow through the strongly coupled quark-gluon plasma produced in these collisions. However, we know that quark-gluon plasma must be weakly coupled at short enough distance scales. This means that even if jet quenching typically occurs as in a strongly coupled plasma, there should be rare events in which a hard parton is scattered by a larger angle, picking up significant transverse momentum.Speaker: Krishna Rajagopal (MIT)
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Color decoherence of jets in Heavy Ion Collisions 20mThe recent jet measurements at RHIC and the LHC have challenged the heavy-ion community to a better understanding of jet fragmentation in the presence of the Quark-Gluon-Plasma (QGP). Jet fragmentation in vacuum is well described by perturbative QCD and is characterized by color coherence effects that lead to the angular ordering of successive branchings along the jet. To investigate the alteration of color coherence in jets in the QGP we study the radiation pattern of a color-correlated quark-anti-quark antenna which is in fact the building block of jet evolution in vacuum. We show that in a dense medium the onset of coherence is governed by the hardest scale induced by the presence of the medium. In a medium of length $L$ and transport coefficient $\hat q$ this can either be the typical transverse momentum broadening of the gluon in the medium, $\sqrt{\hat q L}$, or the inverse of the size of the antenna as probed by the medium, namely $r_\perp^{-1}=(\theta_{qq} L)^{-1}$, where $\theta_{qq}$ is the opening angle of the antenna. Therefore, for $k_\perp<max(\sqrt{\hat q L}, r_\perp^{-1})$ we obtain complete decoherence of the antenna; for larger momenta color coherence is restored. We expect the transition from color decoherence to coherence to play an important role in in-medium jet fragmentation.Speaker: Dr Yacine Mehtar-Tani (IPhT-Saclay)
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Temperature dependence of the shear viscosity in the semi-QGP 20mAn effective theory for the region near the critical temperature, the "semi"-QGP, has been developed. In QCD, this is dominated by the partial ionization of color, up to temperatures about 300 MeV. Using the effective model, the temperature dependence for the ratio of the shear viscosity, to the entropy, is computed. This predicts a sharp increase in this ratio between ~ 160 MeV and ~ 300 MeV.Speaker: Dr Robert Pisarski (Brookhaven National Lab.)
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Poster Session Reception Regency 1/3 and Ambassador
Regency 1/3 and Ambassador
Posters will be displayed in the Ambassador Room and part of the Regency Room. They will be available for viewing from Tuesday to Thursday.
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"Chemical" composition of the Quark-Gluon Plasma in relativistic heavy-ion collisions 2hWe study the evolution of the quark-gluon composition of the plasma created in ultra-Relativistic-Heavy Ion Collisions (uRHIC's) employing a partonic transport theory that includes both elastic and inelastic collisions plus a mean fields dymanics associated to the widely used quasi-particle model. The latter, able to describe lattice QCD thermodynamics, implies a "chemical" equilibrium ratio between quarks and gluons strongly increasing as T -> Tc, the phase transition temperature. Accordingly we see in realistic simulations of uRHIC's a rapid evolution from a gluon dominated initial state to a quark dominated plasma close to Tc. The quark to gluon ratio can be modified by about a factor of 20 in the bulk of the system and appears to be large also in the high pT region. We discuss how this aspect, often overflown, can be essential for a quantitative study of several key issues in the QGP physics: shear viscosity, jet quenching, quarkonia suppression. Furthermore a bulk plasma made by more than 80% of quarks plus antiquarks provides a theoretical basis for hadronization via quark coalescence. Ref. [arXiv:1202.2262]Speaker: Prof. Vincenzo Greco (University of Catania)
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${\rm D^+}$ meson production in p-p and Pb-Pb collisions with the ALICE detector 2hOpen heavy flavour hadrons produced in high-energy ion collisions are an interesting tool to investigate the properties of the QCD medium, as they come from the hadronization of heavy quarks which are created in the early stage of the interaction and which experience the whole collision history. Energy loss of heavy quarks in the medium can be investigated by comparing the heavy flavour production cross sections in p-p and nucleus-nucleus collisions. The measurement of ${\rm D^+}$ production as a function of transverse momentum in p-p and Pb-Pb collisions at $\sqrt{s}_{NN}$ = 7 and 2.76 TeV respectively with the ALICE detector is presented. ${\rm D^+}$ mesons are reconstructed from their $K^- \pi^+ \pi^+$ hadronic decay that can be reconstructed in the central rapidity region using the tracking and PID detectors. Charm production cross sections in p-p collision is compared to pQCD predictions and the nuclear modification factor of ${\rm D^+}$ is presented.Speaker: Riccardo Russo (Universita e INFN (IT))
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A chiral effective theory for dilepton production in NN and AA collisions 2hIn this talk, I present an effective model based on the linear representation of the chiral U(N_f)_r x U(N_f)_l symmetry of QCD. It is demonstrated that a reasonable fit of the mass parameters and coupling constants of the model to hadron vacuum properties can be obtained. This study can contribute to answering the question about the quark content of the scalar isoscalar mesons. The model is used to investigate dilepton production in NN and AA collisions and to search for signatures of chiral symmetry restoration at nonzero temperatures and densities.Speaker: Dirk Rischke (U)
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A detailed study of open heavy flavor production, enhancement, and suppression at RHIC 2hThe flexibility of the beam species available at the Relativistic Heavy Ion Collider has enabled the PHENIX Collaboration to examine open heavy flavor production across a wide range of temperature, energy density, and system size. Charm and bottom production in $p+p$ collisions, which is dominated by gluon fusion, is largely consistent with FONLL pQCD calculations. New analysis techniques have extended the momentum coverage and provide constraints on the bottom cross section. Measurements in $d+$Au collisions exhibit a strong cold nuclear matter Cronin enhancement of electrons from $D-$mesons, which is roughly consistent with the mass-ordering observed for the lighter $\pi, K,$ and $p$ families. This also shows that the nuclear baseline for interpreting Au+Au data could be significantly modified from the $p+p$ shape. Collisions of Cu nuclei provide a crucial intermediary testing ground between the small $d$+Au collision system and the large Au+Au system, and show how the cold nuclear matter enhancement is overtaken by competing hot nuclear matter suppression as the system size increases towards the most central Au+Au collisions. The status of finalizing these results results and others will be discussed, in the context of recent measurements at RHIC and the LHC.Speaker: J. Matthew Durham (Los Alamos National Laboratory)
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A direct measure of anisotropic velocity in relativistic heavy ion collisions 2hThe radial flow parameters are important quantities in relativistic heavy ion collisions [1]. They constrain the equation of state [2] and in particular, the anisotropic parameter relates to shear viscosity [3]. They are usually extracted from the spectrum of transverse momentum by the parameterizations of Blast-wave model [4]. In the present work, we suggest a direct measure of radial velocity, i.e., microscopic average velocity of freeze-out particles in azimuthal plane. It contains three parts: average radial expansion velocity, average anisotropic velocity (the amplitude of modulation in radial expansion velocity as function of the relative angle to the reaction plane), and average thermal velocity. Using the sample of Au+ Au collisions at 200 GeV produced by AMPT with string melting model, we demonstrate that this microscopic average velocity is well fitted by two parts: an average isotropic velocity, and an average anisotropic velocity, which is azimuthal angle dependent. This form of radial velocity is the same as theoretically expected radial flow parameterization [5]. But the difference is that the average isotropic velocity contains the contributions of thermal motion. From the particle species dependence of the average isotropic velocity, we demonstrate that the heavier the mass of the particles, the smaller the isotropic velocity is. It is just the character of thermal motion. Fortunately, average thermal velocity is isotropic and therefore has no contribution toward the average anisotropic velocity. In order to confirm this, the centrality dependence of average radial velocity is presented. We find that its anisotropic part is close to zero when the collisions approach to the central ones. It shows indeed no anisotropic velocity in an ideal central collision. Moreover, we carefully extract kinetic freeze-out parameters in the same sample by fitting pt spectrum and elliptic flow using the parameterization of blast-wave model [4,6]. It is found that the average anisotropic velocity is well coincident with the anisotropic flow velocity extracted by blast-wave model. Furthermore, the centrality dependence of average anisotropic velocity is also consistent with that of extracted from the Blast-wave model. So microscopic average anisotropic velocity of final state particles is a good approximation of anisotropic flow velocity. [1] P. Huovinen, P.F. Kolb, U. Heinz, P.V. Ruuskanen , S.A. Voloshin, Phys.Lett. B 503 (2001) 58–64; Jajati K. Nayak and Jan-e Alam, Phys. Rev. C 80, 064906 (2009)；R. Arnaldi et al. (NA60 Collaboration), Phys. Rev. Lett. 100, 022302(2008); Sergei A. Voloshin, Arthur M. Poskanzer, and Raimond Snellings，arXiv: 0809.2949. [2] P. Huovinen and P. V. Ruuskanen, Ann. Rev. Nucl. Part. Sci.,2006, 56 :163；D. A. Teaney, arXiv: 0905.2433; Huichao Song, arXiv:0908.3656v1 [3] L.D.Landau, E.M. Lifschitz, Fluid Mechanics, Institute of Physical Problems, U.S.S.R. Academy of Sciences,Volume 6, Course of Theoretical Physics; Chun Shen, Ulrich W Heinz, Phys.Rev.C83:044909,2011; Wang Meijuan, Li Lin , Liu Lianshou and Wu Yuanfang, J. Phys.G: Nucl.Part.Phys: 36, 064070(2009). [4] E. Schnedermann, J. Sollfrank, and U. W. Heinz, Phys. Rev. C.1993,48, 2462-2475; W.Broniowski and W.Florkowski. Phys.Rev.Lett.87, 272302(2001). F. Retiere and M.A. Lisa, Phys. Rev. C 70 044907 (2004); [5] Arthur M. Poskanzer, J.Phys. G30 (2004) S1225-S1228; J. Adams, et al., (STAR Collaboration), Phys.Rev.C72:014904, 2005; Y. Oh, Z. W. Lin, C. Y. Ko, Phys. Rev. C , 2009, 80: 064902. [6] Ming Shao, Li Yi, Zebo Tang, Hongfang Chen et al., J. Phys. G37: 085104,2010; Zebo Tang et al.,arXiv: 1101.1912.Speaker: Prof. Yuanfang Wu (Institute of Particle Physics, CCNU, Wuhan China)
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A GEM-based continuous readout scheme for the ALICE TPC 2hThe Time Projection Chamber (TPC) is the central tracking device of the ALICE experiment, providing momentum measurement and particle identification via the specific energy loss dE/dx. The readout rate of the TPC is presently limited by the necessity to prevent ions from the amplification region of the MWPC-based readout chambers to drift back into the drift volume, which is achieved through active ion gating by operating a dedicated Gating Grid. The relevant ion drift times limit the maximum trigger rate of the TPC to about 3.5 kHz. For future running at the LHC beyond 2019, where collision rates of 50 kHz in Pb-Pb are expected, these limitations can be overcome by replacing the present MWPC-based readout chambers by a GEM readout, which provides intrinsic ion capture capability without additional gating. In this contribution the perspectives of a GEM TPC for ALICE with continuous readout are discussed and the expected performance and status of R & D will be presented.Speaker: Taku Gunji (University of Tokyo (JP))
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A novel high momentum particle identification detector for the next generation ALICE experiment 2hA high momentum particle identification detector is under discussion by the ALICE experiment at CERN as part of its plan for high luminosity data taking in the next decade. The VHMPID detector is improving on well established ring imaging Cerenkov technology by using a pressurized gas volume in a focussing geometry to minimize the radial depth of the device. In this configuration the VHMPID can be paired with existing calorimeter modules in order to enable track by track PID measurements in fully reconstructed jets. The detector is expected to achieve unambiguous K, pi, p separation in the 5-25 GeV/c momentum range. In this talk we will present the detector technology, the proposed detector layout, detailed test beam results, and selected achievable physics measurements such as particle identified fragmentation functions in vacuum (p+p collisions) and in medium (A+A collisions) and hadro-chemistry measurements in single jets as well as jet-jet and photon-jet correlations.Speaker: Austin Vincent Harton (Chicago State University (US))
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A QCD-like theory with the Z_{Nc} symmetry 2hWe propose a QCD-like theory with the Z_{Nc} symmetry. The flavor-dependent twisted boundary condition (TBC) is imposed on Nc degenerate flavor quarks in the SU(Nc) gauge theory. The QCD-like theory is useful to understand the mechanism of color confinement. Dynamics of the QCD-like theory is studied by imposing the TBC on the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model. The Z_{Nc} symmetry is preserved below some temperature Tc, but spontaneously broken above Tc. The color confinement below Tc preserves the flavor symmetry. Above Tc, the flavor symmetry is broken, but the breaking is suppressed by the entanglement between the Polyakov loop and the chiral condensate. Particularly at low temperature, dynamics of the TBC model is similar to that of the PNJL model with the standard fermion boundary condition, indicating that the Z_{Nc} symmetry is a good approximate concept in the latter model even if the current quark mass is small. The present prediction can be tested in future by lattice QCD, since the QCD-like theory has no sign problem.Speaker: Dr Yuji Sakai (RIKEN)
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A Silicon Photomultiplier (SiPM) Based Readout for the sPHENIX Upgrade 2hConceived and constructed over a decade ago, the PHENIX detector was designed to discover the Quark-Gluon Plasma (QGP). Following on this discovery,the PHENIX collaboration has embarked on a number of upgrades to study the QGP properties in detail, with the next step being a significant overhaul of the PHENIX detector called sPHENIX. sPHENIX includes upgrading the central detector with a compact solenoid, electromagnetic and hadronic calorimetry to study jets produced in p+p, p+A, and A+A collisions at RHIC. The location of the calorimetry in vicinity of the solenoid requires an optical readout that is compact and immune to magnetic fields. For this reason, the sPHENIX calorimetry will use a Silicon Photomultiplier(SiPM) based readout system for both the electromagnetic and hadronic calorimeters. In this presentation, we present the current design status and performance of the prototype analog readout for the sPHENIX calorimetry based on SiPMs.Speaker: Eric Mannel (B)
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A Study of High-pT/High-mass Dielectron Production through Trigger Combination in 200 GeV Au+Au Collisions at STAR 2hDileptons are unique probes of the strongly-coupled Quark Gluon Plasma (QGP) created in relativistic heavy-ion collisions. Compared to hadrons, leptons have little interaction with the QGP medium and can thus travel through the entire system with most of the original information intact. This feature allows us to study the properties of the medium during its space-time evolution. The low mass region (LMR, m < 1.1 GeV/c^2) is dominated by the decay of the vector mesons, in which chiral symmetry restoration in the medium can be studied. In the intermediate mass region (IMR, 1.1 < m < 3.0 GeV/c^2), the dominant dilepton sources are expected to be the thermal radiation of the QGP and the semileptonic decays of charmed mesons. Systematic measurements in both mass regions and at all pT are crucial in revealing the medium's properties. Finally, high-pT dileptons in particular allow measurements of direct photons and of spectrum enhancements in the LMR. To observe the dilepton production at high pT, it is necessary to utilize the data from the high-pT triggers in conjunction with the minimum-bias trigger. These dielectron measurements are made using data from the STAR time projection chamber, time of flight, and the barrel electromagnetic calorimeter (BEMC) at midrapidity. In this poster, we present a study on the dielectron production in 200 GeV Au+Au collisions recorded by the STAR detector in 2010 using a novel combination of the minimum-bias trigger and three high-pT triggers with different energy thresholds in the BEMC. Because the mass spectrum from each high-pT trigger is biased, we apply an effective weight to each dielectron pair based on the trigger threshold and scale factor. Finally, we combine the weighted results from all four triggers. The analysis details and associated mass spectra will be discussed.Speaker: Kurt Jung (Purdue University (US))
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A Technique for Charm and Beauty Separation via DCA Unfolding 2hThe PHENIX experiment at the Relativistic Heavy Ion Collider recently took data in p+p and Au+Au collisions with a new silicon vertex detector (VTX). This upgrade detector is capable of measuring the off-vertex decay of heavy flavor decay electrons via distance of closest approach (DCA). The resulting measured DCA distributions will be a convolution of the parent meson momenta, decay lifetimes, and yields, combined with detector irresolution and backgrounds. We will describe an algorithm to unfold the full set of DCA distributions as a function of p_{T}, thereby allowing improved extraction of the charm and beauty yields. The progress for applying this technique to the heavy ion collision VTX data set will also be shown.Speaker: Michael McCumber (University of Colorado)
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A way to acquire some current quark mass from a general relativistic effect 2hWe calculate a way to acquire some current quark mass from a general relativistic effect. For a bare quark, we model that boundary conditions on the spacetime metric can plausibly couple the value of current quark mass to the charge, via external pressure (e.g., as supplied by a background field) at sub-fm length scales. This mechanism acquires some (up to ~ 40%) current quark mass “from” the charge. To construct an approximate metric, we model a bare quark as a spherically symmetric static perfect fluid with charge, using a recent exact Maxwell-Einstein metric for the interior, out to a radius r at which the boundary condition is to match to the Reissner-Nordström metric (for spacetime external to a charged mass). At r, the model produces internal pressure, which should be matched to external pressure. For reported values of quark charges q and bare masses mq, this construction produces sub-fm radii. Although the metric at this radius differs only perturbatively from a flat spacetime, the matching condition is more significant and couples the current quark mass to the charge.Speaker: Dr Thomas Kiess (self)
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An extreme granularity electromagnetic calorimeter using monolithic pixels for future forward measurements in ALICE 2hA forward electromagnetic calorimeter (FoCal), to be placed in the pseudorapidity range of $2.5<\eta<4.5$, is being discussed as one of the upgrade plans for the LHC-ALICE experiment. One of the motivations for building such a detector is the study of direct photons, as well as correlations including photons, pions and jets in pp,pA and AA collisions at the highest LHC energies. Such measurements will require a detector of extremely high granularity, capable of discriminating photons from neutral pions at high energies. This detector will also have unique capabilities to resolve overlapping showers in a very high-multiplicity environment. A prototype of a sub-100 $\mu m$ pixel detector based on a silicon-tungsten layered structure was built in 2011. The active regions of the prototype consist of MIMOSA chips, having a thin active detecting element, and an undepleted silicon layer with readout electronics directly on top of it. Detector beam-tests have been conducted at CERN-PS and DESY to evaluate its feasibility and performance. We present an evaluation of the prototype performance, along with the first beam-test results, as well as further MIMOSA protoype developments.Speaker: Nikola for the ALICE-FoCal collaboration Poljak (NIKHEF/Univeristy of Utrecht)
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Analysis of the pi0-charged hadron correlations using ALICE EMCal 2hNeutral pion production measured with the ALICE detector in Pb-Pb collisions at the LHC is an important tool to study the properties of the hot and dense medium created in heavy-ion collisions. The neutral pion yield, obtained with the ALICE electromagnetic calorimeter in pp collisions at sqrt(s) = 2.76 and 7 TeV, as well as in Pb-Pb collisions at sqrt(s_NN) = 2.76, is analyzed in terms of x_t scaling. High-p_t neutral pions are used as trigger particles to study the momentum distribution of the associated charged particles. The latest status of the analysis in pp and Pb-Pb collisions will be presented.Speaker: Xiangrong Zhu (Central China Normal University CCNU (CN))
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Anisotropic flow in event-by-event ideal hydrodynamic simulations of √sNN=200 GeV Au+Au collisions 2hWe calculate flow observables with the NeXSPheRIO ideal hydrodynamic model and make the first comparison to the complete set of mid- rapidity flow measurements made by the PHENIX collaboration in top energy Au+Au collisions. A simultaneous calculation of v2, v3, v4, and the first event-by-event calculation of quadrangular flow defined with respect to the v2 event plane (v4{psi2}) gives good agreement with measured values, including the dependence on both transverse momentum and centrality. This provides confirmation that the collision system is indeed well described as a quark-gluon plasma with an extremely small viscosity, and that correlations are dominantly generated from collective effects. In addition we present a prediction for v5. Reference: arXiv:1203.2882Speaker: Dr Frederique Grassi (Universidade de Sao Paulo, Brazil)
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Anisotropic flow of φ meson in Pb-Pb collisions at sqrt{s_{NN}} = 2.76 TeV with the ALICE detector 2hThe $\phi$-meson flow is seen as an important observable to study hydrodynamic behavior and partonic collectivity of heavy-ion collisions. We present detailed measurements of $\phi$-meson flow in $\sqrt{s_{NN}}$=2.76 TeV Pb--Pb collisions with the ALICE detector. The results are compared to the flow of other identified particles (kaons, pions, antiprotons, lambdas, cascades ) to investigate the mass splitting and the approximate number of quark scaling.Speaker: You Zhou (Nikhef and Utrecht University (NL))
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Anisotropic optical response of dense quark matter under rotation - compact stars as cosmic polarizers - 2hQuantum vortices in the color-flavor locked (CFL) phase of QCD have bosonic degrees of freedom localized on them, called the orientational zero modes. We show that the orientational zero modes are electromagnetically charged. As a result, a vortex in the CFL phase nontrivially interacts with photons. We show that a lattice of vortices acts as a polarizer of photons with wavelengths larger than some critical length.Speaker: Mr Yuji Hirono (The University of Tokyo)
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Anomalous soft photon production from QCD vacuum polarization 2hAnomalous soft photon production beyond that predicted by standard Bremsstrahlung calculations is a ubiquitous feature in high energy processes, from e+e- to heavy ion collisions. We calculate the electromagnetic current due to the QCD vacuum polarization induced by the qq jets in e+e- annihilation using the Schwinger model, and source Maxwell’s equations with it. The predicted soft photon emission reproduces the DELPHI Collaboration’s observations in e+e- annihilation, exhibiting several times the signal expected from traditional Bremsstrahlung radiation. We will discuss the implications of our results for the soft photon production in heavy ion collisions.Speaker: Joshua Ilany (Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA)
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Antiparticle to particle ratios and identified hadron spectra for p+p collisions in sqrt(s)=62.4 GeV at STAR 2hInformation about the evolution of the system formed during the high energy p + p collisions can be obtained by investigating the charged particle ratios. The particle ratios serve as an important indicator of the collision dynamics [1]. These can be used to probe the process of hadronization in high energy collisions. In this poster, we will present measurements of mid-rapidity antiparticle to particle ratios in p + p collisions at sqrt(s)= 62.4 GeV from the STAR experiment. The charged pion and kaon particle ratios as well as the antiproton to proton ratios will be measured as a function of transverse momentum using the TPC detector. Charged hadrons will be identified by using specific ionization energy loss at the low momentum region (0.15 to 0.75 GeV) [2-3]. We will compare our results with the previous measurements made with same collision system at ISR energies [4]. Antiproton to proton ratio will be obtained after applying background corrections to the proton yields. References [1] H. Satz , Rep.Prog.Phys. 63 (2000) 151. [2] B. I. Abelev et al., [STAR Collaboration], Phys.Rev.C 79 (2009) 34909. [3] H. Bichsel, Nucl.Instrum.Meth.A vol. 562, (2006) 154-197. [4] B. Alper et al., Nucl.Phys.B 100 (1975) 237-290.Speaker: Shikshit Gupta (University of Jammu)
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Assessment of heavy-ion background fluctuations via Independent Particle Emission in full jet reconstruction measurements 2hThe main difficulty in precise and systematically controlled jet measurements in heavy-ion collisions is the correction for the soft underlying background fluctuation as well as for additional hard scatterings occurring in the nucleus-nucleus collision. To minimize non-trivial biases in jet-quenching measurements by imposing kinematical constraints on the jet fragmentation and to suppress background fluctuations requires a precise description of background fluctuations down to very low momentum. In order to avoid ambiguities in the background fluctuation estimate, caused by additional hard scatterings, especially in the inclusive jet cross-section measurement at lower jet energies, we propose a statistical correction scheme: The Independent Particle Emission Model. In this approach we characterize the soft underlying heavy-ion background fluctuations in a typical jet area via a statistical convolution of multiplicity and (mean) transverse momentum pT fluctuations. In addition higher order flow harmonics (vn) will be taken properly into account. We will present simulation studies in order to estimate the precision of the Independent Particle Emission Model. Furthermore we will discuss conceptually how this approach can be applied in data analysis and how one can assess the validity of the assumed functional form in a data driven way.Speaker: Mr Christopher Yaldo (Wayne State University)
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Azimuthal angle correlations in forward dihadron production in pA collisions 2hSingle inclusive hadron production in the forward rapidiy region in deuteron-gold collisions is well understood in the Color Glass Condensate (CGC) framework. As a complement to single inclusive spectra, detailed information is obtained with two-particle correlations. Recent measurements of the azimuthal angle correlations at RHIC have shown that there is a strong suppression of the away side peak at forward rapidities. This is easily understood in the CGC framework: the produced partons are initially back-to-back in the transverse plane, but the interaction with the nucleus causes a momentum transfer of the order of the saturation scale. In forward dihadron production the small-x structure of the nucleus is probed, implying a large saturation scale. We present on going work on calculating the dihadron correlation using the running coupling BK equation. We include the inelastic terms neglected in some of the previous literature and show that they naturally contain the double parton scattering part that has so far been treated as a separate contribution. We also use, for the first time in a phenomenological application, a Gaussian approximation of JIMWLK to go beyond the large-Nc limit.Speaker: Heikki Mäntysaari (University of Jyväskylä, Department of Physics)
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Azimuthal angular correlations between heavy flavour decay electrons and charged hadrons in pp collisions at 2.76 TeV with the ALICE experiment 2hThe measurement of heavy-flavour (charm and beauty) production in ultra-relativistic heavy ion collisions provides an important test of the parton energy loss mechanism and its predicted color charge and parton mass dependencies. The suppression of electron yields from semi-leptonic decays of D and B mesons in Pb-Pb collisions at the LHC has been observed to be large. Because of the dead-cone effect, heavy quarks are expected to loose less energy than light quarks if the dominant energy loss mechanism is gluon radiation. The suppression expected on the basis of energy loss depends on the relative contribution of D and B hadrons to the total yield. Therefore, it is important to separate these contributions. The relative contribution of beauty decays to the total electron yield from heavy flavour decays can be isolated by looking at azimuthal correlation between these electrons and charged hadrons, exploiting the different decay kinematics of D and B hadrons. In this talk, we present results on the relative beauty contribution to the heavy flavour decay electron yield and the beauty production cross section in the pt range 2.5-10 GeV/c in pp collisions at sqrt(s) = 2.76 TeV recorded in 2011 with the ALICE experiment. The results are compared to predictions from next-to-leading order perturbative QCD calculations. In addition, the status of the same analysis in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV is presented.Speaker: Deepa Thomas (University of Utrecht (NL))
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Azimuthal anisotropy harmonics in ultra-central PbPb collisions at 2.76 TeV from the CMS experiment 2hAzimuthal anisotropy harmonics have been measured in ultra-central PbPb collisions at a center-of-mass energy per nucleon pair of 2.76 TeV. Top central 0.2\% PbPb collisions have been collected using a unique trigger on total energy at forward hadronic calorimeter and total multiplicity of hits on pixel tracker by the CMS experiment during 2011 LHC PbPb run. A total of about 1.8 million events were recorded with top 0.2\% collision centrality. Fourier flow harmonics ($v_n$) are extracted from Fourier decomposition of long-range dihadron correlations as a function of particle transverse momentum. The relative ratio of different $v_n$ provides a direct constraint on the eta/s of the QGP matter, independent of the initial condition models.Speaker: Wei Li (MIT)
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Azimuthal Correlation of Charm at Large Hadron Collider 2hWe present the azimuthal correlation of charm, anti-charm pairs produced at LHC energies. We show our results for both proton on proton collision as well as lead on lead collision. An empirical model has been included to show the effect of energy loss on the correlation . Separately an effect of collective flow using blast wave model on the correlation is also shown.Speaker: Mohammed Younus (Variable Energy Cyclotron Centre)
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Background-subtraction procedure for the measurement of the elliptic flow of heavy-flavour decay electrons in ALICE 2hIn ultra-relativistic heavy-ion collisions, charm and beauty quarks are a sensitive tool to probe the flavour and mass dependence of the parton interaction with the medium created in such interactions, the Quark-Gluon Plasma. The level of thermalization of heavy quarks can be studied via the azimuthal anisotropy of their emission in the transverse plane, the elliptic flow v2, at low transverse momentum. At high pt, v2 provides insight on the path length dependence of parton energy-loss. One channel to measure the heavy-flavour v2 is semi-electronic decays of hadrons carrying a charm or a beauty quark. ALICE recorded Pb-Pb collisions at 2.76 TeV at the end of 2010 and 2011. The presented poster will focus on the method to subtract the background electron contribution in the measurement of the elliptic flow of heavy-flavour decay electrons in Pb-Pb collisions at 2.76 TeV with ALICE at mid-rapidity. The elliptic flow of inclusive electrons is measured with the event plane method. At high pt the contribution of electrons from heavy-flavour decays is expected to be dominant, whereas at low pt most electrons come from Dalitz decays of pi0 and gamma conversions in the detector material. A Monte Carlo simulation, based on the measured elliptic flow and pt distributions of the main background sources, is performed to estimate the contribution from known background electrons. The knowledge of the ratio of inclusive electrons to the known background electrons allows to subtract the background cocktail from the inclusive electron v2 and obtain the heavy flavour decay electron v2.Speaker: Bogdan Theodor Rascanu (Johann-Wolfgang-Goethe Univ.)
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Balance function studies for non–identified particles in Pb–Pb collisions at √sNN = 2.76 TeV 2hThe possible creation of a strongly interacting deconfined phase (Quark-Gluon plasma) in relativistic heavy ion collisions would be measurable in a delayed hadronization time. It was proposed to test this hypothesis via the measurement of correlations between positive and negatively charged pairs pairs as a function of rapidity, the so-called Balance functions, which was done at SPS and RHIC energies. We will present first studies of Balance functions at LHC energies with the ALICE experiment. In Pb–Pb collisions at √sNN = 2.76 TeV the width of Balance functions in pseudorapidity and azimuthal angle for non-identified charged particles shows a clear centrality dependence. In addition a comparison to other experiments (NA49, STAR) at lower c.m. energies and different models (Hijing, AMPT, Blast wave) will be presented.Speaker: Alis Rodriguez Manso (NIKHEF (NL))
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Baryon number probability distribution in the presence of the chiral phase transition 2hWe discuss the influence of the chiral phase transition on the properties of the probability distribution of conserved charges based on effective chiral models and on the Landau theory of phase transition [1]. Statistical fluctuations of the net baryon number have been regarded as a diagnostic tool of the chiral phase transition in QCD and in heavy ion collisions. Normally, they are discussed by calculating cumulants of the net baryon number in the grand canonical ensemble. Lattice QCD and effective model calculations have revealed their critical behaviors in the vicinity of the chiral phase transition. The purpose of this work is to characterize the critical behavior in terms of the baryon number probability distribution which is a measurable observable in heavy ion collisions. We show the influence of the chiral crossover transition on the net baryon number probability distribution within the Polyakov loop extended quark-meson model, in a non-perturbative approach, based on the functional renormalization group method [1]. We construct an analytically solvable model which respects relevant symmetries, based on the Landau theory, and discuss properties of the baryon number probability distribution in the presence of the phase transition. We emphasize the relationship of the probability distribution to the analytic structure of the grand canonical partition function in a complex chemical potential [2-4]. We show, through both numerical and analytic considerations, that the singular structure, which gives the divergent cumulants, leads to an interesting anomalous oscillatory behavior in the probability distribution. Our theoretical studies are relevant in heavy ion phenomenology to possibly identify the QCD phase transition and its order by measuring probability distributions of conserved charges. [1] K. Morita, V. Skokov, B. Friman and K. Redlich, to appear. [2] V. Skokov, K. Morita, B. Friman, Phys. Rev. D83, (2011) 071502(R). [3] K. Morita, V. Skokov, B. Friman and K. Redlich, ``Probing deconfinement in the Polyakov-loop extended Nambu-Jona-Lasinio model at imaginary chemical potential,'' arXiv:1111.3446 [hep-ph]. [4] K. Morita, V. Skokov, B. Friman and K. Redlich, Phys. Rev. D84 (2011) 074020. [5] K. Morita, V. Skokov, B. Friman and K. Redlich, Phys. Rev. D84 (2011) 076009.Speaker: Dr Kenji Morita (Kyoto University)
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Baryonic resonances at the LHC energies with the ALICE experiment 2hThe study of resonances production in p-p collisions provides constraints on QCD-inspired particle production models. In Pb-Pb collisions, resonances are good probes to estimate the collective properties of the fireball and may add constraints to the estimate of its lifetime. $p_T$ spectra have been measured for the baryonic resonances $\Lambdastar$, $\Sigmastar$ and $\Xistar$ using data collected by the ALICE experiment in p-p collisions at $\sqrt{s} = 7$ TeV. The spectra will be compared to QCD-inspired models such as PYTHIA and PHOJET, which in general underpredict the experimental results on the yields of strange resonances. The ratios of yields of baryonic resonances to stable particles, namely $\Sigmastar / \Lambda$, $\Lambdastar / \Lambda$ and $\Xistar / \Xi$ will be compared with both thermal models and corresponding values from previous experiments at different colliding energies. These results will serve as baseline for the forthcoming heavy-ion results. The status and prospects of the measurements of baryonic resonances in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV will be discussed.Speaker: Enrico Fragiacomo (Universita e INFN (IT))
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Beam Energy Dependent Charge Balance Functions in Heavy Ion Collisions at STAR 2hThe study of correlations between opposite sign charge pairs can provide a powerful tool to probe the properties of the quark-gluon plasma (QGP). The balance function, which measures the correlations between opposite sign charge pairs, is sensitive to the mechanisms of charge formation and the subsequent relative diffusion of the balancing charges. The study of the balance function can provide information about charge creation time as well as the subsequent collective behavior of particles. We will present charge balance function results for relative pseudorapidity and azimuthal angle from Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 to 200 GeV from the recent RHIC beam energy scan. Results from new measurements of balance function at $\sqrt{s_{NN}}$ = 19.6 and 27 GeV are added to the suite of observations. We will also present balance function results in terms of relative rapidity and Lorentz invariant momentum difference between the two particles for identified pions, kaons and protons using STAR Time Of Flight (TOF) detector. The normalized balance function width ($W$ parameter)~\cite{NA49_balance_2007} is applied to compare different experimental measurements of the width of the balance function in terms of relative pseudorapidity. UrQMD transport model calculations are also compared with data. \bibitem{NA49_balance_2007} C. Alt {\it et al.} [NA49 Collaboration], Phys. Rev. C {\bf 76}, 024914 (2007).Speaker: Hui Wang (Michigan state university)
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Bulk properties of hot QCD matter at RHIC and LHC and Universal QGP hadronization condition 2hThe short lifespan of the QCD phase at RHIC and LHC suggests fast filamenting disintegration of the supercooled QGP state of matter. The ensemble of all produced hadrons carry information about the physical properties of the disintegrating QGP. For example the energy content is obtained evaluating the energy carried by all hadrons. Considering that many of the particles have not been measured, extrapolation of their yields have decisive impact on the result of the analysis of these 'bulk' properties. We present a strategy how to obtain precise description of the available data using a maximum-parameter phase space model. Our results show that the bulk properties at RHIC and LHC are extremely similar and do not differ significantly from high energy SPS results supporting the notion that bulk QGP at hadronization is governed by the same universal hadronization conditions charactrized by a common pressure and energy density. We show that the chemical equilibrium model forcing hadron yields to equilibrate in the hadron phase fails both to describe the data and to produce consistent description of bulk properties across centrality and a wide energy domain, which we achieve.Speaker: Michal Petran (Czech Technical University (CZ))
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Can baryon stopping explain the breakdown of constituent quark scaling and proposed signals of chiral magnetic waves at RHIC? 2hAzimuthal emission spectra of various hadron species in ultra-relativistic heavy ion collisions at $\sqrt{s_{NN}} \approx $ 200 GeV exhibit a curious hierarchy at intermediate $p_t$ ($\approx 2-3$ GeV). Rather than being ordered by mass, the spectra seem to be ordered by whether the species is a baryon or meson. It is seen that when the elliptic flow $v_2$ and transverse momentum $p_T$ are both scaled by the number of quarks in each hadron, the spectra fall in line with each other [1]. This number of constituent quark (NCQ) scaling suggests a system where the relevant degrees of freedom are colored partons as opposed to hadrons: the quark-gluon plasma (QGP). Thus, a break down of this scaling as beam energy is reduced could be indicative of the QGP threshold. However, at lower energies, there is also an increase in the number of entrance-channel partons transported to mid-rapidity due to baryon stopping, which can also violate NCQ scaling, even above the QGP threshold [2]. We describe a specific pattern for the break down of the scaling that includes the observed difference in elliptic flow for positive and negative pions. \\ We also contrast baryon stopping with the Chiral Magnetic Effect (CME) [3]--an alternative model for $\pi_{+} / \pi_{-}$ flow difference--and discuss results from tests that can distinguish between them. [1] Rainer J. Fries, Vincenzo Greco, and Paul Sorensen, Coalescence Models For Hadron Formation From Quark Gluon Plasma, Ann.Rev.Nucl.Part.Sci. 58 (2008), 177–205. [2] J.C. Dunlop, M.A. Lisa, and P. Sorensen, Constituent quark scaling violation due to baryon number transport, Phys.Rev. C84 (2011), 044914. [3] Yannis Burnier, Dmitri E. Kharzeev, Jinfeng Liao, and Ho-Ung Yee, Chiral magnetic wave at finite baryon density and the electric quadrupole moment of quark-gluon plasma in heavy ion collisions, Phys.Rev.Lett. 107 (2011), 052303.Speaker: John Campbell (T)
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Can falling strings in deformed AdS geometries account for the surprising transparency of the sQGP at LHC? 2hWe present new solutions for holographic falling string models of light quark jet energy loss that suggest a linear path dependence of energy loss, dE/dx ~ x^1, without the nonlinear x^2 dependence assumed previously. This effect, combined with non-conformal deformations and higher curvature corrections of AdS geometry, is shown to be able to account for the small relative reduction of the jet-medium coupling observed via RAA(pT) at LHC in the 20-50 GeV pT region.Speaker: Andrej Ficnar (Columbia University in the City of New York)
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Centrality and pT dependence study of Dielectron Production in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at STAR 2hDilepton production has been proposed to serve as a penetrating probe for the hot and dense medium created in high-energy nuclear collisions. Their small final-state interaction cross sections, let dileptons escape the interaction region undistorted. Since dileptons originate from all stages of a heavy ion reaction, their sources vary with the kinematic phase space under consideration: In the low mass region (LMR: mass<1.1GeV/$c^{2}$), vector mesons and direct photons are the dominating source, while dileptons in the intermediate mass region (IMR:1.1<mass<3GeV/$c^{2}$) primarily stem from QGP thermal radiation at RHIC energy and semileptonic decays of charmed mesons. In the high mass region (HMR: mass>3 GeV/$c^{2}$), heavy quark decays and Drell-Yan processes contribute the most to the dilepton spectrum. Due to the time-energy correlation, the higher the dilepton pair mass, the earlier the production. Therefore the dilepton distributions, especially in the IMR and HMR, provide information on early collision dynamics in heavy ion collisions. In this talk we will present a systematic study of dielectron production in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at STAR experiment. The datasets used are nearly one billion Au+Au minibias events collected in RHIC runs year 2010 and 2011. The dielectron pair transverse momentum and centrality dependence of the invariant mass distribution will be discussed. The results will be compared to hadron decay cocktails as well as theoretical calculations on vector meson in-medium modifications and the QGP thermal radiation.Speaker: jie zhao (lbl&sinap)
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Centrality, mass and transverse momentum dependence of di-electron elliptic flow in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at STAR 2hDi-leptons are ideal probes of the strongly interacting hot and dense medium created at RHIC. They are not affected by the strong interaction once produced, therefore they can probe the whole evolution of the collision. The di-leptons spectra in the intermediate mass range ($1.1<M_{ll}<3.0$ GeV/$c^{2}$) are directly related to thermal radiation of the Quark-Gluon Plasma (QGP). In the low mass range ($M_{ll}<1.1$GeV/$c^{2}$), we can study the vector meson in-medium properties through their di-leptons decays, the observable of possible chiral symmetry restoration. It has been proposed that the elliptic flow measurements of di-leptons in different mass regions will enable us to probe the properties of medium from hadron-gas dominated to QGP dominated. In 2010 and 2011 more than one billion minimum bias events were taken. The 2$\pi$ azimuthal coverage of the newly installed time-of-flight subdetector enables the elliptic flow measurements of di-electrons. In this poster, we will report elliptic flow measurements of di-electrons from low to intermediate mass region for Au+Au collisions at 200 GeV. Differential measurements of di-electrons elliptic flow as a function of transverse momentum in different mass regions will be presented. Centrality dependence will be reported and model comparisons will also be discussed.Speaker: Xiangli Cui (U)
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Charge Asymmetry Dependency of $\pi^+/\pi^-$ Azimuthal Anisotropy in Au + Au Collisions at STAR 2hA recent theoretical study indicates that a chiral magnetic wave at finite baryon density could induce an electric quadrupole moment in the quark-gluon plasma produced in heavy ion collisions. The quadrupole deformation will lead to a difference in azimuthal anisotropy $v_2$, between positive and negative pions, and the magnitude of this difference is predicted to be proportional to net charge asymmetry. The net charge asymmetry is defined as $(N_+ - N_-)/(N_+ + N_-)$, while $N_+ (N_-)$ is the number of positive (negative) particles. STAR experiment has observed the different $v_2$ of particles and anti-particles at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV. Study on the charge asymmetry dependency of $\pi^+/\pi^-$ azimuthal anisotropy will shed light on the possible sources of the $v_2$ difference of particles and anti-particles. We present STAR's measurement of azimuthal anisotropy difference between positive and negative pions at low transverse momentum for Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV. The azimuthal anisotropy difference between $\pi^+$ and $\pi^-$ will be shown as a function of net charge asymmetry and centrality. In addition, these results will be compared with model calculations.Speaker: Hongwei Ke (Central China Normal University)
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Charge azimuthal correlations at RHIC and LHC energies 2hWith a multi-phase transport model including initial charge separation and string melting, the charge azimuthal correlations for Au+Au collisions at center of mass energies 200, 39, 11.5, 7.7 GeV and Pb+Pb collisions at 2.76 TeV are investigated. Initial charge separations of about 10 % for 200 GeV, 5 % for 39 GeV, 0 % for 11.5 GeV appear to be necessary. This is consistent with decreasing Chiral Magnetic Effect as the incident energy decreases at RHIC. A reduced partonic interaction cross section is also needed for 11.5 GeV, indicating possible significant contributions from the hadronic stage. For Pb+Pb collisions at 2.76 TeV, 10% initial charge separation can produce similar behaviors as those at the top RHIC energy. We will also discuss how the same-charge correlation of <cos(1-2)> changes sign from negative at RHIC to positive at the LHC. Reference: [1] Guo-Liang Ma and Bin Zhang, Phys. Lett. B 700 (2011) 39–43, arXiv:1101.1701 [nucl-th].Speaker: Guo-Liang Ma (Shanghai INstitute of Applied Physics (SINAP), CAS)
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Charge dependent azimuthal correlations of K-Pi pairs at STAR 2hThree-particle correlations have been used to probe for local parity violation (LPV) in the quark-gluon plasma (QGP) formed during Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at RHIC [1]. Further expanding on this analysis, we present our results on looking at these correlations through pairing kaons and pions produced during the collision events (while fixing the third particle to be another pion). The idea behind looking at kaon-pion (K-Pi) correlations is that the two-body correlations between these distinct particles are weaker than those between pions with themselves. It may be that the tendency of two pions to be emitted at small angles to one another can be an important ingredient in a strong interaction background [2]. Hence, looking at K-Pi correlations may reduce potential effects from such backgrounds and possibly other parity-even effects that may contribute to the three-particle correlator. We present charge dependent azimuthal correlations between pions and kaons identified by using the Time-Of-Flight detector as a function of centrality, $\delta\eta$ and $\deltap_{T}$ between pairs in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Modifications depending on elliptic flow are also applied to the correlators as an additional measure to possibly reduce P-even background effects on the three-particle correlators. [1] B. I. Abelev et al., Phys. Rev. C81 (2010) 54908. [2] S. Schlichting and S. Pratt, arXiv:1005.5341v3 [nucl-th] (2010).Speaker: Charles Riley (Yale University)
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Charge dependent correlations relative to the fourth harmonic event plane and an estimate of the background effects in CME measurements 2hCharge dependent azimuthal correlations relative to the reaction plane measured by the STAR collaboration at RHIC and ALICE at the LHC are consistent with expectations from the strong local parity violation in QGP manifesting itself via the Chiral Magnetic Effect. The background to these measurements comes from interplay of strong anisotropic flow and correlations not related to CME. In this study, we present results on charge dependent correlations relative to the fourth harmonic event plane measured with the ALICE detector at the LHC in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV. These correlations, measured relative to the fourth harmonic event plane, are insensitive to the presence of CME, unlike the ones measured relative to the second harmonic event plane, but include possible backgrounds due to anisotropic flow thus providing an estimate of the background effects affecting the previous measurements.Speaker: Jocelyn Mlynarz (Wayne State University (US))
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Charm contribution to final hadron yield at LHC 2hAlmost all charm in heavy ion collisions is produced in the hard 'first interaction' processes before partons thermalize into a drop of QGP. Charm survives the QGP evolution and as hadrons emerge in soft hadronization processes, practically every charm or anticharm quark turns into a charmed hadron, small fraction of the charm yield enters multi-charmed hadrons and charmonium states. We assume that in the hadronization process the single charmed hadrons production is governed by the available phase space and their yield is normalized by the total single charm hadron yield. By allowing for charm hadron to charm hadron decay cascades, we establish total fraction of single charm hadrons found in their ground states. We show that the yields of charmed mesons can help to determine the charm hadronization temperature. We further cascade single charmed hadrons into non-charmed hadrons and show that at LHC these cascade products add significant fraction to certain strange hadron yields.We discuss particularly interesting examples such as phi (bar s s) and Xi(ssq). This shows that one cannot study charm and hadron production at LHC omitting the charm conversion into soft hadrons.Speaker: Michal Petran (Czech Technical University (CZ))
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Charm production in the early phase and the charm baryon-to-meson ratios at LHC energies 2hThe charm quark production will be reasonably large at LHC energies, both in p+p and Pb+Pb collisions. In heavy ion collisions even quark coalescence channels will strongly influence the charmed baryon and meson production. Furthermore, the formation of an intense coherent gluon field in Pb+Pb collisions results in additional heavy quark-antiquark pairs. Thus the primary charm quark momentum distribution will be modified, as well as the final state hadron distributions and the baryon-to-meson ratios in different momentum windows. We performed calculations with time dependent strong color fields and studied the charm quark-antiquark pair production and charmed hadron production in the intermediate- and high-pT windows at LHC energies. The obtained numerical results are presented and discussed. P. Levai, V.V. Skokov: Nonperturbative enhancement of heavy quark-pair production in strong SU(2) color field Phys. Rev. D82 (2010) 074014. P. Levai, D. Berenyi, A. Pasztor, V.V. Skokov: Anomalous baryon production and its interplay with jet energy loss at RHIC and LHC energies J. Phys. G38 (2011) 124155.Speaker: Peter Levai (Hungarian Academy of Sciences (HU))
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chi_c measurement in PHENIX: the present and the future. 2hMeasurement of different quarkonia states is a well known tool for study of hot and dense matter produced in heavy ion collisions. The PHENIX experiment at RHIC have successfully measured chi_c production in p+p and d+Au collisions at 200 GeV. The chi_c decays were reconstructed through their decays to J/Psi+gamma. Results from the 2006 p+p and 2008 d+Au datasets at 200GeV will be presented. The accuracy and pT reach of these measurements potentially can be improved if one uses conversions of soft photons from chi_c decays to e+e- pairs. These pairs can be then detected by the VTX detector recently installed in PHENIX. We present a simulation study of such measurement, and comparison to existing measurements.Speaker: Dr Alexandre Lebedev (Iowa State University)
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Chiral phase transition in a confining cold dense matter 2hThe question of the existence of a confining matter with restored chiral symmetry at low temperatures and large density has been studied within the confining and chirally symmetric model, assuming a rigid quark Fermi surface. However, in the confining matter near the Fermi surface quarks group into color-singlet baryons. Due to the interaction between quarks the quark Fermi surface gets diffused. Here we show that such diffusion does not destroy a possible existence of a confining but chirally symmetric matter.Speaker: Mr Vasily Sazonov (University of Graz)
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Chiral phase transition in a dynamical linear sigma model. 2hOne of today's main goals in high energy physics is the exploration of the phase diagram of nuclear matter. On the theoretical side, much effort has been put into the investigation of quantum chromodynamics (QCD), its phase diagramm and symmetries. An important property of the QCD Lagrangian is its approximate chiral symmetry in the light-quark sector. At low temperatures and density this approximate symmetry is also spontaneously broken, while at higher temperatures and/or densities a chiral-symmetry restoring phase transition is expected. Collider experiments at LHC (CERN) probe the phase diagramm at high energy densities and low chemical and baryon chemical potentials, where the chiral phase transition is expected to be a cross over. Future experiments at FAIR (GSI) probe the region with high chemical potential, where a lower-order phase transition is expected. We use a dynamical 3+1D linear sigma model with constituent quarks to examine the evolution of equilibrium and non-equilibrium scenarios. In a first attempt we employ a mean-field ansatz which reproduces the thermodynamical properties of the linear sigma model. To investigate fluctuating observables like the quark- and baryon-density at and near the phase transition, the model is extended with scattering processes between the quark quasi-particles and the chiral fields. For further improvments, we plan to include an effective Polyakov-loop to model effects of the confienment.Speaker: Christian Wesp (Goethe Universität Frankfurt)
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Chiral symmetry breaking in QCD and related theories 2hFor about a decade it is known that topological fluctuations -- instantons -- are modified by the nonzero Polyakov line VEV and split into Nc dyons. By now there is extensive lattice literature confirming this fact and explaining certain observations by properties of such dyons, mostly at T=(1-2)Tc. This talk report the first direct simulations of the statistical mechanics of the ``dyonic vacuum", using one-loop partition function. We found that chiral symmetry breaking and Dirac eigenvalues spectra are strongly affected by the LLbar dyon clustering. Among many consequences explaining lattice data is the dependence on the chiral transition on the number of fermion species Nf and the fermionic periodicity condition.Speaker: Edward Shuryak (stony brook university)
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Clustering of Color Sources and the Temperature Dependence of Shear Viscosity of the QGP in Central A-A Collisions at RHIC and LHC Energies 2hThe shear to viscosity ratios ($\eta/s$) are obtained for the QGP in the context of the Color String Percolation Model (CSPM) using data produced in Au-Au collisions at $\sqrt{s_{NN}}$ = 200 A GeV at RHIC and Pb-Pb at $\sqrt{s_{NN}}$ = 2.76 TeV at LHC \cite{per}. The experimental transverse momentum spectrum is used to measure the percolation density parameter $\xi$ in Au-Au collisions (STAR)\cite{eos}. The relativistic kinetic theory relation for $\eta/s$ is evaluated using CSPM values for the temperature and the mean free path of the QGP constituents \cite{gul1}. For Pb-Pb at $\sqrt{s_{NN}}$ = 2.76 TeV, $\xi$ values are obtained from the extrapolation at RHIC energy. The value of $\eta/s$ is 0.204$\pm$ 0.020 and 0.262$\pm$0.026 at the initial temperatures of 193.6 MeV (RHIC) and 262.2 MeV (LHC), respectively. These values are 2.3 and 3.2 times the AdS/CFT conjectured lower bound $1/4\pi$ but are consistent with the theoretical estimates of strongly coupled QGP.Speaker: Dr brijesh srivastava (Purdue University)
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Cold nuclear matter effects on $\Upsilon(1S+2S+3S)$ production 2h$\Upsilon(1S+2S+3S)$ are measured in $d$ + Au and $p$ + $p$ collisions at $\sqrt{s_{NN}} $= 200 GeV by the PHENIX experiment in the di-muon decay channel at 1.2 < |y| < 2.2. Compared to the $J/\psi$, the $Upsilon$'s heavier mass makes it possible to study the nuclear effects on the gluon distribution in different kinematic regions than those probed by the $J/\psi$. The measured results are compared to a nuclear shadowing model, EPS09 combined with a final state absorption cross section, $\sigma_{br}$, and contrasted with the PHENIX $J/psi$ results. We also will compare to lower energy $p$ + A results. Conclusive findings on $\sigma_{br}$ are difficult to obtain due to the large experimental uncertainties. However the degree of suppression is found to agree within uncertainties with the lower energy measurement as well as the $J/\psi$. In this poster, the details of the analysis procedure will be shown.Speaker: Kwangbok Lee (Losalamos National Laboratory)
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Cold quark matter in astrophysics of compact stars 2hI discuss the structure and composition of massive (two solar-mass) neutron stars containing deconfined quark matter in color superconducting states. Stable configurations featuring such matter are obtained if the equation of state of hadronic matter is stiff above the saturation density, the transition to quark matter takes place at a few times the nuclear saturation density, and the repulsive vector interactions in quark matter are substantial. I also discuss our recent progress in understanding the cooling of massive compact stars with color superconducting quark cores.Speaker: Dr Armen Sedrakian (Frankfurt University)
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Collective flow in relativistic heavy ion collisions 2hHeavy-ion collisions at relativistic energies ofer an unique opportunity to probe highly excited dense nuclear matter with properties very diferent from that of a hadron gas or ordinary nuclear matter in the laboratory. An interesting phenomenon at the kinetic freeze-out stage of the system evolution is the collective transverse expansion as it is entirely generated during the collision and therefore reflect the collision dynamics. Experimental data collected at RHIC have shown that the system produced in Au-Au collisions is thermalized and undergoes a strong collective expansion, that could be characterized by the Hubble law. The measurable observables that can provide information about thermalization and collective flow are the transverse momentum spectra of produced particles. The expansion rate at “thermal freeze-out” provides the nuclear collision analogue of the Hubble constant for the Big Bang, while the corresponding freeze-out temperature parallels the temperature of the cosmic microwave background at the point of photon decoupling. In this work we will make an estimate of a Hubble parameter for relativistic nuclear collisions similar to cosmological Hubble constant, based on temporal connections between the evolution of nuclear matter produced in a relativistic heavy ion collision and the Universe evolution after the Big Bang. We will present experimental data obtained in Au-Au collisions at RHIC energies and will compare with the same parameters obtained from simulated data at future CBM-FAIR energies. We will investigate the freeze-out process in heavy ion collisions at CBM-FAIR energies and we will present a study of blast-wave fits performed to the transverse momentum spectra obtained from simulated heavy ion collisions using the most important simulation codes from this field. In addition, comparisons with results from Au-Au collisions at RHIC energies will be presented to provide more detailed insight into the properties of the space-time evolution such as collective dynamics of the dense matter. We will compare the freeze-out kinetic parameters obtained from experimental data at RHIC energies with the same parameters obtained from simulated data at future CBM-FAIR energies using the most important simulation codes from this field.Speaker: Prof. Alexandru Jipa (Faculty of Physics, University of Bucharest)
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Collective Flow of Charged Hadrons in Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV at RHIC PHENIX 2hThe collective flow of charged hadrons emitted in heavy ion collisions can be characterized using the Fourier coefficient $v_2$ (elliptic flow), as well as with the higher order coefficients, $v_3$, $v_4$, etc, which result primarily from fluctuations in the initial conditions of the colliding nuclei.The latter is of paramount importance since it can provide insight on the hydrodynamic behavior of the medium, as well as constraints for reliable extraction of transport coefficients. For example, $v_3$ has been critical in discriminating between different models and the application of viscocity. In recent measurements, PHENIX has extracted $v_{2,3,4}$ coefficients for charged hadrons via two independent methods. The first correlates the azimuthal distribution of particles at mid-rapidity in the central arm of PHENIX with event planes determined by the detectors widely spaced in pseudorapidity to avoid non-flow effects. The second method is a two particle correlation between a charge weighted azimuthal angle in the Beam Beam Counters and the azimuthal angle of a track in the central arms of the PHENIX detector. Again, the pseudorapidity gap is present to avoid non-flow effects. This method has the added benefit of not requiring that the reaction plane angle be determined. These coefficients, measured as a function of the number of particpating nucleons, centrality, and $p_T$ for charged hadrons, will be presented and compared to earlier measurements for Au+Au collisions at the same energy so as to see the effect of system size.Speaker: Damian Reynolds (S)
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Collision energy dependence of high transverse momentum $R_{CP}$ of charged hadrons in STAR 2hThe observed suppression of high transverse momentum ($p_{T}$) hadrons in central Au+Au collisions at $\sqrt{s_{NN}}$ = 200GeV, expressed via the nuclear modification factor $R_{AA}$ ($R_{CP}$), is a clear indication of partonic energy loss due to the strongly-coupled medium created in heavy-ion collisions. That result is supported by high-$p_{T}$ triggered azimuthal di-hadron correlations which compare the measured correlated yield of recoil jets in heavy-ion collisions to p+p or peripheral collision reference measurements. The collision energy dependence of jet quenching measurements can be used to put further constraints on theoretical descriptions of partonic energy loss. We will present measurements of charged hadron $R_{CP}$ over a wide range of collision energies ranging from 7.7-200 GeV. In addition, we will present the analysis status of triggered di-hadron correlations at lower RHIC energies.Speaker: Stephen Horvat (Y)
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Constraining properties of the deconfined state of matter with CHIMERA 2hConstraining properties of the strongly interacting state of matter produced in relativistic heavy ion collisions at RHIC and LHC, such as eta/s and T_{init} is one of the biggest priorities in the field of heavy ion physics. For this purpose, we have developed CHIMERA, a framework for performing global statistical evaluation of multiple QGP signatures by comparing key soft observables (spectra, HBT and elliptic flow) measured at LHC and RHIC to the results from our multi-stage hydrodynamics/hadron cascade model of heavy ion collision. The unique feature of CHIMERA is that both statistical and systematic uncertainties are used in the evaluation procedure, and these uncertainties are fully propagated in the determination of the temperature and viscosity to entropy ratio. The CHIMERA model incorporates different initial state conditions, pre-equilibrium flow, the UVH2+1 viscous hydro model, Cooper-Frye freezeout, and the UrQMD hadronic cascade model. For hydrodynamical evolution, several different equations of state (EoS) , including those derived from the hadron resonance gas model and lattice QCD, are used to test the sensitivity of the observables to a particular choice of EoS. For a particular selection of initial conditions and pre-equilibrium flow we consider T_{init}-eta/s grid. For each grid point and a particular observable we evaluate the extent of agreement between the model and experimental data by calculating chi-squared values. The latest CHIMERA results of comparing LHC data to the results from our heavy ion collision model optimized for LHC energies will be presented.Speaker: Dr Irakli Garishvili (Lawrence Livermore National Laboratory)
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Constraining the Nuclear Equation of State by Neutron-Star Observables 2hRecently, the mass of the pulsar PSR J1614-2230 has been measured at a one-percent accuracy to be roughly two solar masses. This, in addition to the statistical analysis of neutron-star radii by Steiner, Lattimer, and Brown lead to tight constraints for the equation of state of dense baryonic matter inside the neutron star. We combine a realistic phenomenological equation of state at low densities with equations of state around nuclear densities derived both from chiral effective field theories, on one hand, and from the Polyakov-loop-extended Nambu--Jona-Lasinio model, on the other. Our analysis based on the Tolman-Oppenheimer-Volkoff equation strongly supports an equation of state of ordinary nuclear matter. This means, that there is no need to include exotic matter in order to stabilize a two-solar mass neutron star. Furthermore, with these constraints we draw conclusions for the QCD phase diagram.Speaker: Dr Thomas Hell (Technische Universität München)
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Construction of LMRPC modules for STAR-MTD 2hData taken over the last several years have demonstrated that the Relative Heavy Ion Collider (RHIC) has created dense and rapidly thermalizing matter. The next objective at RHIC is to study properties of this partonic matter in detail in terms of color degrees of freedom and the equation of state. The precise measurement of transverse momentum distributions of quarkonia at different centralities, collision systems, and energies will serve as a thermometer of QGP. A large-area and cost-effective Muon Telescope Detector (MTD) at mid-rapidity for the STAR was proposed. The MTD will be constructed with LMRPC instead of small pad read-out MRPC. With this design the number of electronic channels can be reduced effectively and the hit position along the strip can be obtained by the time differences of two ends of the strips. A prototype of Long-strip Multi-gap Resistive Plate Chamber (LMRPC) for STAR-MTD has been developed. This 5-gap prototype has an active area of 52x87 cm2 and the signals are read out from 12 strips, which are 3.8cm wide and 87cm long. The 5-gap STAR-MTD LMRPC module has a efficiency up to 98% and time resolution is in the order of 95 ps. The noise level of such modules is quite low. A special machine was developed to make the colloidal graphite electrodes. Using the time difference of the two PMT signals of each of the two long scintillators, a selection of perpendicular cosmic-ray particles is done to get a better time resolution evaluation. 22 LMRPC modules we have been built all passed QC and they have very good performance. The whole MTD consists of 117 LMRPCs and 60 modules will be produced in Tsinghua university. In this paper, the performance of the prototype, cosmic test facility and production status are described.Speaker: Yi Wang (Department of Engineering Physics, Tsinghua University)
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Conventional effects in higher cumulant ratios of conserved charges in relativistic heavy ion collisions 2hHigher cumulant ratios of conserved charges are suggested to be sensitive probe of QCD critical end point [1] in relativistic heavy ion collisions. Their behaviors at current relativistic heavy ion collisions are highly interested and studied intensively [2,3]. Before we draw the critical-like fluctuations from the measured higher cumulants, it is necessary to know what the contributions of conventional effects are. In the present work, we firstly derive the Poisson-like statistical fluctuations of net-proton number [4], and net-electric charge. It shows that net-proton kurtosis at top incident energy of RHIC [3] is dominated by Poisson-liked statistical fluctuations [4]. So dynamical higher moments, subtracting the statistical parts, are suggested. Secondly, the influences of the centrality, the efficiency of the detector, and the cuts of transverse momentum (pT) and rapidity in higher cumulant ratios of net-proton are systematically studied by using the sample of Au + Au collisions at 39GeV generated by APMT default model. It is found: (1) Both dynamical and directly measured cumulant ratios are sensitive to the definitions of centrality. (2) Dynamical cumulant ratios are little efficiency dependent. (3) Both dynamical and directly measured cumulant ratios are the cuts of phase-space dependent. References: [1] Volker Koch, arXiv:0810.2520. M.A. Stephanov, Phys. Rev. Lett. 102, 032301 (2009); Masayuki Asakawa et al., PRL 103, 262301 (2009); M.A. Stephanov,Phys. Rev. Lett 107, 052301(2011); [2] A.M. Halasz, A.D. Jackson, R.E. Shrock, M.A. Stephanov and J.J.M. Verbaarschot, Phys. Rev. D 58, 096007(1998); S.Gupta et al., Science 332, 6037(2011). [3] M.M.Aggarwal et al., (STAR Coll.), Phys.Rev.Lett. 105, 022302(2010). Talks at the Workshop On Fluctuations, Correlations and RHIC Low Energy Runs, http://www.bnl.gov/fcrworkshop/, and the 7th International Workshop on Critical Point and Onset of Deconfinement, http://conf.ccnu.edu.cn/~cpod2011/. [4] Lizhu Chen et al., J.Phys.G:Nucl.Part.Phys. 38, 115004(2011).Speaker: Prof. Yuanfang Wu (Institute of Particle Physics, CCNU, wuhan China)
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Critical fluctuations of the higher moments of order parameter and energy from 3D-Ising, O(2) and O(4) models 2hHigher moments of net-baryon are suggested to be sensitive probe of QCD critical end point [1] in relativistic heavy ion collisions. Their critical fluctuations are highly interesting and instructive for the exploration of QCD phase diagram from both theoretical and experimental sides. According to the universality of critical behavior, the QCD critical end point, and the chiral phase transition in two-flavor QCD are argued to be the same universality class of 3 dimensional Ising model [2], and O(2), or O(4) model[3], respectively. The generic structures of net-baryon fluctuations at QCD critical end point and chiral phase transition in the chiral limit with vanishing baryon chemical potential can be discussed by the order-parameter fluctuations in Ising model and the energy fluctuations in O(2), or O(4) model [4,5]. So in the present work, the higher moments of order parameter and energy from 3D-Ising, O(2) and O(4) models near the critical temperature at finite size are systematically studied, and compared with those obtained from effective models, and Lattice QCD calculations. It is found that the generic structures of order-parameter fluctuations in 3D-Ising, O(2) and O(4) models are similar. So do energy fluctuations. On the other hand, the singular structures of order parameter fluctuations appear at lower moments, e.g., the oscillation structures of 4th moment of order parameter, which may reflect the generic structure of 4th order moment of baryon number in the vicinity of critical end point, are similar to the 3rd moments of energy, which corresponding to the 6th moment of net-baryon number at chiral phase transition in the chiral limit with vanishing baryon chemical potential. This means that even higher moments, such as 6th moments of net-baryon number, are necessary in probing the chiral phase transition temperature, the same as what suggested in ref. [5]. The generic singular structures of order-parameter fluctuations in 3D-Ising and energy fluctuations in O(2), or O(4) models are qualitatively consistent with corresponding estimations of Nambu-Jona-Lasinio [6], Linear Sigma model [7], Polyakov-Nambu-Jona-Lasinio [8], Polyakov Quark Meson models [9], and current lattice QCD calculations [10]. [1] M.A. Stephanov, Phys. Rev. Lett 102, 032301 (2009) [2] R.D. Pisarski and F. Wilczek, Phys. Rev. D 29, 338(1984); F. Wilczek, Int. J. Mod. Phys. A 7, 3911(1992), A.M. Halasz, A.D. Jackson, R.E. Shrock, M.A. Stephanov and J.J.M. Verbaarschot, Phys. Rev. D 58, 096007(1998); [3] R.D. Pisarski and F. Wilczek, Phys. Rev. D 29, 338(1984);F. Wilczek, Int. J. Mod. Phys. A 7, 3911(1992); K.Rajagopal and F. Wilczek, Nucl. Phys. B 399, 395(1993) [4] J. J. Rchr and N. D. Mcrmin, Phys. Rev. A 8, 472(1973); Nigel B Wilding, J. Phys.: Condens. Matter 9, 585(1997); Chiho Nonaka and Masayuki Asakawa, Phys. Rev. C 71, 044904 (2005) [5] B. Friman, F. Karsch, K. Redlich and V. Skokov, arXiv:1103.3511(2011) [6] Masayuki Asakawa, Shinji Ejiri, and Masakiyo Kitazawa, Rev. Lett 103, 262301(2009) [7] M.A. Stephanov, Phys. Rev. Lett 107, 052301(2011) [8] Wei-jie Fu, Yu-xin Liu and Yue-Liang Wu, phys. Rev. D 81, 014028 (2010) [9] V. Skokov et al., Phys. Rev. D 82, 034029 (2010) [10] M. Cheng et al., Phys. Rev. D 79, 074505 (2009)Speaker: Prof. Yuanfang Wu (Institute of Particle Physics, CCNU, Wuhan, China)
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Cross section, polarization and multiplicity dependence of J/psi production in pp collisions at the LHC 2hThe measurement of J/psi production in proton-proton collisions at the LHC energy regime allows to test QCD calculations. In addition, it provides the necessary reference for the ALICE Pb-Pb program. ALICE collected proton-proton collisions at sqrt{s} = 7 and 2.76 TeV in 2010 and 2011. In this talk, we present the latest results on J/psi production in proton-proton collisions, measured by ALICE at both mid and forward rapidity via its leptonic decay channels. These results include the differential production cross section, the first LHC result on J/psi polarization, the charged particle multiplicity dependence of J/psi production and a measurement of non-prompt J/psi resulting from B-hadron decays at central rapidity down to very low p_t. Comparisons with different theoretical models will be discussed.Speaker: Fiorella Fionda (Universita e INFN (IT))
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D mesons $v_{2}$ measurement with Q-cumulants and Scalar Product methods in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV with the ALICE experiment 2hThe ALICE experiment at the Large Hadron Collider (LHC) has been designed in order to characterize the quark gluon plasma (QGP) in high-energy heavy-ion collisions. D mesons are powerful probes of the medium since the charm quarks are produced at the early stage of the collision and experience its entire evolution. In particular, the anisotropy parameter $v_2$ of D mesons is sensitive to the degree of thermalization of charm quarks within the QGP medium. The performance of the Q-cumulants and Scalar Product methods used to measure the $v_2$ of D mesons at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV will be shown. In particular, results for $\rm{D^{0}}$ and $\rm{D^{*}}$ obtained in the $\rm{D^{0}} \rightarrow K \pi$ and $\rm{D^{*}} \rightarrow \rm{D^{0}} \pi$ decay channels will be reported.Speaker: Grazia Luparello (NIKHEF (NL))
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D*-hadron azimuthal correlations in pp collisions at $\sqrt{s} =7 TeV$ with ALICE 2hDue to their relatively high mass, heavy-flavour quarks, produced in high-energy heavy-ion collisions, are sensitive probes of the interaction dynamics inside the hot and dense QCD matter. Since heavy quarks are produced in pairs during the initial stage of the collision, before the formation of the QGP, the measurement of heavy-flavour hadron production provides profound information on the properties of the produced medium. A detailed understanding of the pair production mechanisms in proton-proton collisions is interesting both as a QCD test tool as well as a reference for future heavy-ion studies. This particular physical process can be investigated using the angular azimuthal correlation between open-charmed mesons and charged hadrons. This correlation exhibits characteristic near-side and away-side structures that are produced by the charged hadrons from the fragmentation and decay of the partner charmed meson. The azimuthal direction is expected to be sensitive to the heavy quark production mechanism and can be compared to the perturbative QCD calculations. D mesons are reconstructed in several hadronic channels in the ALICE experiment at the LHC. Using $D*^{\pm}$ mesons is advantageous because they can be selected with higher purity with respect to D0 and $D^{+}$. Correlating with kaons (identified $K^{\pm}$ or reconstructed $K0_{S}$) that are produced with high probability in charm decays, provides a reduction of the background in the correlation distribution. In this contribution results of this correlation analysis, performed using the minimum bias proton-proton collisions at $\sqrt{s} = 7 TeV$ collected by the ALICE experiment in 2010, will be presented.Speaker: Sandro Bjelogrlic (University of Utrecht (NL))
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Decomposition of flow and non flow in di-hardon correlations at RHIC 2hAngular di-hadron correlation studies in Au+Au collisions at 200 GeV have revealed a nearisde elongated structure in delta eta. This is often referred to as the ridge, and was found to extend to delta eta 9 units at the LHC. Using preliminary STAR data [3], we discuss methods to decompose 2D di-hadron correlations in Au+Au 200 GeV collisions on the nearside. Our analysis is performed as a function of centrality and pT. We propose a model that encompasses azimuthal flow up to 4 orders (v1, v2, v3, and v4). The remainder of the correlation function is modeled via an asymmetric 2d Gaussian, which we refer to as non-flow. We find our model describes the data very well. The extracted flow parameters are compared to model predictions [4,5]. We investigate possible scalings for the Gaussian remainder, and compare it's properties to a similar structure observed in p+p 200 GeV collisions. These findings will help us shed on the production mechanism of the remainder. Finally, we will provide an estimate of the ratio of non-flow to flow as a function of centrality and pT, which will aid a variety of other flow studies at these energies. [1] B. I. Abelev et al. (STAR Collaboration), Phys. Rev. C 80, 064912 (2009) [2] M. Daugherity (for the STAR Collaboration), J. Phys. G: Nucl. Part. Phys. 35 104090 (2008) [3] L. C. De Silva, for the STAR collaboration [4] B. Alver et al., Phys. Rev. C 81, 054905 (2010) [5] C. Gombeaud et al., Phys. Rev. C 81, 014901 (2010)Speaker: Chanaka De Silva (Wayne State University)
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Density fluctuations at the QCD phase transition 2hWe study the nonequilibrium dynamics of a quark fluid coupled to a sigma field and a Polyakov loop near the QCD phase boundary. As the system evolves through the first order transition line, baryon density fluctuations are enhanced in comparison with an evolution through the crossover or the critical point.Speaker: Christoph Herold
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Development of the Silicon Tracking System for the Compressed Baryonic Matter (CBM) Experiment at FAIR 2hThe Compressed Baryonic Matter (CBM) experiment will conduct a comprehensive research programme on nuclear matter at high net baryonic densities. The Silicon Tracking System (STS) is the central detector of the CBM experiment. Its task is the standalone trajectory reconstruction of the high multiplicities of charged particles originating from high-rate beam-target interactions. The detector system shall be operational from the start of the CBM physics program at SIS-100 in 2018, and later at SIS-300. The silicon microstrip detectors must be radiation hard and are red out by a fast self-triggering front-end electronics. A low-mass construction must be achieved avoiding the front-end electronics, the cooling and cabling infrastructure in the aperture. The layout of the STS, mechanical constraints and the expected radiation environment will be shown. Progress with the STS engineering design will be presented as well as results from in-beam tests of prototypes.Speaker: Dr Juergen Eschke (GSI Helmholtzzentrum)
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Development of W+Si-pad/micro-pad based Electromagnetic Calorimeter for the ALICE upgrade 2hThe W+Si electromagntic sampling calorimeter has been proposed as one of the upgrade plans for the LHC-ALICE experiment. The role of this calorimeter is to add capabilities to measure direct photons, pi0's and jets over full azimuth in a forward rapidity region (2.5<eta<4.5). The physics goal with the calorimeter is to understand the dynamics and properties of strongly interacting matter created by relativistic heavy-ion collisions and the initial state of the collisions such as high density color field realized at small Bjorken-x. The W+Si sampling calorimeter is a highly segmented silicon-tungsten calorimeter. At present, two possible designs are being considered. One consists of three or four longitudinal sampling electromagnetic segments, where one segment is composed of 5-7 layers of tungsten (~3.5mm thickness) and 1cm x 1cm Si-pad readout. Si-pad readout is for the energy measurement. The first segment contains 2-4 longitudinal layers of high resolution Si-micro-pad (1mm x 1mm) or Si-pixel (100um x 100um) detectors for the position measurements and two gamma separation. The other is composed of full layers of W+Si pixel with extreme fine granularity. For the Si pixel, MIMOSA chip, which has been developed as one of the Monolithic Active Pixel Sensors (MAPS), is utilized for the calorimeter purpose. Prototypes of the W+Si-pad based calorimeter, readout analog ASICs with large dynamic range and front end module have been developed and built in 2011. The beamtest was conducted at CERN-PS in November 2011. The overall performance obtained in this beamtest and understanding of the detector performance via simulation will be presented. In addition to the performance evaluation, recent development of the prototype such as ASIC development and Si-micro-pad will be reported.Speaker: Taku for the ALICE-FOCAL Collaboration Gunji (University of Tokyo (JP))
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Di-electron Measurements in $p+p$ collisions by PHENIX using the Hadron Blind Detector 2hDi-electrons are among the most promising probes for studying the early, hot and dense stages created in relativistic heavy-ion collisions. They are color neutral and so interact only electromagnetically, thus carrying to the detectors information about the conditions and properties of the medium at the time of their creation. The di-electrons are emitted over the the entire space-time evolution of the collision and their spectrum thus carries a wealth of information. PHENIX has measured a large, unexpected enhancement in $Au+Au$ collisions in the low mass region ( 0.2 - 0.8 GeV/c$^2$ ), with respect to the baseline cocktail scaled from $p+p$ collisions. However, this result suffers from a large systematic uncertainty due to the huge combinatorial background of uncorrelated pairs from partially reconstructed $\pi^0$ Dalitz decays and $\gamma$ conversions. To combat this challenge, PHENIX installed a hadron blind detector ( HBD ) for the 2009 and 2010 RHIC runs. Its purpose is to tag and reject the combinatorial background coming from these decays. A reliable analysis of the 2010 $Au+Au$ data hinges on a complete understanding of the HBD and its unique characteristics. The 2009 $p+p$ run serves as a crucial testing ground for understanding the systematics associated with this novel detector. The proof-of-principle obtained in the $p+p$ HBD analysis will be presented in this poster.Speaker: Deepali Sharma (S)
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Di-jet properties in pp at sqrt(s) = 7 TeV and Pb-Pb at sqrt(s_NN) = 2.76 by LHC-ALICE 2hA di-jet produced by a hard scattering of partons plays a vital role to characterize the properties of hot and dense QCD matter produced in Pb-Pb collisions at LHC. In particular, a di-jet is one of the key probes to look for a medium response due to a strong jet quenching effect, as reported by the CMS and ATLAS collaborations. In this analysis, we used the data collected by the ALICE collaboration, in pp collisions at sqrt(s) = 7 TeV and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. Charged and neutral leading jets have been used to study the momentum balance with the recoiling charged jet. The di-jet momentum balance (A_J) in pp at sqrt(s) = 7 TeV as a function of charged particle multiplicity has been measured and is compared with the PYTHIA simulation. We also report the status of an analysis of di-jet measurement in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV to search for a possible medium response by a propagation of high energy jet, which is sensitive to parton energy loss.Speaker: Tatsuya Chujo (University of Tsukuba (JP))
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Dielectron Production in Au+Au-Collisions at $\sqrt{s_{NN}}$ =39 \& 62.4 GeV at STAR 2hIn the years 2010/11, the Solenoidal Tracker At RHIC (STAR) conducted a Beam Energy Scan (BES) over a wide range of center-of-mass energies with the purpose of studying the properties of the Quark-Gluon-Plasma (QGP) as well as searching for the onset of deconfinement and the critical point of the QCD phase diagram. The installation of the Barrel Time-Of-Flight-Detector (TOF) has enabled STAR to identify electrons over a wide momentum range. Combined with its large acceptance, excellent PID, and a low material budget in the runs of 2010/11, STAR now provides unique capabilities for the study of dielectron production in heavy ion collisions. Due to their negligible strong interaction with the dense medium created at RHIC, leptons can escape the interaction region undistorted and thus, carry direct information about the space-time evolution of the fireball created in relativistic heavy-ion collisions. In the special case of dileptons, their invariant mass ($m_{ee}$) serves as an additional observable: For the BES energies, later dielectron creation times are accessible in the Low-Mass-Region (LMR, $m_{ee}<1.1 GeV/c^2$) where the in-medium vector meson properties and its implications on the dielectron yield can be measured. Earlier creation times, on the other hand, can be studied in the Intermediate-Mass-Region (IMR, $1.1<m_{ee}<3 GeV/c^2$) in which the continuum yield allows a direct measure of the effective QGP temperature. In this regard, the dependence of these observables on the collision energy is of special interest. These aspects, in particular, make dielectrons favorable as a clean penetration probe for the bulk. The poster will present dielectron invariant mass spectra from Au+Au collisions at $\sqrt{s_{NN}}$ of 39 \& 62.4 GeV and its comparisons to cocktail simulations of known hadron sources. In addition, the energy dependencies of low mass dielectron production, as well as the slope parameters of $p_T$ distributions from IMR dielectrons will be discussed.Speaker: Mr Patrick Huck (CCNU/LBNL)
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Dijet asymmetry A_J within a partonic Boltzmann transport model 2hRecent experimental data measured in \sqrt{s}=2.76 TeV Pb+Pb collisions by ATLAS and CMS showed a significant imbalance in the transverse momenta of the two reconstructed jets with the highest transverse momenta. This momentum imbalance is assumed to be caused by the different energy and momentum loss of the di-jets by scatterings within the created medium. To investigate this momentum loss we extended the transport model BAMPS which solves the full 3+1D Boltzmann equation for partons based on pQCD cross sections. One feature of BAMPS is the stochastic modeling of 2 -> 2 as well as 2 <-> 3 scattering processes. We show that the simulations of the momentum imbalance A_J of full reconstructed jets within BAMPS are in excellent agreement with the experimental data. Due to the available particle information in configuration as well as momentum space within such a transport model, it is possible to reproduce the entire evolution of the reconstructed jets within the medium and gain a deeper understanding of the emerging jet shapes. With this information we explain the momentum imbalance of di-jets by different in-medium path lengths and thus different energy and momentum loss at parton-level.Speaker: Mr Florian Senzel (Goethe-Universität Frankfurt)
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Dimuon measurements in ALICE: The Muon Forward Tracker Upgrade Project 2hThe ALICE experiment is dedicated to the study of the quark gluon plasma in heavy-ion collisions at the CERN LHC. The Muon Forward Tracker (MFT) is under consideration by the ALICE Experiment to be part of its programme of detectors upgrade to be installed during the LHC shutdown planned for 2018. The MFT is a silicon pixel detector added in the Muon Spectrometer acceptance ($2.5 < \eta < 4$) upstream of the hadron absorber. The MFT will allow a dramatic improvement of the measurements that are presently done with the Muon Spectrometer and, in addition, will give access to new measurements that are not possible with the present Muon Spectrometer set-up. The enhanced pointing accuracy gained by the muon tracks will significantly improve the mass resolution for the low mass resonances $\omega$ and $\phi$, as well as $-$ to a lesser extent $-$ for the $J/\psi$ and $\psi'$. The measurement of these resonances down to low $p_\mathrm{T}$ in heavy-ion collisions represents a unique feature at the LHC. The precise measurement of the offset for the muon tracks will also permit a model-independent identification of open charm ($c\tau \sim 150~\mu$m) and beauty ($c\tau \sim 500~\mu$m) production, including displaced vertices related to $J/\psi$ production from $b$. In addition, the MFT will help to reject a large fraction of muons coming from pion and kaon decays, improving the signal over background ratio for all the observables. In order to establish the physics performances achievable at the luminosities expected after 2018, realistic simulations of the MFT setup are being performed within the AliRoot framework. Detailed results will be shown on the physics performances, including background treatment and rejection, for the measurement of low mass neutral mesons and the $J/\psi$ and $\psi'$ resonances down to low $p_\mathrm{T}$, in central Pb--Pb collisions at $\sqrt{s_{NN}} = 5.5$~TeV. An overview of the main technological issues related to the MFT project will also be given.Speaker: Antonio Uras (Universite Claude Bernard-Lyon I (FR))
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Direct Photon - Hadron Pair Correlations Measurement in Au+Au Collision at PHENIX 2hThe direct photon - hadron pair correlations serve as an excellent probe of the hot and dense medium created in the heavy ion collision at RHIC. The unmodified photon is used as a reference for the modification of the jet energy by the medium. The low cross section of QCD Compton scattering that produces direct photon - quark pairs added with the enormous production of the background photons requires large amount of Au+Au events to allow a measurement with convincing statistical certainty. In 2010 (Run 10) PHENIX has collected 8.2 billion events of Au+Au collision with 200 GeV of center-of-mass energy per nucleon, a factor of 1.5 times larger than the same collision system collected in 2007 (Run 7). Improvement can also be achieved by event-by-event based methods that would reject large number of the background photons and thus increase the signal-to-background ratio. We will present a feasibility status of the event-by-event isolation cut application in Au+Au collisions and give a status report on the measurement of direct photon - hadron pair correlations.Speaker: Nowo Riveli (O)
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Direct Photon and Lepton Pair Production from Viscous quark-gluon plasma 2hWe have studied the effect of shear viscosity effects on direct photons as well as lepton pair production from Quark Gluon Plasma (QGP). The production rate for both these two thermodynamic signals gets modified due to: (i) changed space-time evolution of the viscous fluid and (ii) non-equilibrium correction to the equilibrium distribution function. The non-equilibrium correction grows with viscosity as well as transverse momentum. Viscous effects on photon production are strong [1]. The space-time evolution of QGP was obtained by solving Israel-Stewart’s second order hydrodynamics for $\sqrt_{NN}$=200 GeV Au+Au collisions. Effect of viscosity is to stiffen the dilepton spectra and reduce the elliptic flow [2]. Although, the rate of applicability is limited in the pT range due to non-equilibrium effects, the thermometric signals can limit the initial temperature and viscosity, the ratios of dileptons to photons it is expected, can be a fairly good measure of viscosity without the uncertainty of initial conditions. Shear viscosity per entropy, it seems, does not change appreciably going from RHIC to LHC. We intend to explore this puzzle. [1] A.K. Chaudhuri and Bikash Sinha, Phys. Rev. C 83, 03405 (2011) [2] A.K. Chaudhuri and Bikash Sinha, to be publishedSpeaker: Bikash Sinha (V)
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Direct photon capabilities of the proposed MPC-EX detector at PHENIX 2hThe proposed MPC-EX detector is a Si-W preshower extension to PHENIX's existing Muon Piston Calorimeter (MPC). The MPC-EX consists of eight layers of alternating W absorber and Si mini-pad sensors. Located at large rapidities, 3.1 < |$\eta$| < 3.8, the MPC-EX and MPC access low-x partons in the Au nucleus in d+Au collisions. With the addition of the MPC-EX, the neutral pion reconstruction range extends to energies > 80 GeV, a factor of four improvement over current capabilities. Not only will the MPC-EX strengthen PHENIX's existing forward $\pi^0$ and jet measurements, it also provides the necessary $\pi^0$ rejection to make a direct photon measurement feasible. With this $\pi^0$ rejection, direct photon yields at high $p_{T}$, $p_{T}$ > 3 GeV, can be statistically extracted using a double ratio method. The direct photon $R_{dAu}$ measured with the MPC-EX will quantify the level of gluon shadowing or saturation in the Au nucleus at low-x, x ~ 10^-3, with a projected systematic error band a factor of four smaller than EPS09’s current allowable range. Direct photons at forward rapidities are optimally sensitive to the gluon distribution because, unlike pions, direct photons are only produced by processes that are directly sensitive to the gluon distribution at leading order. A measurement of the forward direct photon $R_{dA}$ will cleanly access and greatly expand our understanding of the gluon nuclear parton distribution functions and provide important information about the initial state in heavy ion collisions.Speaker: Sarah Campbell (I)
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Direct Photon Measurements at PHENIX 2hDirect photons are a unique probe that allows studying the different stage of ultrarelativistic heavy-ion collisions. The direct photon yield is sensitive to different production mechanisms, which dominate the expected direct photon spectra at different transverse momenta. Their production is also influenced by modifications of the initial state in heavy nuclei. Such modifications can be studied in d+Au collisions, and their understanding is crucial for interpreting heavy-ion data. PHENIX has measured the spectra of direct photons in different collision systems and at different energies, over a broad range of transverse momentum. Photons were measured with different methods, using different subsystems, to extend the range of transverse momentum and to minimize the size of systematic uncertainties. In p+p collisions, PHENIX has also measured isolated direct photons, as well as the fraction of direct photons from jet fragmentation. In this poster, we will present the latest results on direct photon measurements, in heavy-ion collisions as well as in p+p and d+Au collisions, and compare the results with theoretical models.Speaker: Baldo Sahlmueller
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Directed flow at midrapidity at the LHC 2hWe present the first extraction of the recently-proposed rapidity-even directed flow observable v1, obtained from an analysis of published two-particle correlation data from the ALICE Collaboration. An accounting of the correlation due to the conservation of transverse momentum restores the factorization seen in all other Fourier harmonics and thus indicates that the remaining correlation gives a reliable measurement of directed flow. We also present results from the first viscous hydrodynamic calculation of directed flow, and show that it is less sensitive to viscosity than higher harmonics. This allows for a direct extraction of the dipole asymmetry of the initial state, providing a strict constraint on the non-equilibrium dynamics of the early-time system. (Reference: arXiv:1203.0931)Speaker: Ekaterina Retinskaya (IPhT Saclay)
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Directed flow measurement in Pb-Pb collisions with ALICE at the LHC 2hDirected flow, v1, is measured over a wide range of pseudo-rapidity, |eta|<5.1, in Pb-Pb collisions at 2.76 TeV with ALICE at the LHC. The results of v1 are reported as a function of the pseudo-rapidity and the transverse momentum for different collision centrality classes. Using the neutral spectator deflection at beam rapidity we investigate both the rapidity asymmetric v1 which is sensitive to the collision reaction plane, together with the rapidity symmetric v1 which is sensitive to the energy fluctuations in the initial geometry. Results are compared to RHIC measurements. Possible effects of the energy fluctuations in the longitudinal (along the collision axis) direction on the directed flow are discussed.Speaker: Gyulnara Eyyubova (University of Oslo (NO))
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Dissipative Hydrodynamic Evolution of the QGP at Finite Baryon Density 2hThe first results of the heavy ion program at LHC [1] suggest that the near-perfect fluidity discovered at RHIC is a universal property of the quark-gluon plasma (QGP) above and around the crossover temperature. The recent developments in hydrodynamic studies take account of the effects of shear and bulk viscosities as well as fluctuations for the quantitative understanding of the hot medium. On the other hand, net baryon number is neglected in most of the modern hydrodynamic analyses even though it is fully conserved at forward rapidity. Since the net baryon carries valuable information on the remnant of the colliding nuclei and thus on the magnitude of kinetic energy loss for the QGP production in the yet-unknown early thermalization stage, the next task for hydrodynamic analyses should be to incorporate finite baryon density. In this study, I develop a novel dissipative hydrodynamic model with finite net baryon density to investigate the net baryon rapidity distributions at RHIC and LHC [2]. Baryon dissipation is taken into account together with shear and bulk viscosities by a generalized second order theory [3]. The state-of-art lattice QCD equation of state and the color glass type initial conditions are employed. The results show that the net baryon is carried to forward rapidity during the hydrodynamic evolution, which implies that the experimentally observed transparency of the collision at RHIC [4] is effectively enhanced. This indicates that the kinetic energy loss for the production of the hot medium at the initial stage is larger, and then a part of the energy is transferred back to the net baryon components through the strong medium interaction. Furthermore, the net baryon distribution is found sensitive to baryon diffusion as well as to viscosities. This opens a possibility of constraining all the transport coefficients experimentally, including the ones at finite density such as baryon diffusion coefficient and thermo-diffusion cross coefficient. The results indicate that the dissipative hydrodynamic modeling would be important for extracting unique properties of the hot medium even in the high-energy collisions. References: [1] K. Aamodt et al. [ALICE Collaboration], Phys. Rev. Lett. 105, 252302 (2010). [2] A. Monnai, arXiv:submit/0457509 (temporary identifier, to appear on 23 Apr 2012). [3] A. Monnai and T. Hirano, Nucl. Phys A 847, 283 (2010). [4] I. G. Bearden et al. [BRAHMS Collaboration], Phys. Rev. Lett. 93, 102301 (2004).Speaker: Akihiko Monnai (The University of Tokyo)
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Dynamical freeze-out in event-by-event hydrodynamics 2hIn hydrodynamical modeling of the ultrarelativistic heavy-ion collisions the freeze-out is typically performed at a constant temperature. In this work we introduce a dynamical freeze-out criterion, which compares the hydrodynamical expansion rate with the pion scattering rate [1]. Previous studies [2] have shown that differences between constant temperature and dynamical freeze-out criteria are small in the transverse momentum spectra, but the effect on flow anisotropies has not yet been studied. Recently many calculations have been done using event-by-event hydrodynamics, in which case the expansion rate does not necessarily behave as nicely as in the case of smooth initial conditions. Thus it is interesting to check how the dynamical freeze-out changes hadron distributions with respect to the constant temperature freeze-out. In this contribution we present hadron spectra and elliptic and triangular flow calculated using (2+1)-dimensional ideal hydrodynamics, and show the differences between constant temperature and dynamical freeze-out criteria. First we discuss the systematics of the dynamical freeze-out, and for simplicity these calculations have been performed using smooth initial states. Finally dynamical freeze-out condition is applied to event-by-event calculations to evaluate $v_2$ and $v_3$. We find that the differences caused by different freeze-out criteria are small in all studied cases. [1] C. M. Hung and E. V. Shuryak, Phys. Rev. C 57, 1891 (1998). [2] K. J. Eskola, H. Niemi and P. V. Ruuskanen, Phys. Rev. C 77, 044907 (2008).Speaker: Pasi Huovinen (Johann Wolfgang Goethe-Universität)
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Dynamical higher cumulant ratios of net and total protons at STAR 2hHigher cumulants of baryon number are suggested to be good probe of Critical Point of QCD phase transition in relativistic heavy ion collisions [1]. However, since the number of produced protons is still small at RHIC, it is pointed out [2] that the statistical fluctuation is not negligible, and should be subtracted from directly measured cumulants. So the dynamical cumulant ratios are suggested. Moreover, it is addressed that the sign of the dynamical net proton kurtosis will change to be negative when the critical point is approached from the crossover side of the phase transition [3]. In this poster, we present the energy and centrality dependence of dynamical net and total proton kurtosis for Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV at RHIC. The sign of dynamical kurtosis of net proton is discussed and compared to those of total proton. The results are also compared with AMPT model calculations. References [1] M. A. Stephanov, Phys. Rev. Lett. 102, 032301 (2009); R. V. Gavai and S. Gupta, Phys. Lett. B 696 (2011) 459; C. Athanasiou, et al., Phys. Rev. D 82, 074008 (2010). [2] Lizhu Chen, et al., J. Phys. G: Nucl. Part. Phys. 38, 115004 (2011). [3] M. Stephanov, Phys. Rev. Lett. 107, 052301 (2011).Speaker: Mr Zhiming Li (Institute of Particle Physics, CCNU, Wuhan, China)
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Elastic scattering, total cross-section and charged particle pseudorapidity density in 7 TeV pp reactions measured by the TOTEM Experiment at the LHC 2hThe TOTEM experiment at LHC measured the differential cross-section of elastic p+p scattering at 7 TeV, with the help of Roman Pot detectors placed as close as seven times the transverse beam size from the outgoing beams [1]. Results indicate an initial exponential decrease of dsigma/dt, followed by a significant diffractive minimum at |t| = (0.53 +- 0.01(stat) +- 0.01(syst)) GeV**2. For large |t| values, the cross-section exhibits a power law behavior. By extrapolation of measured elastic p+p cross sections to |t| = 0, TOTEM obtained a total elastic scattering cross-section of 24.8 +- 0.2(stat) +- 1.2(syst)) mb [2]. Applying the optical theorem and using the luminosity measurement from CMS, a total proton-proton cross-section of (98.3 +- 0.2(stat) +- 2.8(syst)) mb was deduced. TOTEM also measured the charged particle pseudorapidity density dN/deta in p+p collisions at 7 TeV, in the pseudorapidity range 5.3 < |eta| < 6.4 [3]. This measurement extends the analogous measurements performed by the other LHC experiments to the so far unexplored forward eta range. References: [1] "Proton-proton elastic scattering at the LHC energy of sqrt(s)=7TeV" The TOTEM Collaboration (G. Antchev et al.), Europhys. Lett., 95 (2011) 41001 [2] "First measurement of the total proton-proton cross-section at the LHC energy of sqrt(s) = 7 TeV" The TOTEM Collaboration (G. Antchev et al.), Europhys. Lett., 96 (2011) 21002 [3] "Measurement of the forward charged particle pseudorapidity density in pp collisions at sqrt(s) = 7 TeV with the TOTEM experiment" The TOTEM Collaboration (G. Antchev et al.), CERN-PH-EP-2012-106Speaker: Mate Csanad (for the TOTEM Collaboration)
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Elastic scattering: The undersides of quarkonia propagation and collectivity in the QGP 2hOne of the most advocated probes of the quark gluon plasma (QGP) properties is the $J/\psi$ suppression. However, the comparison between experimental data and theoretical scenarios is still rather inconclusive, as several mechanisms might participate to explain the observed suppression (sequential suppression, dynamical or statistical recombination, formation time,...), not to mention the cold nuclear matter effects. In recent experimental studies at PHENIX and STAR, the $v_2$ of the $J/\Psi$'s has been measured. In conjunction with $R_{AA}$, this observable should improve our understanding of quarkonia production in the QGP and puts higher constrains on models aiming at describing the $J/\psi$ suppression. However, most of them neglect the possible diffusion of $Q\bar{Q}$ correlations ("pre $J/\psi$'s") in the QGP although it is generically an essential ingredient for the understanding of the $v_2$ of all particles. Motivated by SPS results of $v_2^{J/\psi}$ and recent RHIC and LHC results suggesting a strong thermalization of charm quarks in the medium, our approach is focused not only on the suppression phenomenon but also on the physical evolution of those correlations, including an original treatment of their diffusion in the QGP due to their Compton scattering with gluons and the implications of such a diffusion on $J/\psi$ energy loss and collectivity, studied in a hydrodynamic transport model. The general tendency of our results indeed shows that elastic processes may have a non-negligible influence on the quarkonia propagation in the QGP. In our contribution, we will discuss the theoretical framework we have developed to evaluate the elastic cross section of $J/\psi$'s (and more generally $\Q\bar{Q}$ correlations) by combining analytical calculations based on pQCD and results from lQCD. We will then address the quarkonia propagation under the influence of such collisions, treated in a Fokker-Planck approach, and will present results deduced from our transport code MC@SHQ. Those results will be compared to recent STAR and PHENIX experiments at RHIC and predictions of $v_2^{J/\psi}$ for LHC will be shown.Speaker: Hamza Berrehrah (Subatech)
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Elliptic azimuthal anisotropy of neutral pions in PbPb collisions at 2.76 TeV with CMS 2hThe first measurements of the elliptic azimuthal anisotropy of neutral pions, pi0s, produced in 2.76 TeV PbPb collisions will be presented. The results are based on data collected by the CMS experiment during the 2010 LHC running period. The amplitudes of the second Fourier component (v2) of the pi0 azimuthal distributions are extracted using an event-plane technique. The values of v2 are studied as a function of the neutral pion transverse momentum (pT) for different centrality classes in the kinematic range pT = 1.6 - 8 GeV/c, and |eta|<0.8. The CMS measurements of v2(pT) agree with previously reported pi0 azimuthal anisotropy results from 200 GeV AuAu collisions measured by the PHENIX experiment at RHIC, despite a factor of ~14 increase in the center-of-mass energy. A comparison of the CMS measurements of v2(pT) from pi0 mesons and inclusive charged particles reveals a systematic difference in the range of pT = 2.5 ~ 5 GeV/c, with the neutral pion anisotropies being weaker than those observed for inclusive charged particles. This difference indicates a particle-species dependence in the azimuthal anisotropy at the LHC.Speaker: Monika Sharma (Vanderbilt University (US))
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Elliptic flow of high transverse momentum electrons from heavy-flavour decays in Pb-Pb collisions at sqrt(s_NN)=2.76 TeV measured by ALICE 2hHeavy quarks, charm and bottom, are produced in early stages of heavy-ion collisions. Propagating through the created matter they serve as a probe of the dynamics of the strongly-interacting, hot and dense plasma of quarks and gluons (QGP). The transverse momentum dependence of the elliptic flow (v2) of heavy quarks is sensitive to the properties of the QGP. A non-zero v2 of low transverse momentum electrons from semi-leptonic decays of heavy flavours indicates a collective motion of the heavy quarks with respect to the bulk of the created matter. Whereas, the high transverse momentum v2 is sensitive to the path length dependence of heavy-quark energy loss within the QGP. We present measurements of heavy-flavour electron v2 in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV by the ALICE experiment at mid-rapidity. In 2011, the Electromagnetic Calorimeter (EMCal) provided a dedicated online trigger for measurements of high momentum electrons in Pb-Pb collisions. The electrons were identified in these triggered events using the Time Projection Chamber (TPC) and the Electromagnetic Calorimeter (EMCal). The heavy-flavour electron v2 will be shown as a function of the transverse momentum of the decay electrons.Speaker: Denise Aparecida Moreira De Godoy (Universidade de Sao Paulo (BR))
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Elliptic flow of strange and multi-strange hadrons in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV measured with ALICE 2hAnisotropic flow of identified particles provides important information about the properties of the matter created in a heavy-ion collisions.We report the elliptic flow of strange (K$^0_s$ $\Lambda$) and multi-strange ($\Xi$ $\Omega$) hadrons measured at mid rapidity (|eta|<0.8) in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. The results are compared to measurements at RHIC energies and available model calculations.Speaker: Carlos Perez Lara (Nikhef, Utrecht University)
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Energy dependence of fluctuations in p+p collisions at the CERN SPS 2hNA61/SHINE at the CERN SPS is a fixed-target experiment pursuing a rich physics program including measurements for heavy ion, neutrino and cosmic ray physics. The main goal of the ion program is to explore the most interesting region of the phase diagram of strongly interacting matter. Within the expected (T - mu_B) interval we plan to study the properties of the onset of deconfinement and to search for the signatures of the critical point. Such 2D scan will be performed by varying collision energy (13A-158A GeV) and system size (p+p, Be+Be, Ar+Ca, Xe+La). Thanks to its large acceptance and good particle identification NA61/SHINE is well suited for study of event-by-event fluctuations. In this contribution preliminary results on energy dependence of transverse momentum, azimuthal angle and chemical composition fluctuations in p+p interactions will be shown. The new data will be compared with the corresponding results of NA49 on central Pb+Pb collisions.Speaker: Maja Katarzyna Mackowiak-Pawlowska (Johann-Wolfgang-Goethe Univ. (DE))
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Energy dependence of identified hadron multiplicity fluctuations in Heavy Ion collisions at the CERN SPS 2hThe study of event-by-event (e-by-e) fluctuations of chemical (particle-type) composition in high-energy nucleus-nucleus collisions is a helpful tool to pin-down the properties of strongly interacting matter. Indeed, according to theoretical calculations, the QCD critical point may be signalled by a characteristic pattern in the measured fluctuations. On the other hand, an incomplete particle identification may grossly bias final experimental results. In this context a new method for e-by-e fluctuations of identified particles will be introduced. In particular, using this method, the energy dependence of multiplicity fluctuations of identified particles in central Pb+Pb collisions, measured by NA49, will be presented.Speaker: Dr Anar Rustamov (Frankfurt University)
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Enhanced Jet Quenching in Strongly Interacting Quark Gluon Plasma 2hWe investigate the possibility of enhanced jet quenching in the vicinity of the critical temperature similar to the scenario proposed by Liao and Shuryak [PRL 102, 202302(2009)]. We discuss the consequences of the fact that the "shells" of such enhanced, critical quenching grow thinner as a function of the center-of-mass energy sqrt(s) of the collision. A systematic scan of jet quenching as a function of sqrt(s) can put constraints on such critical enhancement scenarios. Lastly we check existing constraints by comparing results from a numerical calculation using critical enhancement against high transverse momentum data from RHIC and LHC.Speaker: Prof. Ricardo Rodriguez (Ave Maria University)
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Entropy production in classical Yang-Mills system from color-glass condensate initial condition with noise 2hPossible thermalization mechanism in heavy-ion collisions is explored in classical Yang-Mills(CYM) theory with the initial condition of color-glass condensate with noise varied. We calculate the Lyapunov exponents and show that even a tiny noise triggers instability of the system and then a chaotic behavior sets in as described by the positive Lyapunov exponents, or Kolmogorov-Sinai(K-S) entropy, which would take a saturate value after a characteristic time dependent on the ratio of strengths of the noise to the back ground coherent fields. Thus we see that the entropy production is achieved in CYM theory with a realistic initial condition of relativistic heavy-ion collisions.Speaker: Hideaki Iida (Kyoto University)
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Event anisotropy of electrons from charm and bottom quark decays in 200 GeV Au+Au collisions at RHIC-PHENIX 2hThe production of heavy quarks is a powerful tool for investigating the dense partonic medium created in high energy heavy ion collisions. Due to their large masses, heavy quarks are mainly produced at the initial stage of the collisions. Therefore the heavy quark probes is sensitive to the full time evolution of the heavy ion collision. The PHENIX experiment measured the strong flow (v_2) of electrons from heavy quark decays. This indicates that the heavy quarks interacts with the medium more than it had been expected. However these measurements could not distinguish between charm and bottom decays, measuring instead an admixture of the two. We installed the silicon vertex tracker (VTX) in year 2011 as a detector upgrade. The VTX was designed to provide a clear separation of the charm and bottom contributions by measuring electrons with the distance of the closest approach to the primary vertex. In this poster, the analysis method will be described in detail and the status of electron flow from separated charms and bottoms in Au+Au 200GeV collisions at RHIC-PHENIX will be presented and discussed.Speaker: Dr Takashi Hachiya (RIKEN)
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Event by event di-hadron correlations in Pb-Pb 2.76 TeV collisions from the ALICE experiment 2hThe large multiplicities at the LHC permit flow harmonics to be determined on an event by event basis in Pb+Pb collisions. We extract these harmonics from inclusive event by event di-hadron correlations, where the minimum track pT is larger than 0.15 GeV. Within a fine centrality bin, we find the correlation function varies substantially on an event by event basis, indicating large fluctuations in the initial conditions for a given impact parameter. Such large fluctuations lead to some events being highly triangular or highly elliptical, where the angular correlation function is completely dominated by the respective cos(2#delta#phi) and cos(3#delta#phi) terms. We will show the 2D inclusive correlation function for such events, and access the covariance between different harmonics. Finally, we will present first measurements of the full v2 distribution for various centralities, and report the higher moments. Implications for our understanding of the initial conditions will be discussed.Speaker: Anthony Robert Timmins (University of Houston (US))
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Event-by-event distribution of azimuthal asymmetries in ultrarelativistic heavy-ion collisions 2hNowadays, relativistic dissipative fluid dynamics is a common tool to describe the space-time evolution of the quark-gluon plasma (QGP) created in ultrarelativistic heavy-ion collisions. The validity of the fluid-dynamical approach is experimentally confirmed by the fact that initial-state anisotropies are directly converted into nonvanishing (event-averaged) Fourier coefficients $\langle v_n \rangle$ of the decomposition of the single-inclusive momentum distribution of hadrons with respect to the azimuthal angle. From the magnitude of the $\langle v_n \rangle$ one can obtain information about the size of dissipative corrections and thus infer the value of the viscous coefficients of the QGP. It has been realized that, for a proper comparison to experimental data and a reliable extraction of viscosity, fluid-dynamical calculations have to be performed on an event-by-event basis. Therefore, fluid dynamics should not only be able to predict the correct event-averaged $\langle v_n\rangle$, but also their distributions. In this paper, we investigate the event-by-event distribution of the initial-state eccentricities $\varepsilon_n$, and show how they correlate with the event-by-event distribution of the Fourier coefficients $v_n$. In order to generate the initial state, we use the Monte-Carlo Glauber model of Ref.\ [1]. For the fluid-dynamical evolution, we use the model of Refs.\ [2]. The final hadron spectra are calculated with the Cooper-Frye freeze-out procedure. We demonstrate that the event-by-event distributions of the $v_n$, and not only their average values, are promising observables to gain information about the initial state of the fluid-dynamical evolution and the transport properties of the hot and dense, strongly interacting matter created in heavy-ion collisions. [1] H.~Holopainen, H.~Niemi, and K.~J.~Eskola, Phys.\ Rev.\ {\bf C83}, 034901 (2011), [arXiv:1007.0368 [hep-ph]]. [2] H.~Niemi, G.~S.~Denicol, P.~Huovinen, E.~Molnar, and D.~H.~Rischke, Phys.\ Rev.\ Lett.\ {\bf 106}, 212302 (2011), [arXiv:1101.2442 [nucl-th]]; H.~Niemi, G.~S.~Denicol, P.~Huovinen, E.~Molnar and D.~H.~Rischke, arXiv:1203.2452 [nucl-th].Speaker: Dr Harri Niemi (University of Jyväskylä, Department of Physics)
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Event-by-Event Fluctuations in Initial Conditions in Relativistic Hydrodynamic Model 2hTo investigate the physics of the strongly interacting system of quarks and gluons under extreme conditions, heavy-ion collision experiments are performed at Large Hadron Collider (LHC) and Relativistic Heavy Ion Collider (RHIC). One of the major discoveries is that elliptic flow v_2 was comparable with an ideal hydrodynamic prediction and, as a result, that a new paradigm of strongly coupled quark-gluon plasma (QGP) at temperature of a few hundreds MeV was established. Recently, the higher harmonics v_n (n > 2) are observed at RHIC and LHC and attract a lot of theoretical and experimental interests. Initial condition with fluctuation from initial nucleon distribution in colliding nuclei is attributed to one of the major origins of the higher harmonics. To understand detailed mechanism of how the higher harmonics develop, we construct an integrated dynamical framework based on relativistic hydrodynamics [1] and perform massive numerical simulations (10^5 minimum bias events) on an event-by-event basis [2]. In this framework, the Monte-Carlo versions of factorized Kharzeev-Levin-Nardi (fKLN) model (MC-KLN) and Glauber model (MC-Glauber) are employed as the initialization models. After describing hydrodynamic evolution of the matter using fully (3+1) dimensional ideal hydrodynamics, we treat the subsequent dynamics of hadron gas using a hadron cascade model, JAM. Using the obtained momentum distribution of the final hadrons, we finally analyze the harmonics v_n in a way that experimental people perform the flow analysis such as event plane method, multi-particle cumulant method. We compare these results with the conventional theoretically-obtained harmonics with respect to reaction plane or participant plane to investigate the systematic uncertainty in the conventional theoretical results. We found that v_n obtained in this way depends on the flow analysis model, which means the importance of consistent comparison between theoretical results with experimental data. We also calculate v_n as a function of centrality using the MC-KLN and MC-Glauber initialization and found differences of v_2, v_4 and v_5 between these two models. This indicates the simultaneous analysis of several harmonics would discriminate between the initialization models. [1] T. Hirano and Y. Nara, ``Dynamical modeling of high energy heavy ion collisions,'' arXiv:1203.4418 [nucl-th]. [2] T. Hirano, P. Huovinen, K. Murase and Y. Nara, in preparation.Speaker: Koichi Murase (The University of Tokyo)
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Event-by-event generation of electromagnetic fields in heavy-ion collisions 2hWe compute the electromagnetic fields generated in heavy-ion collisions by using the HIJING model. Although after averaging over many events only the magnetic field perpendicular to the reaction plane is sizable, we find very strong electric and magnetic fields both parallel and perpendicular to the reaction plane on the event-by-event basis. We study the time evolution and the spatial distribution of these fields. In particular, the electromagnetic response of the quark-gluon plasma can give nontrivial evolution of the electromagnetic fields.Speaker: Xu-Guang Huang (Institute for Theoretical Physics)
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Event-by-event mean $p_{\rm T}$ fluctuations measured by the ALICE experiment at the LHC 2hResults on event-by-event fluctuations of the mean transverse momentum of charged particles measured by the ALICE experiment at the LHC are compared to different Monte Carlo approaches. For these studies pp collisions at $\sqrt{s}$~=~0.9, 2.76 and 7~TeV and Pb--Pb collisions at $\sqrt{s_{\rm NN}}$~=~2.76~TeV are used. The analysis is performed within $|\eta| < 0.8$ and $0.15 < p_{\rm T} < 2 $~GeV/c. The data shows only a small collision energy dependence and indicates a common scaling behaviour with event multiplicity from pp to semi-central Pb--Pb collisions. In central Pb--Pb collisions, the results deviate from this trend, exhibiting a significant reduction of the fluctuation strength. A systematic comparison of ALICE results in pp to PHOJET and different tunes of the PYTHIA6 and PYTHIA8 event generators is presented. The study indicates a sensitivity of the data to different mechanisms to model high-multiplicity pp events. A comparison of Pb--Pb results to HIJING and AMPT suggests a strong relation between transverse momentum fluctuations and collectivity in central events, and disfavors an independent superposition scenario.Speaker: Stefan Thomas Heckel (Johann-Wolfgang-Goethe Univ. (DE))
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Exclusive photoproduction of rho0 mesons in ultra-peripheral Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV 2hThe strong electromagnetic fields generated in the collision of Pb ions at the LHC allow photon-photon and photonuclear interactions to be studied in a kinematic regime unexplored so far. The exclusive photoproduction of vector mesons was studied with the ALICE detector in ultra-peripheral PbPb collisions, where the impact parameter is larger than the sum of the nuclear radii and hadronic interactions are strongly suppressed. A data sample corresponding to about 3.6 microb^-1 was collected during the 2010 LHC heavy-ion run at an energy sqrt(s_NN) = 2.76 TeV using triggers that select ultra-peripheral collisions. In this data sample, Rho0 photoproduction at mid-rapidity corresponds to a photon-nucleon center of mass energy of 45 GeV, about 4 times higher than in previous experiments. The cross section for exclusive rho0 production was measured, and the relative contributions to the invariant mass distribution from resonant and non-resonant processes was evaluated. The results are compared to calculations with different theoretical models.Speaker: Christoph Mayer (Polish Academy of Sciences (PL))
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Extruction of nontrivial correlation between chiral and deconfinement transitions from two-color QCD at imaginary chemical potential 2hWe investigate the nontrivial correlation between the chiral and deconfinement transition in the two-color QCD. To extract the information, the imaginary chemical potential is taken into account. At $\theta = \pi/2$ where $\theta$ is the imaginary chemical potential divided by the temperature, there is the exact nontrivial center symmetry which is the $Z_2$ symmetry and this symmetry can be spontaneously broken. This behavior is quite different form the three-color QCD because the nontrivial center symmetry is always broken by the quark degree of freedom in the three-color QCD. This means that we can investigate the nontrivial correlation between the chiral and deconfinement transitions in the two-color system clearly than that in the three-color system. Such nontrivial correlation is very important to construct the effective model of QCD and thus we can expect that several important model constraints are obtained from the two-color QCD analysis. In this study, we mainly pay attention to the behavior of the Roberge-Weiss (RW) endpoint which appears at $\theta=\pi/2$ in the tho-color system. We show that the RW endpoint is second-order if the nontrivial correlation is weak, but it turn into first-order when the nontrivial correlation is sufficiently strong.Speaker: Kouji Kashiwa (RIKEN BNL Research Center)
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Flow correlations to constrain the properties of the initial conditions 2hIn this work, we propose a new ow correlation observable that provide valuable information about the geometrical properties of the QGP at the thermalization time. An event-by-event analysis within a longitudinal tube initial condition model shows that emitted particles high pt higher than 1 GeV are extremely sensitive to the level of granularity present in the initial conditions. Therefore, we studied the eect of the width and the energy content of the tubes in the correlation of ow calculated in dierent pt cuts. On the other hand, we are able to extract the values of these parameters from the NEXSPheRIO model. Furthermore, we applied this analysis to STAR experimental data in order to constrain the properties of the QGP generated at AuAu RHIC collisions. The knowledge about the geometrical properties of the initial conditions provides an important step in phenomenologically relating the nal observ- ables obtained experimentally and theoretical QCD predictions.Speaker: Philipe Mota (Goethe Universität Frankfurt)
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Fluctuating Hydrodynamics Confronts the Rapidity Dependence of Transverse Momentum Fluctuations 2hInterest in the development of the theory of fluctuating hydrodynamics is growing [1]. Early efforts suggested that viscous diffusion broadens the rapidity dependence of transverse momentum correlations [2]. That work stimulated an experimental analysis by STAR [3]. We attack this new data along two fronts. First, we compute STAR’s fluctuation observable using the NeXSPheRIO code, which combines fluctuating initial conditions from a string fragmentation model with deterministic viscosity-free hydrodynamic evolution [4]. We find that NeXSPheRIO produces a longitudinal narrowing, in contrast to the data. Second, we study the hydrodynamic evolution using second order causal viscous hydrodynamics including Langevin noise. We obtain a deterministic evolution equation for the transverse momentum density correlation function. We use the latest theoretical equations of state and transport coefficients to compute STAR’s observable. The results are in excellent accord with the measured broadening. In addition, we predict features of the distribution that can distinguish 2nd and 1st order diffusion. J. Kapusta, B. Mueller, M. Stephanov, arXiv:1112.6405 [nucl-th]. S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97, 162302 (2006), arXiv:nucl-th/0606061. H. Agakishiev et al., STAR, Phys. Lett. B704, 467 (2011), arXiv:1106.4334 [nucl-th]. M. Sharma, C. Pruneau, S. Gavin, J. Takahashi, R. Derradi de Souza, T. Kodama, Phys. Rev. C84, 054915, (2011), arXiv:1107.3587 [nucl-th].Speaker: Sean Gavin (Wayne State University)
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FoCal - a high granularity electromagnetic calorimeter for forward direct photon measurements as an upgrade of ALICE 2hWe report on the new design of a forward electromagnetic calorimeter (FoCal) to be placed in the pseudorapidity region of $2.5 < \eta < 4.5$, which is under consideration as an upgrade of the ALICE experiment at the CERN-LHC. The physics goals of including the calorimeter in the forward direction are to study outstanding fundamental QCD problems at low Bjorken-x values, such as parton distributions in the nuclei, to test pQCD predictions, and to probe high temperature and high density matter in greater detail. As a very promising probe we intend to study direct photons and correlations involving photons, pions, and jets over a broad range rapidity in p-p, p-Pb and Pb-Pb collisions at the highest LHC energies. For these measurements, the detector needs to be capable of measuring photons of energies up to several 100 GeV and be able to discriminate them from neutral pions. This will require a detector of unprecedented granularity. The detector design consists of silicon sensor layers interleaved with layers of tungsten absorber. The use of both conventional silicon sensors and of monolithic pixels is investigated. We will discuss the detector requirements and design options and will present results of Monte-Carlo simulations and test measurements with detector prototypes.Speaker: Taku Gunji (University of Tokyo (JP))
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Formation and decay of hadronic resonances in hot and dense nuclear matter 2hOne of the fundamental objectives of experiments with ultra-relativistic heavy ions is the study of hadronic matter at high density and high temperature. In this investigation we study in particular the information which can be obtained by analyzing baryonic and mesonic resonances in both hadronic and leptonic decay channels. The decay products of these resonances carry information on the resonance properties at the space time point of their decay. We especially investigate the percentage of reconstructable resonances as a function of density for heavy ion collisions in the energy range between $E_{lab}$ = 30~AGeV and $\sqrt{s}$ = 200~AGeV, the energy domain between the future FAIR facility and the present RHIC collider. We will show the dependency of the reconstructability of resonances on baryon density, which unexpectedly increases with higher density. We will explain this phenomenon by analyzing the points of origin and the transverse momentum of the resonances. The differences between RHIC and FAIR energies will be explored. Additionally we study leptonic decay channels and argue that dileptons, contrary to the common thinking only offer a restricted view on the hot and dense phase of heavy ion collisions. Finally we will suggest measurements that might circumvent those problems.Speaker: Dr Sascha Vogel (Frankfurt Institute for Advanced Studies)
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Forward J/psi production in Au+Au and Cu+Au collisions at PHENIX 2hOne important theoretical model of heavy ion collisions expects that the collision zone can be divided into two distinct regions: the core and the corona. The corona region is a low density p+p or p+A like region which may be a more favorable for J/psi production as opposed to the hot, dense core. From a Glauber model, this region is found to be symmetric about the reaction plane in Au+Au collisions, but is distinctly asymmetric in Cu+Au collisions. In this poster, we will describe the expected geometrical asymmetry in terms of the Glauber model implementation and show our initial studies of forward J/psi production toward measuring the relative size of the corona as a function of system-size.Speaker: Dr Aneta Iordanova (University of California, Riverside)
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Fourth order corrections to the MV model, multiplicity distributions and KNO scaling 2hA scaling law for the multiplicity distribution in high-energy hadronic collisions has been proposed by Koba, Nielsen, and Olesen (KNO). Experiments at the LHC observed that multiplicities in the central region of proton-proton collisions follow a negative binomial distribution and that they do exhibit KNO scaling. The negative binomial distribution has been theoretically reproduced in the Color Glass Condensate (CGC) formalism with a Gaussian (McLerran-Venugopalan) action. We derive corrections to the MV model up to fourth order in the density of color charges (rho^4) and investigate their implication on the multiplicity distribution and on KNO scaling. We find that KNO scaling constrains the deviation of the small-x effective action from a Gaussian.Speaker: Elena Petreska (Graduate Center/Baruch College CUNY)
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From dileptons to chiral symmetry restoration: Sum rules and the axial-vector spectral function. 2hThe medium modifications of vector and axial-vector spectral functions are investigated using Weinberg and QCD sum rules in an attempt to establish chiral symmetry restoration. Such a study is essential for the interpretation of a pertinent signal from dilepton data in heavy-ion collisions. We start from vacuum spectral functions which include both ground- and excited-state resonances for both the vector and axial-vector channels, supplemented by an identical perturbative continuum. The vacuum spectral functions are constructed to agree with tau decay data and Weinberg sum rules. In the medium, the rho spectral function is taken from effective hadronic many-body theory which is consistent with available dilepton data. The in-medium properties of the rho' are constrained by satisfying the in-medium QCD sum rule. For the axial-vector channel, different ansaetze are chosen for the in-medium a1 (broadening, mass drop, two-level model), while the medium modification of the excited state is again constrained by the QCD sum rule. These different ansaetze are then tested for chiral symmetry restoration through the Weinberg sum rules.Speaker: Paul Hohler (Texas A&M University)
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Fully dynamic simulations of heavy ion collisions in a pQCD-based partonic transport model 2hWe present fully dynamic simulations of central and non-central heavy ion collisions at LHC and at RHIC energies within the perturbative QCD-based partonic transport model BAMPS (Boltzmann Approach to Multi-Parton Scatterings). We focus on the simultaneous investigation of bulk properties, such as elliptic flow, viscosity and thermalization, and of high-pT observables, such as jet quenching. The model incorporates binary interactions of gluons and quarks based on pQCD cross sections in small angle approximation as well as 2<->3 processes based on the Gunion-Bertsch matrix element. We discuss symmetry properties of the radiative Gunion-Bertsch matrix element and compare to the exact result by Berends et al. The implications on the interaction rates and the dynamics of the medium are explored. We investigate the thermalization and viscosity of the medium, the elliptic flow as well as the nuclear modification of high-pT particles in Au+Au collisions at RHIC energies and in Pb+Pb collisions at LHC energies.Speaker: Oliver Fochler (Goethe-Universität Frankfurt)
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Getteing primordial baryon number fluctuation from observed proton number fluctuation in relativistic heavy ion collisions 2hWe explore the relation between proton and nucleon numberfluctuations in the final state in relativistic heavy ion collisions. It is shown that the correlations between the isospins of nucleons in the final state are almost negligible over a wide range of collision energy. This leads to a factorization of the distribution function of the proton, neutron, and their antiparticles in the final state with binomial distribution functions. Using the factorization, we derive formulas to determine nucleon number cumulants, which are not direct experimental observables, from proton number fluctuations which are experimentally observable in event-by-event analyses. With a simple treatment for strange baryons, the nucleon number cumulants are further promoted to the baryon number ones. Experimental determination of the baryon number cumulants makes it possible to compare various theoretical stduies on them directly with experiments. Effects of nonzero isospin density on this formula are addressed quantitatively. It is shown that the effects are well suppressed over a wide energy range.Speaker: Prof. Masayuki Asakawa (Osaka University)
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Hadron-jet correlations measured in pp and Pb-Pb collisions in LHC-ALICE 2hHeavy-ion experiments at the highest beam energy in the world (Pb-Pb at sqrt(s_NN) = 2.76 TeV) have started in 2010 at the Large Hadron Collider (LHC) at CERN. At the LHC, jet production is more abundant than at RHIC. Jet measurements play a critical role not only for probing the hot and high energy density matter in heavy ion collisions through parton energy loss, but also to observe possible modifications of the hot and dense matter itself by the lost energy. Hadron-jet correlations allow us to maximize the pathlength of the parton through the medium by selecting trigger hadrons with high transverse momenta that are biased to coming from the surface of the QGP. In this poster, we report the current analysis status of the recoil jet yield with charged particle triggers in Pb-Pb collisions from 2011 at sqrt(s_NN) = 2.76 TeV. We will also compare these results with correlation from baseline pp measurements at the same collision energy.Speaker: Daisuke Watanabe (University of Tsukuba (JP))
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Hadronic Calorimetry in sPHENIX at RHIC Upgrade Project 2hThe RHIC physics programs will benefit from developments in hadronic calorimetry. Hadronic calorimetry serves to identify and characterize jets in p+p and A+A collisions and enables studies of the mechanisms of partonic energy dissipation in the medium at high densities and temperatures. The sPHENIX detector concept requires development of a hadronic calorimeter with fairly high sampling fraction. The structure under study is a geometrically pointing longitudinally segmented calorimeter built of flat variable thickness absorber plates and constant thickness scintillating tiles forming azimuthal segments with finned structure. We will demonstrate the feasibility of building such a uniform and hermetic hadronic calorimeter and discuss concepts for light collection and readout.Speaker: Dr Edouard Kistenev (Brookhaven National Laboratory)
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Hadronic calorimetry R&D for future PHENIX 2hThe PHENIX detector was designed and built at the Relativistic Heavy Ion Collider to explore matter created in collisions of heavy nuclei. PHENIX, as an infrastructure of technologically different systems, has been recording data since 2000. Research results by the PHENIX experiment have already made an impact on the broad field of experimental nuclear physics. Being in its second decade of research, PHENIX intends to expand its physics program; thus consideration of possible upgrades has recently started. Calorimetry detectors are expected to be part of the upgraded PHENIX in forward and central regions. We consider a sampling detector that uses plastic scintillator tiles for future PHENIX hadronic calorimeters. The R&D program has commenced and, as its first phase, a reconfigurable sampling scintillator prototype calorimeter is being fabricated. With its lateral active detection area of 35 cm x 35 cm, the calorimeter will be capable of taking data with electron and hadron beams. The fabricated prototype calorimeter will allow comprehensive test beam studies to research and optimize design and technical performance parameters of the possible future hadronic calorimeter. In addition, evaluated metrological limits and production costs will be used in the technical design of PHENIX upgrades.Speaker: Dmitri Kotchetkov (Ohio University (US))
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Hadronic effects on the X(3872) meson abundance in heavy ion collisions 2hWe study the absorption of hadronic molecules such as the X(3872) by pions and rho mesons during the hadronic stage of heavy ion collisions. We also investigate the possibilities of formation of hadronic molecules during different evolution stages of the hadronic phase. We show that the absorption cross section and its thermal average are strongly dependent on the structure and quantum number of X(3872). We thus suggest that studying the abundances of a set of exotic hadrons provide a chance to infer their structures as well as their production mechanisms in relativistic heavy ion collisions.Speaker: Sungtae Cho
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Hadronic Resonance States in an Effective Chiral Model 2hWith an effective hadronic chiral flavor SU(3) model we investigate properties of QCD matter for a wide range of temperatures and baryochemical potentials. With our model, including all hadronic resonances up to masses of 2.6 GeV, we show that the strengths of the resonance couplings to the attractive scalar and the repulsive vector fields have a major impact on the order and location of the chiral phase transition. Reasonable vector couplings, found by comparing model data to recent lattice QCD results, limit the phase transition to a smooth cross over and therefore rule out the possible existence of a critical end point. Furthermore, we study fluctuations of conserved charges at the phase transition and present related (strange) quark number fluctuations and their associated susceptibility coefficients both at zero baryochemical potential and when crossing the phase transition at different regions in the T-mu plane. We show that susceptibility ratios get significantly suppressed at non-vanishing baryochemical potentials.Speaker: Mr Philip Rau (Goethe University Frankfurt, Germany)
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Hadronization: does the chemical freeze-out curve meet the lattice QCD parton-hadron phase boundary ? 2hWe analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS energies, employing the hybrid version of the Ultrarelativistic Quantum Molecular Dynamics model, which describes the transition from a hydrodynamic stage to hadrons by the Cooper-Frye mechanism, and matches to a final hadron-resonance cascade. We fit the results both before and after the cascade stage using the Statistical Model, to assess the effect of the cascade phase. We observe an upward shift of the statistical model freeze-out curve over the entire range of SPS energies if we omit the significantly absorbed antibaryon species from the fit. The freeze-out curve shifts closer to the lattice parton-hadron phase transition line. The corresponding effects are studied at RHIC and LHC energies where the final state annihilation affects both the baryon, and antibaryon yields. reference: arXiv:1201.6349 to appear in Phys. Rev. CSpeakers: Francesco Becattini (Unversity of Florence), Mr Tim Schuster (Yale University (US))
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Harmonious Harmonics? After the common origin of correlations and flow. 2hWe show that initial state fluctuations in concert with later-stage hydrodynamic flow describes a range of observables including both even and odd flow harmonics, the ridge, and multiplicity, momentum and flow fluctuations [1]. This is the first comparison between multiplicity and transverse momentum fluctuations and flow fluctuations in the same framework. The simultaneous investigation of these observables allows us to study the interplay of correlations induced by collision geometry and common points of production. We employ a framework of initial state Glasma flux tubes followed by later stage hydrodynamic flow modeled in a blast wave. Our approach has the advantage that we can test our calculations over a broad range of collision systems and energies and provide useful benchmarks for more rigorous event-by-event hydrodynamic simulations. Our survey over these observables reveals a common energy and centrality dependence that we attribute to the production mechanism. Glasma calculations are consistent with this dependence [2,3]. [1] S. Gavin and G. Moschelli, in preperation [2] S. Gavin, L. McLerran, and G. Moschelli, Phys. Rev. C79, 051902 (2009), arXiv:0806.4718 [nucl-th] [3] S. Gavin and G. Moschelli, Phys.Rev. C85, 014905 (2012), arXiv:1107.3317 [nucl-th]Speaker: George Moschelli (Frankfurt Institute for Advanced Studies)
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HBT Measurements for charged pions in √s_{\text{}NN}=39, 62.4 and 200 GeV Au+Au collisions at RHIC-PHENIX 2hHBT measurements are sensitive to the expansion dynamics of the system and they can provide information on the size of the source in space and time at freeze-out (hadron decoupling). Previously, the size of the region of homogeneity has been shown to have an almost linear dependence with particle multiplicity at different beam collision energies. A question of interest is whether the same trend extends across the range in beam energies recently obtained for run-10 of RHIC. To address this question, results for HBT measurements for charged pion pairs at √s_{\text{}NN}=39, 62.4 and 200 GeV beam energies Au+Au collisions, obtained using the PHENIX detector, will be presented. These results will be compared to previous findings at lower collision energies and varying collision systems. The results will also be compared to the recent studies done at √s_{\text{}NN}=2.76 TeV Pb+Pb collisions obtained by the ALICE collaboration.Speaker: Alex Mwai (Stony Brook University)
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HBT scaling results from UrQMD up to LHC energies 2hWe use the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) to explore HBT/Femtoscopic correlation in proton-proton and heavy ion collisions up to LHC energies. We discuss a) the scaling of HBT radii in proton-proton reactions at top LHC energies and b) the scaling of HBT radii from proton-proton to heavy-ion reactions from RHIC-BES to LHC energies for various systems. [1] G. Graef et al., J. Phys. G in print (2012) [2] Q. Li, G. Graef, M. Bleicher, Phys. Rev. C 85, 034908 (2012) [3] G. Graef et al., Phys. Rev. C 85, 044901 (2012)Speaker: Gunnar Gräf (Frankfurt Institute for Advanced Studies)
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Heavy Flavour Electron azimuthal anisotropy $v_2$ from 2- and 4-particle correlations in Au+Au collisions at $\sqrt{s_{\rm NN}} = $ 200, 62 and 39 GeV at STAR 2hHeavy quarks (charm and bottom) are produced early in the collisions and therefore are important probes of the hot and dense matter created in the reactions at RHIC energies. Electrons from semileptonic decays of heavy flavour mesons (so called non-photonic electrons, NPE) are the most feasible tool so far for studying heavy quarks in-medium interactions. NPE azimuthal anisotropy, $v_2$, is of particular interest because it provides additional means to discriminate between models which describe heavy quark in-medium interactions. In this presentation we will report the $v_2$ measurements using 2- and 4-particle correlations, $v_2\lbrace2\rbrace$ and $v_2\lbrace4\rbrace$, at $\sqrt{s_{\rm NN}} = $ 200, 62 and 39 GeV at STAR. Non-photonic electrons in this study are identified using three main STAR subsystems: Time Projection Chamber, Time of Flight Detector and Barrel Electromagnetic Calorimeter. $v_2\lbrace2\rbrace$ and $v_2\lbrace4\rbrace$ have different sensitivity to the flow fluctuations and so called nonflow (correlations not related to the reaction plane) - there is a positive contribution of fluctuation and nonflow to the $v_2\lbrace2\rbrace$ while, in the case of $v_2\lbrace4\rbrace$, nonflow is negligible and the effect of fluctuations is negative. Therefore $v_2\lbrace2\rbrace$ and $v_2\lbrace4\rbrace$ provide an upper and lower limit on the average azimuthal anisotropy of non-photonic electrons. Moreover, bottom/charm production ratio at lower energies is expected to be reduced compared to $\sqrt{s_{\rm NN}} = $ 200 GeV, therefore low $p_T$ NPE azimuthal anisotropy at $\sqrt{s_{\rm NN}} = $ 62 and 39 GeV would reflect charm $v_2$ better than at $\sqrt{s_{\rm NN}} = $ 200 GeV.Speaker: Dr Daniel Kikola (Purdue University)
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Heavy quark energy loss in p+p collisions at the LHC 2hOne of the most promising probes to study deconfined matter created in high energy nuclear collisions is the energy loss of (heavy) quarks. It has been shown in experiments at the Relativistic Heavy Ion Collider that even charm and bottom quarks, despite their high mass, experience a remarkable medium suppression in the Quark Gluon Plasma. In this investigation we study the energy loss for heavy quarks in high multiplicity proton proton collisions at LHC energies. Although the colliding systems are smaller than compared to those at RHIC (p+p vs. Au+Au) the higher energy might lead to multiplicities comparable to Cu+Cu collisions at RHIC and thus might lead to a deconfined phase. This gives rise to a non-negligible suppression of heavy quark yields in elementary collisions. We study the dependence of this phenomenon on various quantities, such as the deconfinement energy density and the multiplicity reached in proton proton collisions and discuss this measurement as a probe to pin down parameters of the deconfinement phase transition. This study is published in Phys.Rev.Lett. 107 (2011) 032302. (arXiv:1012.0764)Speaker: Dr Sascha Vogel (Frankfurt Institute for Advances Studies)
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Heavy quark production at forward rapidity in d+Au collisions at sqrt(s) = 200 GeV 2hThe measurement of single muons from the semi-leptonic decay of D and B mesons is a well-developed method for the study of heavy quark production at forward rapidity. Previous PHENIX results from p+p and Cu+Cu collisions at sqrt(s) = 200 GeV have reported the suppression of heavy quark production in central Cu+Cu collisions at rapidity = 1.65. The measurement of heavy quark production at forward rapidity using d+Au data is crucial for the determination of the initial state effects of heavy ion collisions, leading to an improved understanding of cold nuclear matter effects during the collision. The detailed status of the analysis will be presented.Speaker: Sanghoon Lim (Yonsei University)
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HEAVY QUARKONIA IN MEDIUM AS OPEN QUANTUM DISSIPATIVE SYSTEM, A WAVE FUNCTION BASED APPROACH 2hIn static picture a quarkonium bound state in deconfined medium is either completely dissociated above some threshold temperature or just stays in the specific state below the threshold. In contrast, some recent studies suggest that the static quark antiquark potential for describing bound quarkonia should include an imaginary part. This shows a finite life time of the bound state in the medium and initiate a quest for dynamical picture of the dissociation. The dynamical picture becomes more relevant when the medium is expanding and cooling down rapidly, as in the case of heavy ion collision. A possible general framework for this dynamics is to view the quarkonia as an open system. We have designed a novel approach, based on the wave function, to address the real time dynamics of heavy quarkonia in medium (thermally equilibrated or not) produced in heavy ion collision.Speaker: Mr Nirupam Dutta (Doctoral Student, Bielefeld University)
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Heavy-quark diffusion at the LHC within a UrQMD-hydrodynamical hybrid model 2hHeavy charm and bottom quarks provide an important probe of the transport properties of the quark-gluon plasma, created in heavy-ion collisions at the Large Hadron Collider (LHC). They are produced in the early hard collisions and then interact with the hot and dense medium, consisting of light quarks and gluons, undergoing a phase transition to a hot and dense hadron gas. Using a hybrid model of Ultrarelativistic Molecular Dynamics (UrQMD) and 3D hydrodynamics [1] to simulate the evolution of the hot and dense medium, we describe heavy-quark interactions with the medium in terms of a Fokker-Planck/Langevin framework with drag and diffusion coefficients based on a Dirac-Brueckner evaluation of the in-medium scattering-matrix elements using lattice QCD heavy-quark potentials for elastic light-heavy-quark scattering [2] or a phenomenological resonance-scattering model based on chiral and heavy-quark effective theory [3] to evaluate the nuclear modification factor, R_AA, and elliptic flow v_2 of D- and B-mesons in PbPb collisions at sqrt(s_NN)=2.76 TeV. The results are compared with recent data from the ALICE collaboration on R_AA and elliptic flow of single electrons, muond, and D-mesons. [1] H. Petersen, J. Steinheimer, G. Burau, M. Bleicher, H. Stöcker, Phys. Rev. C 78, 044901 (2008) [2] H. van Hees, M. Mannarelli, V. Greco, R. Rapp, Phys. Rev. Lett. 100 (2008), 192301. [3] H. van Hees, V. Greco, R. Rapp, Phys. Rev. C 73 (2006), 034913.Speaker: Dr Hendrik van Hees (Goethe University Frankfurt)
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High-Energy Nuclear Collisions and the QCD Phase Structure 2hOne of the most exciting goals for the field of high-energy nuclear collisions is to understand the phase structure of matter with partonic degrees of freedom especially the transition from hadronic phase to partonic phase, the quark-gluon plasma (QGP). It is believed that the QGP phase dominates the evolution briefly during the early time of the Universe. In high-energy nuclear collisions at RHIC, the new form of matter, strongly interaction quark-gluon plasma (sQGP), has been formed [1]. The question now is what is the structure of the QCD phase diagram. In this talk, we will report a systematic study of the freeze-out properties and collectivities as a function of collision energies. These studies were performed with the AMPT and URQMD models. The region where the hadronic interaction dominant in the QCD phase diagram will be identified within the model studies. References: [1] J. Adams, et al., STAR Collaboration, Nucl. Phys. A757, 102(2005)Speaker: Prof. Feng Liu () College of Physical Science and Technology, Central China Normal University, Wuhan, 430079, China)
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High-pT direct photons in nuclear collisions: from RHIC to LHC 2hWe discuss a production of direct photons at large transverse momenta p_T in nuclear collisions at different energies and rapidities corresponding to RHIC and LHC experiments. Direct photons are very convenient tool for investigation of nuclear effects since they are not expected to be accompanied by any final state interaction, either energy loss or absorption. Therefore, besides the Cronin enhancement at medium-high p_T and small isotopic corrections at larger p_T, one should not expect any nuclear effects. However, data from the PHENIX experiment at mid-rapidities demonstrate a significant large-p_T suppression in central d+Au and Au+Au collisions that cannot be induced by coherent phenomena (gluon shadowing, Color Glass Condensate). We demonstrate that such an unexpected result is a subject to the energy conservation constraints (ECC) in initial state multiple parton interactions. The corresponding suppression factor falls steeply with p_T and leads to rather strong decrease with p_T of the nuclear modification factor violating so QCD factorization. In the RHIC kinematic region at forward rapidities we include also coherent phenomena as an additional source of nuclear suppression. In the LHC energy range ECC effects are irrelevant at mid-rapidities, but they are going to be important with increasing rapidity. We study for the first time a relative contribution of both sources of nuclear suppression at different rapidities performing predictions that could be verified in the future by experiments at RHIC and LHC. We analyze also a contribution of gluon shadowing as a leading twist shadowing correction modifying nuclear effects especially at small p_T.Speaker: Jan Cepila (Czech Technical University (CZ))
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High-pT neutral pion nuclear modification in PHENIX detector 2hNeutral-pion spectra were measured at midrapidity ($|y|<0.35$) in AuAu collisions at sqrt{sNN} = 39 and 62.4 GeV and compared to earlier measurements at 200 GeV in the $1<p_T<10$ GeV/c transverse-momentum (p_T) range. The nuclear-modification factors (RAA) show significant suppression and a distinct energy dependence at moderate p_T in central collisions. At high p_T, RAA is similar for sqrt{sNN} = 62.4 and 200 GeV at all centralities. Perturbative-QCD calculations that describe RAA well at sqrt{sNN} = 200 GeV fail to describe the sqrt{sNN} = 39 GeV data, raising the possibility that the relative importance of initial-state effects and soft processes increases at lower energies. The x_T-scaling power-law exponent was determined for the Au+Au and p+p collisions in range of sqrt(sNN) = 39 - 200 GeV. Further studies of the azimuthal anisotropy of the particle production at sqrt{sNN} = 200 GeV for high-p_T shows the geometrical path length dependence up to p_T<16 GeV/c. The data are compared with the recent theory calculations.Speaker: Norbert Novitzky (Helsinki Institute of Physics (FI))
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Higher moments of Net Kaon multiplicity distributions at RHIC energies for the search of QCD Critical Point 2hThe Relativistic Heavy-Ion Collider (RHIC) , at BNL, has started its beam energy scan program by colliding high energy heavy-ions corresponding to baryonic chemical potentials within the range of 20 - 550 MeV. One of the main goals of this beam energy scan program is to locate the critical point which is postulated to lie at the end of the phase transition boundary between partonic and hadronic matter. Calculations on the lattice predict that the higher moments (such as standard deviation (σ), skewness (S) and kurtosis (k)) of the multiplicity distribution of the conserved quantities like the net-charge, net-baryon, net-strangeness are related to the corresponding susceptibi-lities and the correlation length of the system, presence of a Critical Point might result in divergences of the thermodynamic susceptibilities and correlation lengths. Here we report the measurements of the various moments (standard deviation (σ), skewness (S) and kurtosis (k)) and their products (kσ2, Sσ) of the net kaon multiplicity measured by the STAR detector at mid-rapidity for Au+Au collisions at 7.7-200 GeV center of mass energies. The energy and centrality dependence of higher moments and their products (such as Sσ and Kσ2) will be presented. Theoretical calculation, containing the non-CP physics from the HIJING models will be compared to the data.Speaker: amal sarkar (Indian Institute of Technology, Mumbai)
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Higher moments of net-charge multiplicity distributions at RHIC energies from STAR 2hTo prob e the critical p oint (CP) of QCD phase transition, the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory has undertaken the beam energy scan program, colliding high energy heavy-ions corresponding to baryonic chemical potentials within the range of 20 - 550 MeV. QCD based model calculations reveal that the correlation length of the system diverges at the CP. The higher order moments (such as standard deviation ($\sigma$), skewness (S) and kurtosis ($\kappa$)) of the net-charge, net-baryon and net-strangeness multiplicity distributions are related to the corresponding higher order susceptibilities and also to the correlation length of the system. The non-monotonic behavior of these higher moments as a function of colliding energy could be considered as a signal of the CP. The STAR experiment has taken data for Au+Au collisions at 200 GeV, 62.4 GeV, 39 GeV, 27 GeV, 19.6 GeV, 11.5 GeV and 7.7 GeV center of mass energies. Here we report the mid-rapidity measurement of the higher order moments of the net-charge multiplicity distribution using the STAR time projection chamber detector for above beam energies. The energy and centrality dependence of higher moments and their products (such as $\frac{\sigma^{2}}{M}, S$\sigma$ and $\kappa\sigma^{2}$) will be presented. The data will also be compared to Poisson expectations and Hadron Resonance Gas model calculationsSpeaker: NIHAR R SAHOO (Variable Energy Cyclotron Centre)
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Hot quarkonium spectral functions from QCD sum rules and the maximum entropy method 2hQuarkonia spectral functions at finite temperature are studied using QCD sum rules in combination with the maximum entropy method. This approach enables us to directly obtain the spectral function from the sum rules, without having to introduce any specific assumption about its functional form [1]. QCD sum rules incorporate finite temperature effects in form of changing values of the various gluonic condensates that appear in the operator product expansion. These changes depend on the energy density and pressure at finite temperature, which we extract from lattice QCD. As a result, we find that the charmonium states J/\psi, \eta_c, \chi_{c0} and \chi_{c1} dissolve into the continuum already at temperatures around or slightly above the critical temperature T_c [2]. As for bottomonium, it is found that \Upsilon(1S) and \eta_b survive in quark-gluon matter of temperature up to 2.5 -3.0 T_c, while \chi_{b0} and \chi_{b1} dissociate at 2.0 -2.5 T_c [3]. Furthermore, we find evidence for the melting of the excited states \Upsilon(2S) and \Upsilon(3S) in the region of T=1.5 -2.0 T_c [3]. [1] P. Gubler and M. Oka, Prog. Theor. Phys. 124, 995 (2010). [2] P. Gubler, K. Morita and M. Oka, Phys. Rev. Lett. 107, 092003 (2011). [3] K. Suzuki, P. Gubler, K. Morita and M. Oka, arXiv:1204.1173 [hep-ph].Speaker: Philipp Gubler (RIKEN)
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How do Jets Affect the Collective Flow of the Quark-Gluon Plasma? 2hIn this work we study how highly energetic jets affect the hydrodynamic evolution of the quark-gluon plasma in an event-by-event basis. This is done by the introduction of a source term [1] in the energy-momentum conservation equation that describes the evolution of inviscid hydrodynamics (with a realistic equation of state [2]). The source is parametrized in terms of the direction of the jet in the medium and its energy loss rate. The influence of jets on the QGP collective flow is systematically investigated using the Fourier coefficients of the azimuthal flow distribution computed at both RHIC and LHC energies. In addition, we discuss the structure of the two-particle correlation function taking into account both initial state fluctuations [3,4] and the effects of jets. While the propagation of jets in a smooth QGP has been extensively studied before, the interplay between the different sources of flow anisotropy (i.e, initial state fluctuations and jets) studied in this work poses some new questions about the hydrodynamical evolution of the QGP. For instance, can Mach cones consistently form in an event-by-event basis? Do the highly high energetic jets present at LHC lead to novel structures in the two-particle correlation function? In this presentation we intend to shed some light on such questions. [1] A.K.Chaudhuri and U.Heinz, Effect of jet quenching on the hydrodynamical evolution of QGP, Phys. Rev. Lett. 97, 062301 (2006); B.Betz, J.Noronha, G.Torrieri, M.Gyulassy and D.H.Rischke, Universal Flow-Driven Conical Emission in Ultrarelativistic Heavy-Ion Collisions, Phys. Rev. Lett. 105, 222301 (2010). [2] P.Huovinen and P.Petreczky, QCD Equation of State and Hadron Resonance Gas, Nucl. Phys. A 837, 26 (2010). [3] J.Takahashi, B.M.Tavares, W.L.Qian, R.Andrade, F.Grassi, Y.Hama, T.Kodama, N.Xu, Topology studies of hydrodynamics using two particle correlation analysis, Phys. Rev. Lett. 103, 242301 (2009). [4] Y.Hama, R.P.G.Andrade, F.Grassi, W.-L.Qian, Trying to understand the ridge effect in hydrodynamic model, Nonlin. Phenom. Complex Syst. 12, 466-470 (2009).Speaker: Rone Andrade (Universidade de São Paulo USP)
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How does longitudinal drag change the radiative energy loss rate? 2hJets propagating through dense matter are modified due to the scattering between the patrons of the jet with the constituents of the medium. Such scattering leads to an exchange of momenta between the medium and the jet, and has components that are both parallel and perpendicular to the direction of jet propagation. These scatterings introduce both drag and diffusion, and also change the rate of parton splitting leading to radiative energy loss. In all current calculations of jet modification, only the effect of transverse scattering (quantified by $\hat{q}$) on stimulated emission has been considered. The effect of longitudinal exchange, leading to a drag and diffusion of the produced patrons, is included separately. We compute, for the first time, the gluon emission rate from a hard quark in the presence of both transverse and longitudinal exchange. Depending on the size of the longitudinal drag and diffusion coefficients, longitudinal scattering is shown to influence the radiative energy loss of a hard quark in a dense medium in a non-intuitive way. Ramifications of this effect for the phenomenology of jet quenching in heavy-ion collisions will also be presented.Speaker: Guang-You Qin (Duke University/Wayne State University)
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Hydrodynamics at large baryon densities: Understanding proton vs. anti-proton v_2 from baryon number conservation 2hUsing hydrodynamics we explore the effects of the initial state, baryon stopping and baryon number transport on various observables such as spectra, elliptic flow and particle yields for heavy ion collisions at beam energies from sqrt{s_{NN}}=7.7 to 200 GeV. We find that observed phenomena such as the centrality dependent freeze out parameters as well as the apparent difference in particle and anti-particle v_2 can be explained by a collective hydrodynamic expansion, once baryon stopping and baryon number conservation are properly taken into account. We will further discuss how the various stages of the collision contribute to the p_{t} spectra, the mass dependence of T_{eff} and particle ratio fluctuations.Speaker: Dr Jan Steinheimer-Froschauer (Lawrence Berkeley National Laboratory)
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Identical kaon femtoscopic correlations in proton-proton and heavy-ion collisions at the LHC 2hFemtoscopic correlations allow one to measure the space-time characteristics of particle production thanks to the effects of quantum statistics for identical particles and final state interactions for both identical and non-identical particles. The main features of the femtoscopy measurements in heavy-ion collisions from SPS to RHIC and LHC are i) the increase of the correlation radii with increasing multiplicity of events and ii) the decrease of the radii with increasing pair transverse momentum/transverse mass. These are understood as a manifestation of strong collective flow. We report the measurement of correlations of two identical kaons (neutral and charged) in pp and Pb-Pb collisions by the ALICE experiment at the Large Hadron Collider (LHC). The increase of correlation radii for increasing multiplicity was observed both in Pb-Pb and pp collisions. The decrease of kaon radii for increasing transverse momentum was observed in Pb-Pb collisions. Similar behaviour of the radii was observed at high multiplicities in pp collisions. However at low multiplicity the behaviour of the radii is completely different. This observation may indicate a similarity between high multiplicity pp collisions and heavy ion collisions.Speaker: Matthew Donald Steinpreis (Ohio State University (US))
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Identification of charmed particles using multivariate analysis in STAR experiment 2hHeavy flavor particles, due to their production at the early stages of a collision, are of interest to study the properties of the matter created in heavy ion collisions at RHIC. Previous measurements of $D$ and $B$ mesons at RHIC[1, 2] using semi-leptonic probes show a suppression similar to that of light quarks, which is in contradiction with theoretical models including only a gluon radiative energy loss mechanism[3]. A direct topological reconstruction is needed to obtain a precise measurement of hadronic charmed meson decays. The remaining combinatorial background can be reduced by using modern multivariate techniques (TMVA)[4] that makes optimal use of all the information available. Comparison with classical methods and recent results[5] as well as the performances of some classifiers will be presented for the reconstruction of $D^{0}$ decay vertex ($D^{0} \rightarrow K^{-}\pi^{+}$) and its charge conjugate from Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV produced in 2007 using the Silicon Vertex Tracker and Silicon Strip Detector. \newline \newline [1]Adare A. et al., PHENIX Collaboration, Phys. Rev. C 84, 044905, 2011\newline [2]B.I. Abelev et al., STAR Collaboration, Phys. Rev. Lett 106, 159902, 2011\newline [3Y. L. Dokshitzer, D. E. Kharzeev, Phys. Lett. B 519, 2001\newline [4]A. Hoecker et al., arXiv:physics/0703039v5\newline [5]B. I. Abelev, et al, STAR Coll., arXiv:0805.0364\newlineSpeakers: Jonathan Bouchet (Kent State University), Joseph Vanfossen (Kent State University)
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Improving the $J/\psi$ Production Baseline in $pp$ and $pA$/d+Au Interactions at RHIC and the LHC 2hWe assess the theoretical uncertainties on the inclusive $J/\psi$ production cross section in the Color Evaporation Model using values for the charm quark mass, renormalization and factorization scales obtained from a fit to the charm production data [1]. We use our new results to provide improved baseline comparison calculations at RHIC. We also study the rapidity, $p_T$ and centrality dependence of cold nuclear matter effects on $J/\psi$ production in the CEM [2,3].\\[3ex] \noindent [1] R. E. Nelson, R. Vogt and A. D. Frawley, in preparation.\\ \noindent [2] R. E. Nelson and R. Vogt, in progress.\\ \noindent [3] D. McGlinchey, A. D. Frawley and R. Vogt, in preparation.Speaker: Prof. Ramona Vogt (LLNL and UC Davis)
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Incident Energy Dependence of Transverse Momentum Correlations in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 200 GeV in STAR 2hIt has been proposed that one signal of the critical point could be a non-monotonic change in the value of transverse momentum ( $p_t$ ) correlations as a function of centrality and/or incident energy [1]. Accordingly, we present results for two-particle $p_t$ correlations as a function of event centrality for Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV at RHIC, extending our previous work [2] to lower incident energies. The $p_t$ correlations will be calculated as a function of centrality and collision energy. We will study the energy dependence of the square root of the correlations ( $\sqrt{\Delta p_{t,i}\Delta p_{t,j}}$ ) divided by the event-‐wise average transverse momentum per event ( $<<p_t>>$ ). These results will be compared to measurements from other experiments as well as UrQMD model calculations. [1] H. Heiselberg, Phy. Rep. 351, 161 (2001) [2] STAR: Phys. Rev. C 72, 044902 (2005) [3] ALICE data: Stefan Heckel, Quark Matter 2011 [4] D. Adamova et al. [CERES Collaboration], Nucl. Phys. A727, 97 (2003)Speaker: John Novak (M)
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Influence of a realistic medium description including fluctuations on heavy quark observables 2hStrong jet quenching and high-pT hadron suppression as observed in relativistic heavy-ion collisions are striking experimental signatures for the formation of a deconfined QCD plasma, in which partons suffer from medium-induced energy loss. In particular, heavy quarks represent key probes for revealing the properties of the produced matter. In this talk, we discuss the consequences of a realistic medium description with fluctuating initial conditions on heavy-quark observables. For this purpose, we combine our Monte-Carlo approach to heavy-quark in-medium propagation MC@sHQ [1] with the full 3+1 dimensional fluid dynamic expansion from EPOS [2]. This allows for a consistent treatment of both the heavy-quark production and the collisional and radiative processes leading to the in-medium energy loss of heavy quarks. On an event-by-event basis, we report on RAA and v2 of D and B mesons for RHIC and LHC energies and confront our results with recent experimental observations. While with a simplified medium description [3] we find a too strong quenching for LHC conditions, the discrepancy can be resolved with a medium with initial fluctuations. Moreover, in EPOS a lattice QCD equation of state is used. This allows us to study the nature of the effective degrees of freedom present in the vicinity of the crossover transition, cf. [4], because a proportion of hadronic degrees of freedom above Tc would reduce the energy loss of heavy quarks. [1] P. B. Gossiaux and J. Aichelin, Phys. Rev. C 78 (2008) 014904 [2] K. Werner et al., arXiv:1203.5704, [3] P. F. Kolb and U. W. Heinz, In *Hwa, R.C. (ed.) et al.: Quark gluon plasma* 634-714 [4] C. Ratti et al., Phys. Rev. D 85 (2012) 014004Speaker: Dr Marlene Nahrgang
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Influence of background subtraction on jet reconstruction in heavy-ion collisions 2hIn order to get information about the characteristics of the medium produced in high-energy heavy-ion collisions using reconstructed jets, the effect of background subtraction has to be well under control. In this study, we address this issue by embedding jets in a heavy-ion event and then considering the influence of the subtraction method and of different backgrounds, characterized by different mean values and fluctuations, on the momentum imbalance and azimuthal distributions of the two leading jets in each event. Two different background modelings - a detailed Monte Carlo and a flexible toy model, and two subtraction methods - an area-based one similar to that used by ALICE and ATLAS, and a pedestal subtraction technique using the information in calorimetric cells resembling the one employed by CMS, are examined. We also consider the effect of quenching using the Q-PYTHIA Monte Carlo, and some additional background characteristics like elliptic flow. Our aim is to understand the possible differences between the results using the two reconstruction techniques, and how they react to the mentioned modifications of the signal and background.Speaker: Liliana Apolinário (Universidade de Santiago de Compostela)
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Influence of the medium evolution on heavy quark observables 2hOne of the most promising probes to study deconfined matter created in high energy nuclear collisions is the energy loss of (heavy) quarks. Theoretically however there exist various ambiguities, which still need to be resolved. In this work we investigate the dependence on the medium description of heavy quark energy loss. We find that by only changing the theoretical medium description and keeping the energy loss mechanisms intact one can expect huge discrepancies (up to a factor of 2!) in the very same theoretical approach. The medium descriptions we compare are widely used in the field of heavy ion physics, ranging from elliptic fireball models to hydrodynamics. Thus, by pinning down the energy loss mechanism with other existing approaches and measurements one can use this effect in order to differentiate between various medium descriptions and limit the parameter range of QGP modeling.Speaker: Dr Sascha Vogel (Frankfurt Institute for Advanced Studies)
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Inhomogeneous chiral phase in the QCD phase diagram and cooling of hybrid stars 2hRecently there has been much discussed the appearance of inhomogeneous chiral phases in the vicinity of the chiral restoration [1,2]. The critical end point should be the Lifshitz point, which properties have not been explored so much.Here we discuss an implication of inhomogeneous phase on cooling of hybrid stars. We consider the dual-chiral-density-wave (DCDW) specified by the spatially modulated quark condensates with amplitude \Delta and wave number q [1], and study the beta decay of quarks. Since the DCDW state can be represented as a chirally rotated state, the quark weak-current is accordingly transformed to have an additional phase factor which modifies the energy-momentum conservation at the vertex. The direct evaluation of the neutrino luminosity shows that it is proportional to \Delta^2q^2T^6, which exhibits a similar form to the pion cooling [3]. Since the DCDW phase develops only in the limited density region, this novel mechanism may give an interesting scenario that lower mass stars should be cooler than heavy-mass ones, which has been also proposed to explain the recent data of Cas A in the context of color superconductivity [4]. [1]E. Nakano and T. Tatsumi, Phys. Rev. D71 (2006) 114006. [2]D.Nickel, Phys. Rev. Lett. 103 (2009) 072301; Phys. Rev. D80 (2009) 074025. [3]O.Maxwell et al., Ap. J. 216 (1977) 77. [4]T. Noda, M. Hashimoto, Y. Matsuo, N. Yasutake, T. Maruyama, T. Tatsumi, arXiv:1109.1080.Speaker: Prof. Toshitaka Tatsumi (Department of Physics, Kyoto University)
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Initial conditions for fluid dynamics from a parton cascade model 2hThe initial conditions play a fundamental role in the fluid-dynamical modeling of the quark-gluon plasma (QGP) created in ultrarelativistic heavy-ion collisions. Many observables that are important in determining the properties of the QGP, such as elliptic flow (v2) and triangular flow (v3), appear to be generated mainly from the initial geometry of the energy density profile. Since the initial conditions remain undetermined, it introduces a large uncertainty in the extraction of the properties of the QGP. Typically it is assumed that the matter thermalizes and fluid dynamics can be applied after time of the order of $1$ fm/c after the initial nuclear collision. However, the matter itself can be created much earlier, and it undergoes pre-equilibrium evolution before fluid dynamics can be applied. In this work, we estimate the impact of the pre-equilibrium evolution of the QGP on the initial conditions for fluid dynamics using a parton cascade model. For the initial conditions for the pre-equilibrium evolution we use a realistic 6--dimensional parametrization of the initial single-particle distribution function $f(x, p)$ that reflect, e.g. the observed rapidity and multiplicity distributions at RHIC and LHC. Then, we solve the time evolution of this distribution using the relativistic Boltzmann equation, up to times of the order of 1 fm/c, for various values of partonic cross sections. The relativistic Boltzmann equation is solved using the BAMPS algorithm Ref. [1]. The main advantage of our approach is that we are able to compute, not only the energy density distribution at $t=1$ fm, but also the velocity and shear-stress tensor profiles, which, so far, are mostly unknown. [1] Z. Xu and C. Greiner, Phys. Rev. C 71 (2005) 064901; Phys. Rev. C 76, 024911 (2007).Speaker: Ioannis Bouras (University of Frankfurt a.M.)
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Initial state and 3D-hydrodynamic studies of heavy ion collisions with the proposed sPHENIX forward detector. 2hThe hydrodynamic behavior of the strongly interacting Quark-Gluon Plasma (QGP) has mostly been studied at mid-rapidity and important additional constraints on the longitudinal expansion of the medium are needed, in particular to help in constraining the initial state. The forward rapidity bulk medium initial state is also sensitive to low-x partons in one nucleus and high-x partons in the other. Local thermalization implies that different rapidity slices have different thermodynamic properties, including significantly higher baryon chemical potential. The PHENIX experiment is proposing a major suite of upgrades called sPHENIX that includes a new forward rapidity spectrometer with high precision tracking, particle identification, and calorimetry. The new detector is aiming to cover down to very forward angles and study hard probes such as heavy flavor, jets, photons and high pT hadrons. This poster will detail the layout of this new forward spectrometer and discuss how we will pin down the 3-dimensional hydrodynamic properties of the QGP.Speaker: Dr Cesar L. for the PHENIX Collaboration Silva (Los Alamos National Lab)
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Intense Magnetic Field Production in Non-Central Relativistic Nucleus-Nucleus Collisions 2hA very intense magnetic field is expected in non-central nucleus-nucleus collisions, and to reach ~ 10^14 T at the LHC energies. Not only being the strongest magnetic field in the Universe (cf. ~ 10^11 T on the surface of magnetars), various consequences of physics interests are in discussion, including chiral magnetic effects, synchrotron radiation, and non-linear behaviors of QED e.g. photon splitting and real photon decaying into dileptons. It should be however noted that the field itself is yet to be directly detected. We evaluate the expected intensity and life time of the field, based on cascade and static models, and its possible effects on real/virtual photon anisotropy and polarization, based on QED calculations of photon vacuum polarization tensors. A new approach to detect the field via direct virtual photon polarization is proposed and its experimental feasibilities at ALICE and PHENIX experiments are examined.Speaker: Kenta Shigaki (Hiroshima University (JP))
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Investigating the ridge structure in #Delta#eta-#Delta#phi correlations at STAR 2hTriggered di-hadron correlation studies using Au+Au collisions at #sqrt(S_{NN}) = 200GeV in STAR revealed a novel “ridge-like” structure in two dimensions (#Delta#eta, #Delta#phi) [1] for high p_{T} particles. Similar structure was also present in an inclusive un-triggered di-hadron correlation analysis [2]. We study the <p_{T}> evolution of un-triggered analysis by increasing the lower p_{T} cut of both charged particles. A smooth evolution of data is observed and our results reproduce the initial triggered analysis structure near <p_{T}> = 2.7 GeV/c. We further quantify the correlation structure evolution by fitting a model function. The model function emphasizes possible initial state fluctuation contribution via the use of higher harmonic model components; v_{n} (n=1,2,3,4) and the remainder is modeled via an asymmetric 2d Gaussian. Extracted harmonic parameters are compared to model predictions [3,4] and remainder is quantified via p+p data at #sqrt(S_{NN}) = 200GeV and charge dependent studies. [1] B. I. Abelev et al. (STAR Collaboration), Phys. Rev. C 80, 064912 (2009) [2] M Daugherity et al. (STAR Collaboration), J. Phys. G 35, 104090 (2008) [3] B. Alver et al., Phys. Rev. C 81, 054905 (2010) [4] C. Gombeaud et al., Phys. Rev. C 81, 014901 (2010)Speaker: Mr L. Chanaka De Silva (University of Houston)
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Investigation of a quark matter in hybrid stars 2hQuark matter is expected in the core region of neutron stars because of the central density is sufficiently high for nucleons to dissolve into quarks. The compact stars consist of not only nuclear matter but also hypeons and quarks, we call such stars "hybrid stars". However, the equation of state (EOS) is still not clear and many theoretical studies try to elucidate the EOS in the high density and/or temperature. The crust region of the stars consist of nucleus and nuclear matter. Therefore the inner region of the stars should have hadron-quark mixed phase. Nowadays it is pointed out that the inner structures would affect macroscopic phenomena of the star[1]. However, the inner structures are strongly depend on EOS of the matter. We show that the hadron-quark mixed phase should be restricted to a narrower region because of the finite-size effects and a quark matter region should appear in the central region[2]. The narrow region of the mixed phase seems to explain physical phenomena of neutron stars such as the strong magnetic field and glitch phenomena, and it would give a new cooling curve for the neutron star. References: [1] A. Kurkela, P. Romatschke and A. Vuorinen, Phys. Rev. D81, 105021 (2010); arXiv:1006.4062. [2] T. Endo, Phys. Rev. C 83, 068801 (2011).Speaker: Prof. Tomoki Endo (Division of Physics, Department of General Education, Kagawa National College of Technology, Japan.)
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Is the event plane dependent modification to jet-like correlations due to analysis biases or jet-medium interactions? 2hThe STAR results [1] from dihadron correlations as a function of the high-pt trigger azimuth relative to the event plane (phi_s) show a significant change from in-plane (phi_s~0) to out-of-plane direction (phi_s~90 degree). The near-side correlation is composed of two components: the jet-like correlation and the ridge; The former is found to be invariant over phi_s while the ridge is primarily observed in-plane. On the other hand, the away-side "double hump" is present only out-of-plane. It has been found that the recently characterized triangular flow does not change the qualitative conclusions [1]. However, the question remains, whether the observed phi_s dependent modification is due to analysis biases in flow background subtraction or jet-medium interactions. In this talk we analyze high-pt triggered dihadron correlations relative to the event plane in the AMPT (A Multi-Phase Transport) parton cascade model. The AMPT model, with its string melting, has been previously shown to reproduce some of the global phenomena seen in heavy-ion collisions, specifically flow [2]. We first obtain the near-side jet-like correlations from the difference of large and small delta-eta azimuthal correlations and find AMPT does not reproduce the STAR data. We then analyze the large delta-eta azimuthal correlation by subtraction of v2, v3, and v4 harmonic flows. The vn harmonic flows are obtained from two- and four-particle cumulant method and compared to the true average<vn> calculated using the initial geometry harmonic planes in AMPT. We assess the non-flow contributions in vn by the newly developed decomposition method [3], and address possible biases in our AMPT correlation analysis. We discuss their implications to the STAR data by comparing the vn subtracted event plane dependent dihadron correlations in AMPT to the STAR results. We discuss the remaining effects of jet-medium interactions in AMPT. [1] H. Agakishiev et al. (STAR Colloaboration), arXiv:1010.0690 [nucl-ex]. [2] Z.-W. Lin and C.M. Ko, Phys. Rev. C 65, 034904 (2002). [3] L. Xu, L. Yi, D. Kikola, J. Konzer, F. Wang, and W. Xie, arXiv:1204.2815 [nucl-ex].Speaker: Joshua Konzer
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Isolated photons in pp and Pb-Pb collisions at the LHC with the ALICE EMCal 2hPhotons are of great interest in relativistic heavy-ion collisions due to the fact that they do not interact strongly, and thus are used to make a tomographic view of those collisions. Of special interest are the directly produced high-transverse momentum photons. The ratio of their yield in Pb-Pb to pp collisions is sensitive to initial state effects. Furthermore, direct photons can be used tag the away-side parton in photon-jet or photon-hadron correlations studies. The application of isolation criteria to the selected photon candidates is an important experimental tool to suppress the contamination from decay photon, but also from fragmentation and Bremstrahlung photons. In this poster, we present isolated photon spectra in transverse momentum ranges between 15 and 50 GeV/c in pp and Pb-Pb collisions at center-of-mass energies of 2.76 and 7 TeV. The isolated photons are reconstructed in datasets triggered by the ALICE Electromagnetic Calorimeter.Speaker: Mauro Rogerio Cosentino (Lawrence Berkeley National Lab. (US))
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J/$\psi$ production in $\sqrt{s_{NN}}$ = 39 GeV and 62.4 GeV Au+Au collisions from STAR 2hThe Relativistic Heavy Ion Collider (RHIC) is built to search for the Quark-gluon Plasma (QGP) and to study its properties in laboratory through high energy heavy-ion collisions. J/$\psi$ suppression in heavy-ion collisions due to color screening of quark and anti-quark has been proposed as a signature of QGP formation. But other mechanisms are likely to contribute to the observed J/$\psi$ in heavy-ion collisions such as the cold nuclear matter effect, charm quark recombination, sequential suppression, and hot wind dissociation. Measurements of J/$\psi$ invariant yields at different collision energies and centralities can shed new light on understanding the interplay of these mechanisms for J/$\psi$ production and medium properties. In this presentation we will report the measurements of J/$\psi$ invariant yields as a function of transverse momentum (with $p_{T}$ coverage: 0-5 GeV/c at mid-rapidity) in Au+Au collisions at $\sqrt{s_{NN}}$ = 39 GeV and 62.4 GeV taken in 2010 from STAR with full Time-of-Flight detector and Barrel ElectroMagnetic Calorimeter detector in operation. Centrality dependence of J/$\psi$ production and nuclear modification factors will be presented. Comparisons among different collision energies and model calculations will be discussed.Speaker: Wangmei Zha (U)
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J/psi measurements at ALICE using EMCal-triggered events 2hJ/psi measurements can be performed with ALICE through the dilepton decay into electrons (for rapidity |y|<0.9) and muons (for rapidity -4.0<y<-2.5) pairs, in proton-proton, proton-nucleus and nucleus-nucleus collisions. J/psi measurements are very important in Pb-Pb as a probe of the Quark Gluon Plasma (QGP), in order to study mechanisms of suppression or regeneration. Proton-proton collisions are also important for the ALICE physics program, since they provide baseline results to be compared with Pb-Pb. The ALICE Electromagnetic Calorimeter (EMCal) extends the pt range of J/psi measurements, since it provides electron/hadron discrimination for higher pt values in comparison to other electron PID techniques in ALICE. The EMCal can also provide fast triggers for events containing high energy electrons. In this poster, the performance of J/psi measurements using EMCal triggered events will be shown, using results from proton-proton and Pb-Pb collisions taken in 2011.Speaker: Marcel Araujo Silva Figueredo (Universidade de Sao Paulo (BR))
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J/Psi suppression in high multiplicity proton-proton collisions at LHC energies 2hWe study charmonium physics in heavy-ion collisions within the framework of the non-equilibrium transport model UrQMD at SPS, RHIC and LHC energies. For pp collisions at LHC energies we find a considerable J/Psi suppression in dependence of the particle multiplicity.Speaker: Thomas Lang
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Jet measurements in proton-proton collisions at sqrt(s) = 7 TeV with ALICE experiment 2hCollimated sprays of particles associated with hard partons, jets, are an important tool in testing QCD and probing the hot and dense nuclear matter created in high energy heavy-ion collisions. Jets enable to study hard scattering, fragmentation and hadronisation and their modification in presence of a partonic medium with respect to baseline vacuum measurements with proton-proton collisions. We have analysed data from proton-proton collisions at sqrt(s) = 7 TeV measured by ALICE and reconstructed the inclusive spectra of charged particle jets at mid-rapidity using k_t and anti-k_t clustering algorithms. We will present the jet spectra corrected for detector effects using unfolding and the unfolding procedure will be discussed in detail. We will examine various properties of jets, such as their charged particle multiplicity or jet shapes, with comparison to theoretical predictions.Speaker: Michal Vajzer (Acad. of Sciences of the Czech Rep. (CZ))
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Jet Physics Simulations for the sPHENIX Upgrade 2hThe first stage of the sPHENIX upgrade focuses on the measurement of jet observables at RHIC energies. The enhanced acceptance and high rate capabilities of this upgrade allow for the measurement of a large set of jet observables, including dijet and gamma-jet properties, across a large kinematic range. The sensitivity of the proposed upgrade to the medium modification of such observables and the ability to test and constrain theoretical models will be presented.Speaker: Dr J. Ali Hanks (PHENIX)
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Jet pT spectra at high pT in PbPb collisions at a center-of-mass energy of 2.76 TeV with CMS 2hThe poster presents the jet response and inclusive pT spectra of jets reconstructed in PbPb collisions with the CMS detector at a center-of-mass energy of 2.76 TeV. The jets are found and reconstructed using both the calorimeters and the tracker system, through iterative cone and anti-kT algorithms, separately. The high-pT jet triggers and their efficiencies are studied for both PbPb and pp collisions at a center-of-mass energy of 2.76 TeV. Different unfolding methods are employed to obtain the true distribution of the observables utilizing PYTHIA+HYDJET Monte Carlo Simulation samples.Speaker: Ying Lu (University of Maryland (US))
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Jet Quenching and Holographic Thermalization 2hThe AdS/CFT correspondence has been widely used to study the jet quenching of hard probes traveling in the strongly-coupled plasma. Nevertheless, in most of studies, the hard probes were assumed to be created at the late time within the thermalized medium. To understand the thermalization of the medium and its influence on high-energy probes generated in the early time in the strongly-coupled scenario would entail further investigations. In the gravity dual, the thermalization of the medium corresponds to the gravitational collapse and the formation of a black hole. We utilize the AdS-Vaidya metric, which describes a falling mass shell, to analyze the isotropic thermalization. In WKB approximation, the dissipation of a high-energy jet traversing the medium can be characterized by the stopping distance of a massless particle falling along the null geodesic in the gravity dual. We find the stopping distance of an energetic probe in AdS-Vaidya spacetime is equal to that in AdS-Schwarzschild spacetime, which implies that a probe with the energy much greater than the thermalization temperature is not be sensitive to the thermalization process, at least in this idealized scenario. This is different from a gluon probe with finite energy represented by a falling string in the gravity dual, where the stopping distance is governed by the null geodesic starting below the boundary. We find that the stopping distance is increased in the presence of the thermalization process.Speaker: Di-Lun Yang (D)
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Jet-Hadron Azimuthal Correlation Measurements in pp Collisions at sqrt{s} = 2.76 TeV and 7 TeV with ALICE 2hIn heavy-ion collisions, jet properties are expected to be modified by the interaction with the hot and dense medium. The modification is strongly related with properties of hot and dense matter and the study of jet properties is a versatile probe for the properties of the QGP. However, in heavy-ion collisions it is difficult to recover the jet quenching effects at small particle momentum due to large backgrounds from thermal bulk in such a multi-body system. The measurement of hadrons with respect to a reconstructed jet allows to relate more directly the momentum and direction of the original parton to the distribution of its fragmentation products. The study of these correlations in pp collisions provides the baseline for similar measurement in Pb-Pb collisions. We will present results of Jet-hadron azimuthal correlation studies in pp collisions at 2.76TeV and 7TeV. These results provide information on the jet energy (or momentum), jet shape, distribution of constituent particles in jet and background level in these systems.Speaker: Dosatsu Sakata (University of Tsukuba (JP))
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Jpsi Transverse Momentum Distribution as a Sensitive Signature of the Quark-gluon Plasma 2hDifferent from the Jpsi yield which is almost identical at SPS, RHIC and LHC energies, the Jpsi transverse momentum distribution is sensitive to the nature of the medium and can be used to probe the quark-gluon plasma formation in heavy ion collisions. We calculated in a detailed transport approach the nuclear modification factor as a function of transverse momentum, the averaged transverse momentum as a function of the number of participants, and the elliptical flow at RHIC and LHC energies.Speaker: Pengfei Zhuang (Tsinghua University)
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Lack of modifications in jet-like correlations from d+Au to Au+Au collisions for trigger particle p_T in both jet and hydrodynamic domains measured by STAR 2hAngular correlations with respect to a back-to-back trigger pair of high-p_T hadrons with similar momenta (above 4 GeV/c) have shown no differences between d+Au and Au+Au collisions suggesting tangential emission of selected di-jets. In this talk we increase the p_T threshold of the leading hadron in the pair (8, 10 and 12 GeV/c) to vary the degree of the surface bias. The di-jet energy imbalance is assessed via the difference of total momenta in the same- minus away-side peaks, and the measured imbalance is over-predicted by path-length dependent models, while showing possible evidence of softening of jet fragmentation. We find no qualitative change in the same-side peak of 2+1 correlation. Removing the back-to-back partner maximizing the asymmetry, the 2+1 reduces to the ordinary dihadron correlation, where significant modification is indeed observed on the away-side but the near-side remains similar between the d+Au and Au+Au events, indicating surface bias. We further lower the trigger p_T to as low as 1.5 GeV/c, where hydrodynamic production of particles are thought to dominate and jet-like correlations are expected to diminish. However, we find the identical near-side correlation between d+Au and Au+Au persists. The data cannot be described by the AMPT and HIJING models, and challenge the particle production paradigm in relativistic heavy-ion collisions.Speaker: Hua Pei (University of Illinois at Chicago)
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Lambda-Lambda correlation in high-energy heavy-ion collisions 2hWe study Lambda-Lambda correlation in high-energy heavy-ion collisions based on the Lambda-Lambda interactions proposed so far. Lambda-Lambda interaction and the existence of H-dibaryon are long-standing problems in hadron physics. Since high-energy heavy-ion collisions at RHIC and LHC can be utilized as the exotic hadron factories [1], they would also provide information on exotic interactions such as Lambda-Lambda, Lambda-Sigma, Lambda-Xi interactions, which are important to understand neutron star matter EOS. We have analyzed recent STAR data [2] and find that small negative scattering length (1/a_0 < -1 fm^{-1}) and large effective range (r_{eff} > 3 fm) are favored for Lambda-Lambda interaction [3]. This is consistent with quark model interaction (fss2), recent boson exchange potential (NSC97), and old boson exchange potentials (ND, NF) with large hard-core radius. In the presentation, we first discuss how precisely we can constrain Lambda-Lambda interaction from heavy-ion data. We also discuss the effects of feed from heavier hyperons and coupling effects with Xi-N channel, and Lambda-Lambda correlation measured in (K-,K+) reactions [4]. [1] S. Cho et al.(ExHIC collab.), Phys.Rev.Lett.106, 212001 (2011). [2] Neha Shar et al.(STAR collab.), Acta Phys. Pol. B Proc. Suppl. 5, 593 (2012) [arXiv:1112.0590]. [3] A. Ohnishi, T. Furumoto, in preparation. [4] C.J.Yoon et al. (KEK-E522 collab.), Phys. Rev. C75, 022201 (2007); A. Ohnishi et al., Nucl. Phys. A670, 297c (2000).Speaker: Akira Ohnishi (Kyoto University)
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Light (anti)nucleus production in $\sqrt{\rm s_{\rm NN}}$$=$7.7-200 GeV Au$+$Au collisions in the STAR Experiment 2hIn the dense and high-temperature systems formed in relativistic heavy-ion collisions, final-state composites - light nuclei and antinuclei - are formed close to the freeze-out hypersurface. Their spectra, compared to those of the constituent (anti)nucleons, can be described by picturing the formation process as the coalescence of a number of nucleons that are close to each other in phase space. This makes the composite spectra sensitive to the distribution of the constituent nucleons in phase space. It also implies a sensitivity of the spectra to the local densities and flow velocities of the source. In the coalescence picture, specific ratios of these spectra provide information on the baryon densities and homogeneity volumes. The STAR experiment has collected data from Au$+$Au collisions at seven beam energies, $\sqrt{\rm s_{\rm NN}}$, ranging from 7.7 to 200 GeV. The particle identification is performed for transverse momenta from $\sim$0.3 to \raisebox{-0.6ex}{$\stackrel{>}{\sim}$}3 GeV/c using a combination of the ionization energy loss in the Time Projection Chamber and the time of flight. The spectra for (anti)protons, (anti)deuterons, and (anti)tritons at mid-rapidity, and the source information inferred from these spectra, will be presented and compared to several dynamic coalescence models.Speaker: W.J. Llope (Rice University)
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Long range forward-backward multiplicity correlations in proton-proton collisions at LHC energies with the ALICE detector 2hMultiple parton interactions are expected to produce large long-range multiplicity correlations in high energy proton-proton and nucleus-nucleus collisions. Color glass condensate models explain the long range forward-backward (F-B) correlations by introducing strong color fields extended longitudinally in rapidity. Clustering of color sources also leads to F-B correlations. The measurement of the long range rapidity correlations of the produced particle multiplicities may give us insight into the space-time dynamics of the early stages of the collision. We report on short and long-range multiplicity correlations for pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7.0 TeV in the ALICE experiment for minimum bias as well as for high multiplicity events. This measurement utilizes an absolute coordinate system and preserves the actual spatial separation of the particles. The F-B correlation strengths at 7 TeV for minimum bias events are compared to those of 0-10\% Au+Au collisions at 0.2 TeV from RHIC. Comparison to different event generators will be made. Beam energy dependence of the correlation strengths from ISR, Fermilab to LHC energies will be presented.Speaker: Sudipan De (Department of Atomic Energy (IN))
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Low mass di-electron production in Au+Au collisions at $\sqrt{s_{_{NN}}} = 19.6$ GeV at STAR 2hAn enhancement of low-mass di-electron production which is compared to expected yields from known hadron sources was observed by the CERES experiment at CERN SPS in 158 A GeV central Pb+Au collisions (sqrt(s)=17.3GeV). More recently, NA60 reported their di-muon measurements in 158 A GeV In+In collisions. The enhancement of di-muon at $M_{\mu\mu} < 1$ GeV/$c^{2}$ can be described by a broadened spectral function. At RHIC, PHENIX experiment observed a significant enhancement in the di-electron continuum in Au+Au collisions at $0.15 < M_{ee} < 0.75$ GeV/$c^2$ at low transverse momentum ($p_{T}$ < 1 GeV/c). The models, which describe the SPS di-lepton data, have not been able to consistently describe the PHENIX data in the low mass and low $p_{T}$ region. STAR has recently presented preliminary results on the di-electron production in Au+Au at 200 GeV[1] Which was made possible by the addition of full-coverage time-of-flight detector. The Beam Energy Scan program covering beam energies down to SPS energies, and STAR's large acceptance, allow for measurements that can provide invaluable insights in this subject. We will present the mid-rapidity di-electron measurements in the $M<1.2$ GeV/$c^{2}$ mass region in Au+Au collision at $\sqrt{s_{NN}}$ = 19.6 GeV taken in 2011 with the full Time-of-Flight detector coverage at STAR. The di-electron production will be compared to hadronic cocktail simulation. Comparisons to model calculations with in-medium vector meson modifications will be made. [1] Jie Zhao (for the STAR collaboration) 2011. J. Phys. G: Nucl. Part. Phys. 38 124134Speaker: Dr Huang Bingchu (Brookhaven National Lab)
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LPM effect as the origin of the jet fragmentation scaling in heavy ion collisions. 2hWe address a recent puzzling result from the LHC: the jet fragmentation functions measured in $PbPb$ and $pp$ collisions appear very similar in spite of a large medium-induced energy loss (we will call this ``jet fragmentation scaling", JFS). To model the real-time non-perturbative effects in the propagation of a high energy jet through the strongly coupled QCD matter, we adopt an effective dimensionally reduced description in terms of the $(1+1)$ quasi-Abelian Schwinger theory. This theory is exactly soluble at any value of the coupling and shares with QCD the properties of dynamical generation of ``mesons" with a finite mass and the screening of ``quark" charge that are crucial for describing the transition of the jet into hadrons. We find that this approach describes quite well the vacuum jet fragmentation in $e^+e^-$ annihilation at $z\geq0.2$ at jet energies in the range of the LHC heavy ion measurements ($z$ is the ratio of hadron and jet momenta). In QCD medium, we find that the JFS is reproduced if the mean free path $\lambda$ of the jet is short, $\lambda \leq 0.3$ fm, which is in accord with the small shear viscosity inferred from the measurements of the collective flow. The JFS holds since at short mean free path the quantum interference (analogous to the Landau-Pomeranchuk-Migdal effect in QED) causes the produced mesons to have low momenta $p \sim m$, where $m \simeq 0.6$ GeV is the typical meson mass. Meanwhile the induced jet energy loss at short mean free path is much larger than naively expected in string models.Speaker: Frasher Loshaj (S)
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Luminosity determination in pp and Pb-Pb collisions at the LHC with the ALICE detector 2hLuminosity is an essential ingredient for the measurement of the cross section of physical processes. Luminosity determination in ALICE at the LHC is based on the visible cross sections measured in dedicated calibration experiments (van der Meer scans). Besides serving as reference for the determination of integrated luminosities, the cross sections measured in van der Meer scans can, with suitable extrapolation, provide direct access to physical quantities such as the inelastic interaction cross section. Van der Meer scans have been performed at the LHC in pp collisions at sqrt(s) = 2.76, 7 and 8 TeV and in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. A detailed description of the ALICE setup and analysis will be given; the measurement uncertainties will be discussed and compared to the requirements of the ALICE physics program.Speaker: Emilia Leogrande (Universita e INFN (IT))
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Magnetic plasma and unusual confinmenets 2hConfinement phenomenon for a long time was associated with Bose-Einstein condensation (BEC) of cirtain magnetic objects. In a series of previous works we had shown that it is indeed the case for lattice monopoles, which in pure gauge theory are about as numeroous near $T_c$ as gluons. We can now show that with increasing number of quark flavors to $N_f\sim 10$ the deconfinement transition moves to much stronger coupling, and thus magnetic monopoles will dominate electric excitations. We will also speculate that ``unusual" magnetic objects can undergo BEC, as they known to do so in supersymmetric analogs of multi-flavor QCD.Speaker: Edward Shuryak (stony brook university)
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Measurement of charm and bottom yields in Au+Au collisions at PHENIX 2hHeavy quarks (charms and bottoms) are interesting probes with which to study the properties of quark gluon plasma (QGP). Heavy quarks are created by initial hard scatterings, and thus are good probe to investigate the full time evolution of heavy ion collisions. Due to their heavy mass, the energy loss within the QGP is expected to be different for heavy quarks than for light quarks. Therefore, the measurement of heavy quark yields from heavy ion collisions leads to greater understanding of parton behavior inside QGP. We installed the silicon vertex tracker (VTX) in the PHENIX detector in order to individually measure charm and bottom contributions to heavy flavor single electrons and have collected Au+Au in 2011 and p+p collision data in 2012. In this poster, we present the status of charm and bottom yield measurements from the Au+Au collision data.Speaker: Ryohji (for the PHENIX collaboration) Akimoto (University of Tokyo)
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Measurement of $R_AA(\Upsilon)$ at PHENIX 2hThe suppression of quarkonia in heavy ion collisions has long been thought to provide an indication of the temperature dependent Debye screening length of color charge in the quark gluon plasma. A large sample of Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV have been collected by PHENIX in 2010. Using the PHENIX measurement of Upsilon production in p+p collisions as a reference, we will present the preliminary measurement of nuclear modification factor for Upsilon(1S+2S+3S) at mid-rapidity.Speaker: Shawn Whitaker (Iowa State University)
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Measurement of energy dependence of $K/\pi$ fluctuation in STAR experiment at RHIC 2h\documentclass[prc,aps,nofootinbib,% tightenlines,superscriptaddress,floatfix, preprintnumbers]{revtex4} \usepackage{bbm} \usepackage{graphicx} \usepackage{amsmath} \usepackage{amsfonts,amsbsy} \usepackage{amssymb} \renewcommand{\thefigure}{\arabic{figure}} \newcommand{\ndyn}{\nu_{dyn}} \newcommand{\gc}{{\gamma-\mathrm{ch}}} \begin{document} \title{Measurement of energy dependence of $K/\pi$ fluctuation in STAR experiment at RHIC} \author{Zubayer Ahammed} \affiliation{Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata-700064, India} \collaboration{for the STAR collaboration} \maketitle \preprint{ } Event-by-event fluctuations in strangeness may reveal the nature of Quark Gluon Plasma(QGP) phase transition and can be used as a probe for QCD critical point \cite{1}. Dynamical fluctuations in $K/\pi$ at lower beam energy were reported to increase with decreasing $\sqrt{s_{NN}}$ \cite{2} while they remained constant at higher $\sqrt{s_{NN}}$. STAR results for the study of $K/\pi$ fluctuations have been reported earlier for Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 39, 62.4, 130 and 200 GeV\cite{3,4}.The results have been found to be independent of beam energy. In this poster, we report new results on event-by-event fluctuations in $K/\pi$ at midrapidity from 19.6 and 27 GeV Au+Au collisions. The use of Time Projection Chamber(TPC) and Time of Flight(TOF) detector allows particle identification up to $p_{T}$ $\sim${\it{1.6 GeV/c}}. The advantage of this large particle identification reach in momentum and using a collider facility for $K/\pi$ fluctuation studies will be discussed. The results will be compared with the prediction of a transport model(UrQMD) and statistical hadronization model \cite{5}. %The status of this analysis and some preliminary results for RHIC BES program will also be presented in the context of energy dependence of $\gc$ correlation.J.I Kapusta and Mekjien, Phys.\ Rev. D {\bf 33} 1304(1986). \begin{thebibliography}{5} \bibitem{1} J.I Kapusta and Mekjien, Phys.\ Rev. D {\bf 33} 1304(1986). \bibitem{2} S.V. Afanasiev et. al.(NA49 Collaboration), Phys.\ Rev.\ Lett {\bf 86}, 1965(2001). \bibitem{3} B.I. Abelev et. al.(STAR Collaboration), Phys.\ Rev.\ Lett {\bf 103}, 092301 (2009). \bibitem{4} Terrence J. Tarnowsky(STAR Collaboration), J.\ Phys.\ G {\bf G38}, 124054 (2011). \bibitem{5} Giorgi Torrieri, Nucl-th/072062(2007). \end{thebibliography} \end{document}Speaker: Zubayer Ahammed (Department of Atomic Energy (IN))
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Measurement of Low Mass Electron-Positron Pairs with ALICE Low Mass e+e--Pair 2hDirect photons are an important probe of the hot and dense medium created in heavy-ion collisions because they do not interact with the medium and therefore carry information of all stages of the collision. At low momenta, thermal emission, which would provide the ideal measurement of temperature of the quark-gluon plasma, is expected to dominate over other sources of direct photons. However, since the fraction of thermal photon is small, the measurement of direct photons is notoriously difficult due to the large background from hadronic decay photons. These difficulties can be overcome by measuring virtual photons detected as internal conversion into electron-positron pairs. ALICE uses its excellent tracking and particle identification capabilities at very low momenta to perform this measurement in the Pb-Pb collisions collected in 2011 at sqrt(s_NN) = 2.76 TeV. Details of the measurement and status of the analysis will be presented.Speakers: Christoph Baumann (Johann-Wolfgang-Goethe Univ. (DE)), Markus Kohler (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
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Measurement of net-charge fluctuations by ALICE at the LHC 2hCharge fluctuations are considered to provide a possible signature for the existence of the de-confined Quark Gluon Plasma phase (QGP). Charge fluctuations are sensitive to the number of charges in the system, thus the fluctuations in the QGP, with fractionally charged partons, are significantly different from those of hadron gas with unit charged particles. The study of charge fluctuations have been carried out by using the variable, ν(+−,dyn) which, by its construction, is free from the collisional bias, i.e., impact parameter fluctuations and fluctuations from the finite number of charged particles within the detector acceptance. The dependence of charge fluctuations on the rapidity windows for various centrality bins are analyzed for Pb+Pb collisions at √sNN = 2.76 TeV in the ALICE experiment at CERN-LHC. Furthermore the higher moments of net-charge distribution are examined. It has been demonstrated that higher moments as well as moment products are sensitive to the correlation length and directly connected to the thermodynamic susceptibilities computed in the Lattice QCD. We observe that the dynamical fluctuations, measured in terms of ν(+−,dyn), decrease while going from peripheral to central collisions. We examine the dependence of fluctuations, using the D-measure, on the pseudorapidity interval ∆η, which may account for the dilution of fluctuations during the evolution of the system. The higher moments like mean, sigma (σ), skewness (S), kurtosis (K) and the quantities like Sσ and Kσ2 of net-charge are estimated as a function of centrality. The experimental values are compared to the theoretical expectations for a hadron gas and a Quark Gluon Plasma (QGP). The results will be shown and discussed.Speaker: Satyajit Jena (IIT- Indian Institute of Technology (IN))
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Measurement of omega->3pi in pp collision at 7TeV with ALICE 2hThe $\omega$ meson is a promising probe to investigate the properties of the QGP. It is well known that the yield of high-p_t particles is suppressed in nucleus-nucleus collisions relative to that in pp collisions. The effect is attributed to the energy loss of the energetic parent partons traversing the created medium. Since $\pi^0$ and $\omega$ mesons have the same quark content (u and d), the comparison of the suppression between $\pi^$ and $\omega$ can provide information whether the energy loss occurs at the parton level or not. The ALICE detector covers a wide central region (|\eta|<0.9) to reconstruct charged particles and has two electro-magnetic calorimeters with good energy resolution. The $\omega$ meson is reconstructed in the $\pi^0\pi^+\pi^-$ channel in pp collisions at sqrt(s) = 7 TeV over a wide p_t range This is faciliated by a high-photon energy trigger. We discuss the trigger performance and cut optimization and present the latest results of the analysis.Speaker: Satoshi Yano (Hiroshima University (JP))
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Measurement of the J/Psi production cross section in ultraperipheral Pb-Pb collisions 2hThe results of the study of ultraperipheral (gamma-gamma and gamma-Pomeron) interactions are presented. The analysis was performed with the data recorded by the ATLAS experiment during LHC Pb-Pb run in year 2011. The data, taken at the beam energy of 2.75 TeV per nucleon, correspond to an integrated luminosity of 141/microbarn. Muon pairs, produced in pure electromagnetic two-photon interactions and in reactions of J/Psi photoproduction, were analyzed and the cross section of AA -> AA + mu+mu- reaction was measured. Another measurement of the J/Psi photoproduction cross section was carried out with the events accompanied by mutual neutron emission and triggered by Zero Degree Calorimeter.Speaker: Tomasz Bold (AGH Univ. of Science amp; Technology, Krakow)
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Measurement of the production of heavy- flavour decay electrons in pp collisions at sqrt(s) =2.76 TeV with ALICE 2hHeavy quarks, being produced in the initial stages of heavy-ion collisions, provide an excellent probe for the properties of the quark-gluon plasma (QGP). The expected in-medium energy loss of quarks is predicted to have a mass-dependence; however, recent results indicate that heavy-quarks lose more energy than expected. The measurement of electrons from heavy flavor decays provides insight into the energy loss of heavy quarks. In this poster, we present the measurement of the heavy-flavor electron cross-section at central rapidity in sqrt(s) = 2.76 TeV pp collisions in the transverse momentum range 2-12 GeV/c. The measurement in pp collisions provides the necessary baseline for comparison to heavy ion collisions and provides a test of perturbative QCD calculations of heavy quark production. The result is compared to FONLL perturbative QCD predictions.Speaker: Bernard Richard Hicks (Yale University (US))
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Measurements of anisotropic flow($v_n$, n=1,2,3,4) in Cu + Au collisions at 200 GeV from PHENIX 2hMeasurements of the anisotropic flow with different order harmonic coefficients ($v_n$, n=1,2,3,4) have played a pivotal role in the discovery of the strongly coupled quark-gluon plasma (sQGP) at RHIC. They are also important for the study of the viscous hydrodynamics and the extraction of the shear viscosity over entropy density ($\eta/s$). The anisotropic flow is strongly coupled with the medium density, initial geometry shape, and corresponding event-by-event fluctuation. All of these elements will come into play in a new way with the availability of Cu+Au collisions at RHIC. The flexibility of RHIC to collide asymmetric nuclei such as Cu + Au at 200 GeV can provide an asymmetric geometry and density both in the transverse plane and longitude, and therefore open a window to investigate the influence from initial geometry and density. It will also help us to probe the different hydrodynamics models and collision models and their properties. In this poster, I will present the work in progress for measuring the correlation between the different $v_n$ planes, from fast production data. Progress for the measurements of charged hadron $v_n$ as a function of centrality, transverse momentum and rapidity will also be presented.Speaker: Dr shengli huang (PHENIX Collaboration)
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Measurements of charged particle jet properties in pp collisions at sqrt{s} = 7 TeV using ALICE at the LHC 2hWe present results of a study of charged particle jet properties in pp collisions at $\sqrt{s}$ = 7 TeV using the ALICE detector. Jets are reconstructed using charged tracks at mid-rapidity with the anti-$\rm k_{t}$ [1] jet finding algorithm from FastJet. We will discuss the transverse momentum dependence of three jet properties: charged particle multiplicity, jet size, and radial distribution of transverse momentum about the jet direction for jets in the $\rm p_{t}$ range from 20 to 100 GeV/c. The results are compared with available model predictions. These measurements in $pp$ collisions will form the baseline for similar measurements in the more complex environment of A+A collisions. References [1] M. Cacciari and P. Salam, arXiv:0802.1189v1[hep-ph], 2008.Speaker: Sidharth Kumar Prasad (Wayne State University (US))
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Measurements of fully reconstructed jet cross-section and jet structure in pp collisions at \sqrt{s}=2.76 TeV with ALICE at the LHC 2hJet properties are expected to be modified in the dense, colored medium formed in Pb-Pb collisions at the LHC. To quantify such modifications, the measurement of reference distributions in pp collisions is essential. Jets are reconstructed from charged tracks measured in the ALICE central barrel, as well as the neutral energy measured in the Electromagnetic Calorimeter (EMCal). In this poster, we present a measurement of inclusive differential jet cross section in pp collisions at \sqrt{s}=2.76 TeV by combining Minimum-Bias and EMCal triggered events in ALICE. The bias of the EMCal trigger, which selects events with a shower in EMCal of energy greater than 3 GeV, is corrected to extract the jet cross-section. Two different jet cone radii R=0.2 and R=0.4 are used to reconstruct jets, and the ratio of the cross sections are reported. This provides first information on the jet energy profile.Speaker: Rongrong Ma (Yale University (US))
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Measurements of identified hadron spectra p+p interactions at 20, 31, 40, 80 and 156 GeV/c from NA61/SHINE at the CERN SPS. 2hPreliminary NA61/SHINE results on π+, π-, K+, K-, p and pbar spectra in p+p interactions at 20-158 GeV/c will be presented. NA61/SHINE at the CERN SPS is a fixed-target experiment pursuing a rich physics program [1]. Thanks to its large acceptance and excellent particle identification capability NA61/SHINE is well suited for performing high-precision particle production measurements in p+p, p+nucleus and nucleus+nucleus collisions. In this contribution inclusive spectra of π+, π-, K+, K-, p and pbar in p+p interactions at the SPS energies will be shown as a function of transverse momentum/mass and rapidity. The new data will be compared with the corresponding results of NA49 for central Pb+Pb collisions as well as with the predictions of Monte Carlo models. [1] N.Antoniou et al. [NA61/SHINE Collaboration], CERN SPSC-2007-019, (2007).Speaker: Szymon Mateusz Pulawski (University of Silesia (PL))
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Measurements of low-momentum thermal photons in Au+Au collisions with the PHENIX detector 2hPhotons are produced at all stages of a nuclear collision. Because of their extremely small interaction rate with the hadronic medium any information they carry about their production environment is accessible nearly undistorted in their final state. Photons are produced in hadronic decays, hard scatterings of initial state partrons, jet-photon conversions and from thermal radiation of the medium. At the lowest photon momenta hadronic decays and thermal production are the dominant sources. Any direct measurement of low-momentum photons is challenging in an electro-magnetic calorimeter due to large backgrounds and measurement uncertainties from hadron contamination in this energy regime. We will present a method for measuring real photons with external conversions with the PHENIX detector that allows measurements of these photons with improved systematic uncertainties.Speaker: Benjamin Bannier
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Microcanonical Tsallis statistics in jet fragmentation at LHC and LEP 2hFor the description of hadronic spectra in high-energy nuclear reactions, it is essential to understand the process of hadronisation. However, hadron creation is still an unsettled matter from the theoretical point of view. In the talk, I show that hadron distributions inside jets (fragmentation functions) created in s^1/2 = 7 TeV (LHC) proton-proton [1] and also in high-energy electron-positron [2] collisions can be described by a statistical jet-fragmentation model. This model combines microcanonical statistics and super-statistics induced by multiplicity fluctuations. The resulting scale dependence of the parameters of the model turns out to be similar to what was observed in electron-positron annihilations in Ref. [2]. [1] Phys. Lett. B 701: 111-116, 2011; arXiv:1101.3023 [2] Submitted to PLB, arXiv:1204.1508Speaker: Karoly Uermoessy (Hungarian Academy of Sciences (HU))
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Model-independent separation of flow and nonflow in relativistic heavy-ion collisions 2hAnisotropic flow, which arises from correlations to the common collision geometry, is sensitive to the early stage of the expansion of the medium created in relativistic heavy-ion collisions. Azimuthal anisotropy is measured by final state particle correlations and is thus contaminated by correlations unrelated to the common geometry (nonflow). The contamination of nonflow hampers further advancement in our study of relativistic heavy-ion collisions, in at least two areas: it prevents a more precise determination of the viscosity to entropy density ratio eta/s of the QGP medium from flow measurements, and it limits the power of jet-like correlations in probing partonic energy loss mechanisms where flow presents a background to be subtracted. Recently it has been shown that the measured two-particle correlation Fourier coefficients approximately factorize, and it was argued that this indicates the dominance of flow. In this talk we show by PYTHA simulations of p+p collisions that factorization approximately holds also for jet-like correlations and therefore is only a necessary but not sufficient condition for flow [1]. We suggest that nonflow factorization can in turn be used to disentangle flow and nonflow as a function of particle transverse momentum by performing a two-component factorization fit to Fourier coefficients [1]. However, such disentanglement is model dependent, so are all other experimental nonflow studies thus far. To revamp this, we present in this talk a novel, model-independent method to decompose \Delta\eta-dependent and independent correlations using two- and four-partice cumulants between \eta bins, exploiting the symmetry of flow about midrapidity in symmetric heavy-ion collisions [2]. The \Delta\eta-independent correlations are dominated by anisotropic flow while the \Delta\eta-dependent correlations can be identified as nonflow. We illustrate our method using the AMPT and HIJING event generators. We discuss our decomposed flow and nonflow from the models. We further discuss the applicability of our method in separating flow and nonflow in real data at RHIC and LHC. [1] Daniel Kikola, Li Yi, ShinIchi Esumi, Fuqiang Wang and Wei Xie. arXiv:1110.4809 [nucl-ex] [2] Lingshan Xu, Li Yi, Daniel Kikola, Joshua Konzer, Fuqiang Wang and Wei Xie. arXiv:1204.2815 [nucl-ex]Speaker: Dr Daniel Kikola (Purdue University)
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Models of the 3-D Initial Hydro State: The "Club Sandwich" Picture 2hThe large majority of observations made of high-energy heavy-ion collisions at RHIC and LHC have been within a narrow range at mid-rapidity. These have been greatly informative, of course; but they've provided a window only onto a central "slice" of the created medium, leaving the full 3-D picture of the collision as a relatively unexplored frontier. How the initially locally thermalized hydro state comes into being across three dimensions involves fundamentally new QCD physics, which we can hope to diagnose via measurements spanning wide ranges of rapidity and correlations across them. Here we present and discuss the so-called "Club Sandwich picture", an inclusive framework for describing and parameterizing 3-D initial energy density profiles, not based on any particular stopping mechanism but only on the general considerations of energy and momentum conservation and causality. It is proposed, that frameworks of this type can serve as a useful bridge between final-state observations of energy/momentum flow and new physics models for the initial medium creation mechanisms.Speaker: Dr Paul Stankus (Oak Ridge National Lab)
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Monte Carlo simulation studies of the elastic energy loss of high-energy gluons and light quarks in a strongly interacting medium 2hA strong suppression of heavy-flavor hadrons has been seen in ultrarelativistic heavy ion collisions at BNL-RHIC and CERN-LHC. This surprising result has challenged the view of gluon radiation dominating over elastic 2-to-2 processes as a cause of parton energy loss in a quark-gluon plasma. To study the effectiveness of elastic collisions as the suppression mechanism in detail, we have developed a sophisticated Monte Carlo simulation describing the non-eikonal propagation of high-energy gluons and light quarks interacting with the quarks and gluons from the expanding QCD medium. The partonic collision rates are computed in leading-order perturbative QCD, while four different scenarios are used to model the QCD medium: 1) a simple static model for case studies of energy loss probability distributions; 2) (1+1)-dimensional hydro with initial conditions from the EKRT model for modeling the central heavy ion collisions; 3) (2+1)-dimensional hydro with a smooth sWN profile obtained from the optical Glauber model for non-central collisions; and 4) event-by-event hydro with an eBC profile from the Monte Carlo Glauber model for a detailed study of the initial state density fluctuation effects. We compare our results with the neutral pion suppression observed in sqrt(s_NN)=200 GeV Au+Au collisions at RHIC and charged hadron suppression in sqrt(s_NN)=2.76 TeV Pb+Pb collisions in the LHC. We find that a model with purely incoherent collisions is not supported by the experimental data. In addition, the initial state density fluctuations are not observed to have a significant effect on the elastic energy loss.Speaker: Jussi Auvinen (University of Jyväskylä)
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Monte-Carlo study of jets in heavy-ion collisions 2hJets have proven to be an important observable of heavy-ion collisions at the LHC; recent analysis has also made jets an important probe at RHIC energies as well. Unlike the spectrum of single hadrons, the spectrum of jets is highly sensitive to $\hat{q}_{\perp}$, as well as being sensitive to partonic energy loss and radiative processes. We use MARTINI, an event generator, to study how finite-temperature processes at leading order affect single jet, dijet, and photon-jet observables. Finally, finite-temperature effects on the momenta of heavy quarks are simulated and compared with data for open heavy flavor mesons.Speaker: Clint Young (McGill University)
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Morphology of High-Multiplicity Events in Heavy Ion Collisions 2hWe discuss opportunities that may arise from subjecting high-multiplicity events in relativistic heavy ion collisions to an analysis similar to the one used in cosmology for the study of fluctuations of the Cosmic Microwave Background (CMB). To this end, we discuss examples of how pertinent features of heavy ion collisions including global characteristics, signatures of collective flow and event-wise fluctuations are visually represented in a Mollweide projection commonly used in CMB analysis, and how they are statistically analyzed in an expansion over spherical harmonic functions. If applied to the characterization of purely azimuthal dependent phenomena such as collective flow, the expansion coefficients of spherical harmonics are seen to contain redundancies compared to the set of harmonic flow coefficients commonly used in heavy ion collisions. Our exploratory study indicates, however, that these redundancies may offer novel opportunities for a detailed characterization of those event-wise fluctuations that remain after subtraction of the dominant collective flow signatures. By construction, the proposed approach allows also for the characterization of more complex collective phenomena like higher-order flow and other sources of fluctuations, and it may be extended to the characterization of phenomena of non-collective origin such as jets. J.J. Gaardhoje, P. Naselsky et al. See: arXiv:1204.0387v1 [hep-ph]Speaker: Prof. Jens Jorgen Gaardhoje (Niels Bohr Institute)
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Multiplicity and pseudo-rapidity distributions of photons at forward rapidity in STAR at RHIC energies 2hThe main goal of the STAR experiment at Relativistic Heavy Ion Collider (RHIC) is to study the properties of the QCD matter at extremely high energy density and parton density, created in the heavy ion collisions. Photons are produced at all stages of the colliding system and through decay of produced particles like neutral pions. The multiplicity measurement of photons on an event-by-event basis is an important measurement complementing the charged particle measurement in a heavy ion collision. Inclusive photon production at forward rapidity shows an energy-independent longitudinal scaling as observed at √sNN = 62.4 and 200 GeV [1,2]. Photons measurements at lower energies will be helpful in further testing the energy dependence of the longitudinal scaling. The Photon Multiplicity Detector in the STAR experiment measures inclusive photons in the pseudo-rapidity region −3.7 < η < −2.3. We will present the multiplicity and pseudo-rapidity distributions of photons in Au+Au collisions at √sNN = 39 and 19.6 GeV for different event centralities. These measurements will be compared with published results at √sNN = 200 and 62.4 GeV and with models. References [1] Bedangadas Mohanty, J.Phys.Conf.Ser.50:(2006) 319 [2] STAR Collaboration, Nucl.Phys.A 832(2009) 134Speaker: Ms Dronika Solanki (University of rajasthan)
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Neutral meson flow in Pb-Pb collisions at the LHC with the ALICE EMCal 2hA central goal of the heavy-ion program at LHC is to study the properties of the quark-gluon plasma (QGP). The azimuthal anisotropy of particle production is a sensitive tool to study the features of the QGP. The anisotropy is typically characterized by $v_2$, the second harmonic coefficient of the Fourier series expansion of the particle azimuthal distribution with respect to the reaction plane. The observed $v_2$ is believed to be sensitive to different particle production mechanisms. At low transverse momentum ($p_{\rm t}$) $v_2$ encodes the information of the expansion driven by the initial pressure gradients. At high $p_{\rm t}$ it may be caused by path-length dependent parton energy loss. At intermediate $p_{\rm t}$ it may be related to the mechanism of quark coalescence. In this poster, we present the $v_2$ measurements of $\pi^{0}$ and $\eta$ mesons using data from the 2011 heavy-ion run at the LHC. The neutral mesons are reconstructed using the ALICE Electromagnetic Calorimeter (EMCal), while the event plane is determined by the V0 detector. The measured $v_{2}$ is reported as a function of the transverse momentum for different centrality selections. In order to study the systematic uncertainty, the $v_2$ coefficient has been extracted using both the $dN/d#varphi$ method and invariant mass method. The determination of the event plane using different subdetectors in ALICE, as well as their resolution, are also explored and discussed.Speaker: Fengchu Zhou (Central China Normal University (CN))
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Neutral meson production spectra studies in pp collisions at 7 TeV with the ALICE EMCal 2hIn this poster, $\pi^0$ and $\eta$ spectra in pp collisions at sqrt(s) = 7 TeV from the ALICE 2010 and 2011 runs (extended calorimeter acceptance) will be presented. The neutral mesons are reconstructed via their two photon decay channel where both photons are measured with the ALICE EMCal. For the ALICE 2011 run both, minimum bias and EMCal triggered data, have been analyzed. A precise measurement of the production spectra requires a thorough understanding of the response of the ALICE EMCal. Details of the analysis are described, including comparisons of the EMCal response with Monte Carlo simulations in terms of energy non-linearity and resolution as measured in test beam data. Corrections and associated systematic errors will be described.Speaker: Paraskevi Ganoti (Oak Ridge National Laboratory - (US))
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Neutron Stars and Functional Renormalization Group 2hRecently a two-solar-mass neutron star was observed. This puts new constraints on effective models at zero temperature and high chemical potential. In our approach we include mesonic degrees of freedom as well as nucleons in the framework of the Functional Renormalization Group. In this way, fluctuations beyond the mean-field approximation are taken into account.Speaker: Mr Matthias Drews (Technische Universitaet Muenchen)
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New method for measuring longitudinal fluctuations and directed flow in ultrarelativistic heavy ion collisions 2hRecently significant effort is made to study azimuthal flow asymmetries in ultra-relativistic heavy ion reactions. At finite impact parameters the directed flow and the elliptic flow were dominant observables for many years. In head-on collisions there would be no reason to have an azimuthal or longitudinal asymmetry, nevertheless, new observations for the higher harmonics show [1] that even in central collisions there is a strong azimuthal asymmetry in the emitted hadrons, and this asymmetry arises from transverse fluctuations of the initial state. In addition in head-on collisions the third harmonic of the azimuthal distribution, v_3, exceeds the second one, v_2, and becomes the dominant harmonic component in accordance with large fluctuations. The fact that high harmonics, measured up to v_8, survive the fluid dynamical expansion indicates that the QGP fluid is almost perfect, and does not absorb high-harmonics. Fluctuations must also appear in the longitudinal direction, especially in peripheral reactions where the projectile and target spectators may not be exactly the same size. As a first step of our study, we estimate the Event-by-Event (EbE) c.m. rapidity fluctuations using a method based on Zero Degree Calorimeters (ZDC)s. In peripheral reactions one can check if significant correlation between the EbE c.m. rapidities measured in the TPC and via the ZDCs do exist. This then leads to the possibility to separate the flow characteristics arising from collective global asymmetries and from random fluctuations. The first v_1 measurements at LHC [2] were also arising dominantly from random fluctuations as both the even and odd rapidity combinations gave the same result. As a second step, with the aim to determine the global asymmetry component of the directed flow v_1, we propose that the participant system Event-by-Event shifted from the Lab. c.m. frame to the measurable participant c.m. rapidity EbE, thus removing or minimizing the effect of random longitudinal fluctuations. Then following the global asymmetry the "odd" component of the directed flow can be separated and identified using this method. This new method [3] enables us to separate fluctuating and the global symmetry components in the flow, which is important for the odd harmonics, especially for v_1 and v_3. Thus one can study experimentally the rotation effect [4] and the possible occurrence of the Kelvin-Helmholtz instability [5] in the globally symmetric component of the collective flow. [1] K. Aamodt et al., (ALICE Collaboration) Phys.Lett. B708, 249 (2012). [2] I. Selyuzhenkov et al. (ALICE Collaboration), J Phys. G 38, 124167 (2011). [3] L.P. Csernai, G. Eyyubova, V.K. Magas, arXiv:submit/0463514. [4] L.P. Csernai, V.K. Magas, H. Stöcker, D.D. Strottman, Phys.Rev. C84, 02914 (2011). [5] L.P. Csernai, D.D. Strottman, and Cs. Anderlik, arXiv:1112.4287 [nucl-th].Speaker: Gyulnara Eyyubova (University of Oslo (NO))
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New relativistic dissipative fluid dynamics from kinetic theory 2hStarting with the relativistic Boltzmann equation where the collision term is generalized to include nonlocal effects, and using Grad's 14-moment approximation for the single-particle distribution function, we derive equations for the relativistic dissipative fluid dynamics. We compare them with the corresponding equations obtained in the standard Israel-Stewart and related approaches. Our method generates all the second-order terms that are allowed by symmetry, some of which have been missed by the traditional approaches, and the coefficients of other terms are altered. The first-order or Navier-Stokes equations too get modified. Significance of these findings is demonstrated in the framework of one-dimensional Bjorken scaling expansion of the matter formed in relativistic heavy-ion collisions.Speaker: Amaresh Jaiswal (Tata Institute of Fundamental research, Mumbai)
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NLO updates of the EKRT model for central AA collisions at RHIC and LHC 2hThe EKRT model [1] which combines pQCD minijet production with the saturation of produced gluons and (ideal) hydrodynamics, has predicted the measured multiplicities in central A + A collisions both at RHIC and LHC remarkably well [2]. Also the published pT spectra of bulk hadrons (at RHIC) have been reproduced quite nicely [3]. We now bring this closed framework to NLO as rigorously as possible. In particular, we calculate the minijet transverse energy production by using the latest knowledge of nuclear parton distributions (nPDFs), the NLO sets EPS09 [4], and discuss how the nPDF uncertainties propagate into the computed hydrodynamical initial conditions as well as observable multiplicities. Regarding the NLO minijet production, we develop a new set of infra-red safe measurement functions and study their effect on the multiplicity systematics from RHIC to LHC. Our main goal here is to quantify the theoretical uncertainties and the predictive power of this NLO pQCD + saturation + hydrodynamics -framework. [1] K. J. Eskola, K. Kajantie, P. V. Ruuskanen and K. Tuominen Nuc. Phys. B 570 (2000) 379. [2] K. J. Eskola, P. V. Ruuskanen, S. S. Rasanen and K. Tuominen, Nucl. Phys. A 696 (2001) 715. [3] K. J. Eskola, H. Honkanen, H. Niemi, P. V. Ruuskanen and S. S. Rasanen, Phys. Rev. C 72 (2005) 044904 [4] K. J. Eskola, H. Paukkunen and C. A. Salgado, JHEP 0904 (2009) 065.Speaker: Mr Risto Paatelainen (University of Jyvaskyla, Finland)
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Non-linear QCD dynamics in photon-photon interactions at high energies 2hAt high energies the amount of gluons in a hadron is much larger than the amount of any other constituent, for example it is much larger than the amount of sea quarks. Therefore, at high energies the hadronic cross sections are basically a function only of the gluons distribution. The color dipole formalism applied to photon-photon collisions implies that, before interacting, each of the photons fluctuates in a pair quark-antiquark with a certain probability. The pair is colorless and it is also called Color Dipole. In a first approximation we can treat one of the pairs quark-antiquark as if it was a hadron and we can apply the evolution equations of QCD to determine its gluons distribution. Then the photon-photon cross section can be factorized as a product of two terms. The first one is the probabilities for each photon fluctuate in a color dipole and the second term is the dipole-hadron cross section. In order to determine the dipole-hadron scattering amplitude we used non-linear QCD dynamics. The non-linearity of the evolution equations implies that the gluons distribution inside the hadron saturates when a given kinematic regime is reached. The scale separating the saturation regime of the linear one is called Saturation Scale. When the saturation regime is reached it is expected that the gluons distribution form a new state of matter, the called Color Glass Condensate (CGC). The search for the CGC is still going on and it is expected that LHC, as well as the future eRHIC, will give us a definitive answer of its existence. In this work we applied the CGC approach to photon-photon collisions through the color dipole formalism. We calculated cross sections to photon-photon scattering and calculated structure functions of virtual and real photons. We proposed a new model to the dipole-dipole cross section and compared our results with a model available in the literature. Our calculations can be considered as predictions to observables that will be measured in a future linear collider.Speaker: Erike Cazaroto (University of Sao Paulo)
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Nonperturbative Heavy-Flavor Diffusion and Hadronization in a Hydrodynamic Description of Heavy-Ion Collisions 2hWe compute open heavy-flavor (HF) transport in relativistic heavy-ion collisions by combining a strong-coupling treatment in both macro- and microscopic dynamics (hydro and nonperturbative diffusion interactions) [1]. The hydrodynamic bulk evolution is quantitatively constrained by bulk and multi-strange hadron spectra and elliptic flow [2]. In the Quark-Gluon Plasma (QGP) phase, heavy-quark diffusion coefficients are taken from a non-perturbative $T$-matrix approach. The latter leads to resonance formation close to Tc which is implemented as a hadronization (recombination) mechanism on a hydrodynamic hypersurface. In the hadronic phase, the diffusion of HF mesons is obtained from effective hadronic theory [3]. We compute observables at RHIC and LHC for both HF mesons and non-photonic electrons. In particular, we suggest the R_AA and v_2 of the D_s mesons as a unique observable due to the coupling of charm to the strangeness enhancement in AA collisions [4], which allows to quantitatively test key components of our approach, including recombination and hadronic diffusion effects. References: [1] M. He, R. J. Fries and R. Rapp, arXiv:1106.6006 [nucl-th]. [2] M. He, R. J. Fries and R. Rapp, Phys. Rev. C85, 044911 (2012). [3] M. He, R. J. Fries and R. Rapp, Phys. Lett. B701, 445 (2011). [4] M. He, R. J. Fries and R. Rapp, arXiv:1204.4442 [nucl-th].Speaker: Dr Min He (Cyclotron Institute, Texas A&M University)
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Novel coherence effects in initial state medium induced gluon radiation 2hRadiative interferences in the multiparton shower is the building block of QCD jet physics in vacuum. The presence of a QCD medium is expected to alter this interference pattern. We investigate color coherence effects in the medium modification to the initial state radiation in a simple setup which allows to include these effects in a clean way. We derive the medium induced gluon spectrum of an ``asymptotic" parton which suffers a hard scattering and subsequently crosses a QCD medium. The angular distribution of the induced gluon spectrum gets modified when one includes interference terms between the incoming and the outcoming parton at finite angle. In the soft limit, we provide a simple and intuitive probabilistic picture which could be of interest for Monte Carlo implementations. We comment on the possible phenomenological consequences of this new mechanism of soft gluon radiation in nuclear collisions.Speaker: Mauricio Martinez Guerrero (Universidade de Santiago de Compostela)
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Observation of a difference in $v_{2}$ between particles and anti-particles in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7-62.4 GeV with STAR 2hThe RHIC Beam Energy Scan covers a wide range in the QCD phase diagram temperature vs. baryon chemical potential. A phase transition between the Quark Gluon Plasma and the hadron gas phase is expected in this region of the QCD phase diagram. The elliptic flow $v_{2}$ is one of the observables which is sensitive to the pressure gradients in the initial stage of heavy-ion collisions. Hence it can provide important information about the properties of the fireball in the early stage of heavy ion collisions. Elliptic flow measurements at midrapidity from Au+Au collisions at \\ $\sqrt{s_{NN}}=$ 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV for identified hadrons ($\pi^{\pm}$,$K^{\pm}$, K$_{s}^{0}$, $p$, $\bar{p}$, $\phi$, $\Lambda$, $\bar{\Lambda}$, $\Xi^{-}$,$\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$) are presented. We observe a significant difference in $v_{2}$ between particles and corresponding anti-particles at the lowest energies of the beam energy scan. Baryons show a larger difference compared to mesons. The centrality, particle species and energy dependence of the difference will be presented. Furthermore we compare the data to several models and discuss their implications.Speaker: Alexander Schmah (Lawrence Berkeley National Lab)
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Observation of identical "near-side" jet-like correlations in d+Au and Au+Au collisions at low trigger $p_T$ by STAR 2hParticle production mechanisms vary with $p_T$. At low $p_T$ soft processes dominate whereas hard processes dominate at higher $p_T$. Experimental data has shown drastic change from d+Au to Au+Au collision in $p_T$ spectra, collective phenomena, and baryon/meson ratio at intermediate $p_T$. This indicates that the relative mixture of particles produced by hard and soft processes differ between Au+Au and d+Au at a given, relatively low $p_T$ (< 2.0GeV). It is therefore expected that the dihadron correlations will differ between d+Au and Au+Au with relatively low trigger particle $p_T$. In this talk we present the near-side jet-like correlations in d+Au and Au+Au collisions at 200 GeV by STAR. The jet-like results are obtained by the difference of small and large \Delta\eta correlations. We report the findings as a function of trigger and associated particle $p_T$, collision centrality, and Event Plane trigger orientation. We find the $/sqrt{S_{NN}}=200$GeV d+Au and Au+Au near-side correlations to be identical even at trigger $p_T$ as low as 1.5 GeV/c. The AMPT and HIJING models do not describe the data. Our results seem to challenge the current understanding of particle production mechanisms in relativistic heavy-ion collisions.Speaker: Joshua Konzer
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Obtaining full vn distributions at the LHC 2hThe large multiplicities at the LHC potentially permit azimuthal flow to be accurately determined on an event by event basis in heavy-ion collisions. I will discuss methods one can obtain full vn distributions from such measurements. In particular, any measurement of event-wise flow will be subject to statistical smearing, and I will review unfolding techniques to recover the true vn distribution. The methods will be applied to various initial state models, such as Monte Carlo Glauber. I will also discuss the effect of non flow and data driven techniques to remove it. Such potential measurements will shed light on the full nature of vn fluctuations, and provide key constraints to the theories of initial conditions.Speaker: Anthony Robert Timmins (University of Houston (US))
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on QGP signals in high energy pp collisions 2hWe will address the possibility of QGP formation in pp at 7TeV and 14 Tev with given life scan and size of QGP based on quantitative model estimation and constrained with all available data at LHC from the four collaborations. Then discuss the possible QGP signals in pp collisions, which certainly differ to the QGP signals in AA collisions. To theoreticians: Most of you think QGP formation is possible at high energy pp collisions. But why not do some quantitative calculations and give helpful references to the experimental exploration. To experimentalists: The employment of hydrodynamics in pp looks so unreliable. But don't forget at the beginning of hydro employment in AA some years ago, it looked the same unreliable. Nowadays the widely employment of hydro have helped us learn so much about the nature of the matter created in high energy heavy ion collisions. It is a fact that the diference between a high-multiplicity 7TeV pp system and a 200AGeV AuAu system is much much smaller than the difference between a 200AGeV AuAu system and a Moore of any kind of matter. So be open to take hydro employment in pp ---it may be useful references for you! The impact of QGP formation in pp is unknown, and waiting for our exploration.Speaker: Fuming Liu (Central China Normal University)
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On the Nature and Composition of the low-lying scalar mesons 2hWe follow chiral effective model [1] of a quarkonia nonet and a tetraquark nonet as well as a complex iso-singlet (glueball) field to study the lowest lying scalar mesons on the basis of chiral symmetry and UA(1) symmetry. By virtue of the isospin symmetry, the isospin 1 and isospin 1/2 physical states are assumed to have two and four bare quark components whereas I = 0 physical scalar and pseudoscalar mesons are assumed to have all the three bare components. We find that the model can accommodate the mass spectra of low-lying states quite well. Based on our result, we will discuss on the nature of the lowest iso-scalar f0(600) or sigma meson as well as the possible scalar and pseudoscalar glueball candidates. Referece: 1. Tamal K. Mukherjee, Mei Huang and Qi-Shu Yan, arXiv:1203.5717 [hep-ph].Speaker: Tamal Kumar Mukherjee (Institute of High Energy Physics, TPCSF)
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Open heavy flavor and J/psi at RHIC and LHC within a transport model 2hThe production and space-time evolution of heavy quarks and J/psi in the quark gluon plasma is studied within the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS). An updated version of BAMPS is presented which allows interactions among all partons: gluons, light quarks and heavy quarks. Heavy quarks, in particular, interact with the rest of the medium via binary and radiative scatterings with a running coupling and a more precise Debye screening which is derived from hard thermal loop calculations. We compare our results of the elliptic flow and nuclear modification factor not only to experimental data of heavy flavor electrons at RHIC, but also to LHC data of heavy flavor electrons, muons, D mesons, and non-prompt J/psi. The latter two are in particular sensitive on the mass difference of charm and bottom quarks. Where no data is available yet, we make predictions for those observables. Furthermore, results on J/psi suppression are reported for central and non-central collisions, taking cold nuclear matter effects and the dissociation as well as regeneration of J/psi in the quark-gluon plasma into account.Speaker: Jan Uphoff (Goethe University Frankfurt)
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Parton energy loss and modified beam quark distribution functions in Drell–Yan process in p +A collisions 2hWithin the framework of generalized collinear factorization in perturbative QCD (pQCD), we study the effect of initial multiple parton scattering and induced parton energy loss in Drell–Yan (DY) process in proton–nucleus collisions. We express the contribution from multiple parton scattering and induced radiative energy loss to the DY dilepton spectra in terms of nuclear modified effective beam (anti)quark distribution functions. The modification depends on the quark transport parameter in nuclear medium. This is similar to the final-state multiple parton scattering in deeply inelastic scattering (DIS) off large nuclei and leads to the suppression of the Drell–Yan cross section in p + A relative to p + p collisions. The modifications to (anti)quark distribution functions from (anti)quark-antiquark double scattering are shown to be determined by the (anti)quark distribution density in the medium. The asymmetry in quark and antiquark distributions in nuclei will lead to different modifications of quark and antiquark distribution functions inside the beam hardon. We also calculate DY spectra in p + A collisions and find the nuclear suppression due to beam parton energy loss negligible at the Fermilab energy Elab = 800 GeV in the kinematic region as covered by the E866 experiment. Most of the observed nuclear suppression of DY spectra in E866 experiment can be described well by parton shadowing in target nuclei as given by the EPS08 parameterization. The effect of beam parton energy loss, however, becomes significant for DY lepton pairs with large beam parton momentum fraction or small target parton momentum fraction.Speaker: Mr Hongxi Xing (Institute of Particle Physics, Central China Normal University)
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Performance of PHENIX Silicon Vertex Tracker(VTX) 2hThe PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has been upgraded by installing a Silicon Vertex Tracker (VTX). The VTX has been developed for heavy flavor (charm and bottom) measurements and dedicated to precise tracking of primary and secondary vertices. Resolution of primary vertex reconstruction and distance of closet approach (DCA) to distinguish secondary particles from in-flight decays are required several ten microns. In this way, we will be able to statistically separate the heavy-quark production of charm and beauty. In this poster, we will discuss the tracking performance of VTX: resolution of primary vertex and DCA measurements. Performance of alignment and tracking efficiency will be also presented.Speaker: Hidemitsu Asano (Kyoto Univ.)
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Performance of the Muon Telescope Detector in STAR at RHIC 2hA larger area of muon telescope detector(MTD) at mid-rapidity will provide excellent muon identification and trigger capabilities at mid-rapidity in the high-luminosity era at RHIC. This novel and compact detector can provide crucial measurements for many exciting physics perspectives. We can measure different Upsilon states and J/psi over a broad transverse momentum range through di-muon decays to study color screening features. The measurment of e-muon correlations can distinguish heavy flavor contributions from initial lepton pair production. The construction of the MTD at STAR has been started. In 2012, about 10% of the full system have been installed in STAR and taken data smoothly. In this poster, we will report the performance of the MTD in 2012 including its trigger capabilities,spatial, and timing resolution. Physics capabilities such as e-muon correlations will also be discussed.Speaker: Chi Yang (U)
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Performance simulations of a super compact forward electromagnetic calorimeter 2hWe present a performance study of a compact electromagnetic calorimeter meant to serve in a forward region (2 < eta < 4.5) in collider experiments in pp, pA and AA collisions. This kinematic region at LHC energies allows one to study very low Bjorken x physics. Measurement of direct photons in this region enables one to improve the precision of (nuclear) parton distribution functions. Our design is a scintillator-tungsten calorimeter with optical readout aimed at measuring high energy (1 < E < 1000 GeV) photons. We study its performance with Geant model. We present the design spatial energy resolution. Main contaminant of the photon yield in this kinematic domain are the secondary photons from pi0 decays, which account for more than half of the inclusive photon yield. We present pi0 rejection efficiency using cluster shape and depth energy deposition. Such device allows study of other effects in this kinematic region, such as jet measurement and jet quenching in the nuclear medium in pA and AA collisions and suppression driven by the coherence effects.Speaker: Libor Skoda (Czech Technical University (CZ))
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Perturbations on Top of the Fireball 2hWe study the effect that perturbations and their propagation through the medium have in the final particle distributions of heavy ion collisions. Our work is constrained to central collisions only, where the medium can be described by the solution to conformally invariant hydrodynamics developed by Gubser and Yarom, which is a generalization of Bjorken flow where the boost-invariant medium expands both in the longitudinal and the radial directions. When perturbations are added to the background the linearized hydrodynamic equations can be solved and the solutions for different modes can be summed up to form an initial point-like perturbation, that can be evolved until freeze-out. We use a similar procedure to study jets traversing the medium. Cases with different viscosities and different initial positions are considered and the Cooper-Frye prescription is used to calculate the final particle distributions.Speaker: Pilar Staig (Stony Brook University)
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Perturbative calculation in 1+1dimensional relativistic viscous hydrodynamics 2hWe discuss the evolution of the fluctuation in the initial conditions of entropy densities (energy densities) using 1+1 dimensional hydrodynamic calculations. We explore not only the evolution of the fluctuation but also the origin of it. If the local thermal equilibrium is established at early time of the heavy ion collision and the mean free path of produced particles is sufficiently short, then the later evolution of the system may be described by relativistic hydrodynamics. Most of studies have been performed with ideal hydrodynamics, but it is necessary to take into account of viscosity effect in hydrodynamical expansion to understand experimental data in detail. In particular, we focus on the dynamics along the collision axis and investigate how the viscous effects appear in evolution of the fluctuation in the framework of perturbation with respect to the bulk and shear viscosities. Assuming that the bulk and shear viscosities are small we calculate the entropy production during hydrodynamic evolution and the initial condition dependence of it. Here we use the Bjorken's solution for the ideal part (0th-order) in our perturbative approach and show detail calculated results.Speaker: Kyohei Fukuda (Nagoya)
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PHENIX $J/\psi$ measurement in Au+Au collisions at $\sqrt{s_{NN}}=$ 39 and 62 GeV 2h$J/\psi$ production is considered as one of the very important probes for studying the properties of quark-gluon plasma (QGP). PHENIX observed a large suppression of $J/\psi$ production in Au+Au collisions at $\sqrt{s_{NN}}=$ 200 GeV in comparison with binary collision scaled p+p collisions. The level of this suppression is similar to that observed in other energies in CERN-SPS and LHC. PHENIX also took $J/\psi$ data from Au+Au collisions at $\sqrt{s_{NN}}=$ 39 and 62 GeV in 2010. This data allow us to explore the energy dependent suppression level in order to disentangle the important contributing factors of $J/\psi$ production. We will present the $j/\psi$ $R_{AA}$ results at 39, 62.4 GeV in comparison with our previously published 200 GeV results.Speaker: Mr Abhisek Sen (Georgia State University)
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PHENIX $v_{2}$ measurement of single electrons from heavy flavor meson decays in Au$+$Au collision at $\sqrt{s_{NN}}$=62.4GeV and charm beauty separation using VTX at 200GeV 2hThe measurement of azimuthal anisotropy $v_{2}$ of single electrons from semi$-$leptonic decay of open heavy flavor mesons in PHENIX experiment has provided important understanding of the property of the quark gluon plasma, especially the geometrical dependence of partonic energy loss. PHENIX results of $v_{2}$ in Au$+$Au collision at $\sqrt{s_{NN}}$=200GeV for heavy-flavor decays are comparable to the $v_{2}$ measurements of other hadrons. This indicates that both the flow and the energy loss characteristics in heavy quarks are similar to light quarks, which is not well understood. We extend the PHENIX systematic study of azimuthal anisotropy by reducing the beam energy to $\sqrt{s_{NN}}$=62.4GeV. At this energy, the medium formed in Au$+$Au collisions is expected to have a lower energy-density. However, we will show that the heavy flavor electron $v_{2}$ at the lower beam energy is similar within the experimental uncertainties to the higher beam energy result. All the current PHENIX heavy flavor $v_{2}$ measurements are a mixture of charm and beauty. With the new detector - Silicon Vertex Tracker (VTX) installed in run11, we are able to measure $v_{2}$ separately for charm and beauty. The status of $v_{2}$ measurements separating single electrons from semi$-$leptonic decay of D and B mesons using the VTX will be presentedSpeaker: Lei Ding (I)
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Phi meson production in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV at the CERN LHC with ALICE 2hStrangeness production provides one of the key observables to characterize the hot and dense state of strongly interacting matter produced in high-energy nuclear collisions. To access this information, ALICE measured phi meson production both in proton-proton and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV in the dimuon channel, in the rapidity region 2.5 < y < 4. Thanks to these measurements, the nuclear modification factor of the phi meson can be extracted at the LHC energies. Preliminary results of the analysis will be presented, and the future perspectives for the study of low mass dimuon production in Pb-Pb collisions will be discussed.Speaker: Antonio Uras (Universite Claude Bernard-Lyon I (FR))
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phi-meson and Multi-Strange Hyperon Production at FAIR Energies from Transport Model in Heavy Ion Collision 2hThe study of phi meson and multi-strange production in heavy ion collision are the most interesting observables for exploring the new phase of matter named Quark Gluon Plasma. We will investigate the phi-meson and multi-strange production at FAIR energies using transport models like Ultra Relativistic Quantum Molecular Dynamics (UrQMD)[1] and A Multi Phase Transport Model (AMPT)[2]. The UrQMD model is based on a microscopic transport theory where there is phase space description of the reactions and resonance decays included. The AMPT is based on minijet formation. In this paper we present the measurement of elliptic flow (v2) of phi-meson and hyperon in Au-Au collisions at lab energies 10 GeV,25GeV and 35 GeV. References [1] S.A. Bass et al., Prog. Part. Nucl. Phys. 41 255 (1998). [2] Zi-Wei Lin et al., Phys. Rev. C 72, 064901 (2005)Speaker: Mr Mukesh Mukesh Kumar Sharma (University Of Jammu)
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Photon and Dilepton Emission from the Hadronization Process in Heavy Ion Collisions 2hA new source of photon and dilepton emission from nuclear matter undergoing phase transition from partonic to hadronic degrees of freedom is studied. Electromagnetic radiation can be emitted when quark antiquark pairs recombine into pions and other hadrons. The photon and dilepton production rates are found to be comparable to those in quark gluon plasma and hadronic matter around the critical temperature. We compute the photon and dilepton yields from such processes for Au+Au collision at RHIC(\sqrt{s}=200GeV) by convoluting the rates with a hydrodynamic simulation of the system. A comparison of the results to PHENIX and STAR measurements shows that dileptons from hadronization processes could partially explain the excess of low mass dilepton. The transverse momentum spectrum exhibits a smaller effective temperature than the QGP contribution. The elliptic flow of dileptons from the hadronization process behaves similar to the elliptic flow of dileptons from hadronic matter. Photon yields from these processes are not found to be important compared to QGP emission.Speaker: Mr Guangyao Chen (Cyclotron Insitute and Department of Physics&Astronomy, Texas A&M University)
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Photon Reconstruction in the sPHENIX Electromagnetic Calorimeter 2hThe initial stage of the sPHENIX upgrade detector at RHIC will focus on the measurement of jet observables, such as gamma-jet properties, withhigh statistics over a large kinematic range. We have studied several key performance parameters of the envisioned electromagnetic calorimeter. In this poster we will present the studies of the photon identification in the presence of the particle densities found in Heavy-Ion collisions.Speaker: Dr Martin Purschke (BROOKHAVEN NATIONAL LABORATORY, for the PHENIX Collaboration)
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Photon-Hadron Azimuthal Correlation Measurement in 200GeV d+Au Collisions at RHIC 2hDeuteron-gold collisions are essential to measure the cold nuclear matter effects, as well as help to interpret the heavy ion collision results to study the quark gluon plasma. Direct photons are less affected by the nuclear medium, thus, they can be used to infer the momentum of the scattered partons. Also, because of the prevalence of the Compton scattering in the direct photon events, the away-side jets are predominantly produced by quark jets. We analyze the azimuthal correlation between high pT direct photons and hadrons and look for the modification of the away-side jet portion of this correlation. The current status of this gamma-jet correlation analysis in d+Au collisions is presented in this poster. This includes analysis of the $x_{E}$ distribution which is related to the fragmentation function D(z). We will also present the status of a new analysis in d+Au of the asymmetry between positive and negative charged hadrons in the away-side quark jets due to the cross-section dominance of up vs down quarks, which can be compared to Au+Au.Speaker: Bing Xia (O)
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Photoproduction of heavy vector mesons in ultra-peripheral PbPb collisions at center-of-mass energy of 2.76 TeV in CMS 2hUltra-peripheral collisions (UPCs) of heavy ions involve long range electromagnetic interactions at impact parameters larger than twice the nuclear radius. At TeV energies, the strong electromagnetic field due to the coherent action of the Z=82 proton charges generates a large flux of photons, which can be used for high-energy photoproduction studies. Heavy vector mesons (for example J/psi, Psi', Upsilon) produced in electromagnetic interactions provide direct information on the parton distribution functions in the nucleus at very low values of Bjorken-x. These events are characterized by a very low hadron multiplicity. The wide pseudorapidity coverage of the CMS detectors is used to separate such events from very peripheral nuclear interactions. The CMS experiment has excellent capabilities for the measurement of the heavy vector mesons in the di-muon decay channel using the tracker and the muon chambers. This analysis is based on the full 2011 PbPb data set of 150/ub. Ultra-peripheral events where one nucleus breaks up are tagged by forward neutrons detected in the Zero Degree Calorimeters. In this talk ratios of Psi' to J/psi, and the yields of J/psi and Psi' per UPC event with nuclear breakup will be presented and compared to theoretical predictions.Speaker: Pat Kenny (University of Kansas (US))
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Pion-Kaon Femtoscopy at $\sqrt{s_{NN}}$ = 200 GeV collisions in STAR at RHIC 2hCorrelations between non-identical particles at low relative momentum in the center of mass ($|\vec{k}^*|$) encode unique information on the space-time structure of the emitting system. In addition to size of the homogeneity region, analysis of correlation functions in the three- dimensional $\vec{k}^*$ space can reveal a space-time offset of one particle species (e.g. kaons) with respect to another (e.g. pions). Early results from STAR at $\sqrt{s_{NN}}$ = 130 GeV showed such an asymmetry, which was consistent with collective radial flow. This early analysis was hampered by the limited particle identification capabilities of the STAR Time Projection Chamber, as well as from marginal statistics and photon conversion due to a significant material budget close to the beam. In year 2010 and year 2011, STAR had accumulated more than one billion minimum bias events at $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions with full Time of Flight detector in operation, which enables detailed non-identical femtoscopy measurements. We present new measurements of pion-kaon correlations in the more sensitive spherical harmonic decomposition representation at $\sqrt{s_{NN}}$ = 200 GeV collisions from these data sets with a lower material budget and much higher statistics. The analysis greatly benefits when information from the STAR Time of Flight detector is used to extend particle identification capabilities. Centrality dependence of pion-kaon femtoscopy in Au+Au collisions will be presented for the first time. Finally, we present a first similar analysis of p+p collisions at $\sqrt{s}$ = 200 GeV.Speaker: Mr Yan Yang (Ohio State University)
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Probing the Initial State with Coherent Vector Meson Scattering in STAR Ultraperipheral Au-Au Collisions 2hUltraperipheral collision events are effectively photoproduction on nuclear targets. These events provide an ideal proving ground for new programs in e+A physics. For the first time, STAR has collected a large enough sample of rho mesons to study their diffractive interaction with Au nuclear targets in detail. The transverse momentum distribution of rho mesons is sensitive not only to the distribution of nucleons in the target, but the dominance of Pomeron exchange at RHIC energies makes this distribution sensitive to the gluon distribution in nuclei. We will describe our latest work on diffractive scattering of rho mesons on Au nuclei and its comparison to several calculations based on different gluon exchange mechanisms. We will also present recent results of the measurement of J/ψ photoproduction in 200 (GeV) AuAu collisions at RHIC. The pT distribution of the J/ψ mesons peaks at very low pT , consistent with expectations for coherent photoproduction. Both the photoproduction cross section and the J/ψ rapidity distribution are expected to show the effects of gluon shadowing. We will present a measurement of the ratio of J/ψ to rho meson cross sections in 200 GeV AuAu collisions, as well as a distribution of J/ψ rapidity within | y |< 1. The measured results will be compared to theoretical models.Speaker: Dr Dilan Madagodahettige Don (STAR (Creighton University))
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Productions of heavy flavor quarks in p+p collisions in PHENIX 2hHeavy flavor quarks such as charm and bottom, provide important probes of the parton energy loss mechanism in quark-gluon plasma. By studying the single electrons coming from the single leptonic decays of D and B mesons, we can study the energy loss of charm and bottom. In order to study the heavy flavor energy loss process, a baseline comparison in p+p collisions where there is no quark-gluon plasma presented is crucial. The Silicon Vertex Detector (VTX) is the latest upgrade installed in PHENIX in 2011, which greatly enhances the ability of the heavy flavor measurement, and will be able to distinguish the production of single electrons produced from charm and bottom decays. The status of the analysis of heavy flavor electrons produced in p+p collisions from 2012 dataset will be presented.Speaker: Dr Chin-Hao Chen (PHENIX Collaboration)
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Propagating fluctuations in fluid dynamic fields 2hWe formulate the propagation of fluid dynamic fields as a propagation of small perturbations around smooth average fluid fields. Fluid dynamic simulations of smooth average initial conditions are then shown to be sufficient to map out the large space of fluid dynamic event histories resulting from arbitrary small fluctuations around these smooth initial conditions. We argue that this provides an efficient way for organizing event-by-event fluid dynamic simulations of heavy ion collisions, and we present details and applications of the approach. Based on: Stefan Florchinger and U.A. Wiedemann, work in preparation and JHEP 1111 (2011) 100Speaker: Urs Wiedemann (CERN)
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Prospects of Low-Mass Dielectron Measurement in ALICE with an upgraded ITS 2hThe measurement of electron-positron pairs in the low invariant mass region allows to study the vacuum and in-medium properties of light vector mesons. Dielectrons also probe the production of thermal photons in heavy-ion collisions. ALICE is well-suited to perform this measurement due to its excellent tracking and particle identification capabilities at very low momenta. However, Dalitz decays and photon conversions lead to a high combinatorial background. Additionally, coincident semi-leptonic decays of charm and anti-charm hadrons produce a continuum signal, which dominates over a thermal dielectron signal. Both contributions can be reduced by an improved Inner Tracking System, to be installed during LHC's long shutdown (2018). It will further improve the tracking efficiency at low p_t and provide excellent detection capabilities for electrons from secondary vertices like conversions and heavy-quark decays. The expected impact of a new ITS on the low-mass dielectron measurement in pp and Pb-Pb collisions will be presented. To further increase the acceptance for low p_t tracks, a reduction of the magnetic field in the ALICE central barrel from 0.5 T to 0.2 T is considered. Its influence on the low-mass dielectron measurement will be discussed.Speaker: Patrick Simon Reichelt (Johann-Wolfgang-Goethe Univ. (DE))
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QGP shear viscosity from combined analysis of elliptic and triangular flow 2hThe Quark-Gluon Plasma (QGP) created in heavy-ion collisions is well described by viscous hydrodynamic simulations. A key QGP transport coefficient, its specific shear viscosity eta/s, can be extracted by comparing such simulations with experimental data. Previous extractions gave (eta/s)_QGP ~ (1-2.5)/(4\pi) where the ~100% uncertainty arises mainly from ambiguities in the initial fireball shape and density profile. To obtain (eta/s)_QGP with better precision, the ambiguities in the initial conditions must be addressed. Published extractions of the specific shear viscosity have relied on elliptic flow measurements and the fact that eta/s suppresses elliptic flow. It was recently realized that higher order harmonic flows are suppressed even more strongly with increasing eta/s, and that the recently measured triangular flow allows to simultaneously constrain eta/s and the initial conditions: viable initial conditions should describe the elliptic and triangular flows v2 and v3 simultaneously with the same eta/s. We have performed such a simultaneous analysis of v2 and v3 [1]. We show that the normalized elliptic and triangular flow coefficients v2/ecc2 and v3/ecc3 (where ecc_n are the n-th order eccentricities of the initial state) can be obtained with 10-15% accuracy using single-shot hydrodynamical simulations where the initial conditions are averaged before hydrodynamical evolution, instead of the more realistic but costly event-by-event hydrodynamical approach where averaging is done only after separate evolution of each fluctuating initial condition. For elliptic flow we find that, within 10-15%, v2/ecc2 = v2{2}/ecc2{2} = v2{4}/ecc2{4} where the expression on the left is obtained from single-shot hydrodynamics while the cumulant expressions on the right are extracted from event-by-event hydrodynamics. For triangular flow we find, at the same level of precision, that v3/ecc3=v3{2}/ecc3{2} \neq v3{4}/ecc3{4}. The ALICE data for charged hadron elliptic and triangular flow from Pb-Pb collisions at the LHC [2] are shown to obey these approximate (in-)equalities. Our hydrodynamic analysis [1] shows that the ALICE v2 and v3 data [2] can be explained simultaneously, at all collision centralities, if (eta/s)_QGP \approx 1/(4\pi). This requires MC-Glauber initial conditions which have smaller ecc2 than CGC-motivated MC-KLN initial conditions. For MC-KLN initial conditions the v2 data require larger (eta/s)_QGP ~ (2-2.5)/(4\pi) which, however, then underpredicts the measured triangular flow by 35-40%. We conclude that the large v3 measured at the LHC requires either almost minimal QGP shear viscosity (eta/s)_QGP \approx 1/(4\pi), or a presently unknown mechanism for increasing the triangularity fluctuations in the initial state by ~50%. [1] Zhi Qiu, Chun Shen, and Ulrich Heinz, ``Hydrodynamic elliptic and triangular flow in Pb-Pb collisions at sqrt(s)=2.76 A TeV,'' Phys. Lett. B707, 151-155 (2012). [2] K. Aamodt et al. (ALICE Coll.), ``Higher harmonic anisotropic flow of charged particles in Pb-Pb collisions at sqrt(s_NN)=2.76 TeV," Phys. Rev. Lett. 107, 032301 (2011).Speaker: Dr Zhi Qiu (Ohio State University)
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Quantum Description of Impurities - Heavy Quarks and Quarkonia 2hSingle heavy quark system has been considered as a hard probe for dynamical information of quark-gluon plasma (QGP), namely drag force, while heavy quarkonium has been thought to probe static information, such as heavy quark potential. However, this intuitive picture is not correct, in particular for the latter. Recent theoretical developments have shown that dynamical feature is also important in the physics of heavy quarkonia through complex heavy quark potential [1]. This complex potential can be understood as stochastic process in the medium [2]. However, as pointed out in [2], complete description must also explain the irreversible process, which results in drag force in the classical limit. In other words, a unified description of heavy quark systems is required. In this presentation, I will develop such a quantum description for heavy quark systems in QGP on the basis of closed-time formalism in non-equilibrium field theory. In this description, I will explain how we can obtain the stochastic process and the drag force from the first principle and derive the master equation for quantum evolution of the heavy quark systems. [1] M. Laine et al., JHEP 0703 (2007) 054; JHEP 0705, 028(2007). A. Beraudo, J. P. Blaizot and C. Ratti, Nucl. Phys. A806, 312 (2008). N. Brambilla, J. Ghiglieri, A. Vairo and P. Petreczky, Phys. Rev. D 78, 014017 (2008). A. Rothkopf, T. Hatsuda and S. Sasaki, arXiv:1108.1579 [hep-lat]. [2] Y. Akamatsu and A.Rothkopf, arXiv:1110.1203 [hep-ph] (to be published in PRD).Speaker: Yukinao Akamatsu (Nagoya University)
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Quark pair productions in pA collisions from CGC with running coupling BK evolution 2hWe study the parton saturation effects on heavy quark production in proton-nucleus collisions at collider energies, using the CGC formula proposed by Blaizot-Gelis-Venugopalan (Nucl.Phys.A743:57-91,2004). Previously it was numerically evaluated using the unintegrated gluon distribution from the McLerran-Venugopalan model including the x-evolution effect with the Balitsky-Kovchegov equation (Fujii-Gelis-Venugopalan, Nucl.Phys.A780:146-174,2006). Here we extend the phenomenological study by including the running coupling effect in the x-evolution. We will investivate the saturation effects on the quark and quark pair spectra, and the quarkonium spectrum as well, at the RHIC and LHC energies.Speaker: Kazuhiro Watanabe (The University of Tokyo)
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Quark-gluon plasma shear viscosity at RHIC and the LHC: results from the hybrid model VISHNU 2hViscous hydrodynamic calculations have shown that the quark-gluon plasma (QGP) shear viscosity can be extracted from elliptic and triangular flow data [1]. However, strong non-equilibrium effects, both in the chemical composition and the kinetic evolution, during the hadronic stage influence the development and distribution of flow anisotropy and must be correctly accounted for when extracting the QGP viscosity. For an improved description of the hadronic evolution, we developed the hybrid model VISHNU which couples viscous hydrodynamic expansion of a QGP fluid to a microscopic description of hadronic rescattering and chemical and thermal freeze-out using the UrQMD cascade [2]. In this talk, we will summarize a number of key results obtained with VISHNU: a) We present a robust method for extracting the QGP viscosity from the collision centrality dependence of the eccentricity-scaled charged hadron elliptic flow [3]. b) We extract the QGP shear viscosity at RHIC energies from elliptic flow data, giving quantitative estimates for and initial pre-equilibrium flow and from model ambiguities of the initial fireball eccentricity. We discuss the prospects for reducing the main uncertainties from initial conditions through a combined analysis of elliptic, triangular and higher-order harmonic flow coefficients using event-by-event VISHNU simulations. c) We show that, with the QGP viscosity extracted in [3], VISHNU yields an excellent description of all soft-hadron data from Au+Au collisions at top RHIC energy [4]. d) Extrapolating to Pb+Pb collisions at the LHC, and comparing with recent experimental results from the ALICE Collaboration, we show that the LHC data are again well described by VISHNU, with approximately the same constant QGP viscosity as at RHIC energies [5], including the proton elliptic flow in the most central collisions which cannot be correctly reproduced in a purely hydrodynamic approach [6]. e) Using an improved implementation of baryon-antibaryon annihilation in UrQMD, VISHNU is shown to resolve the ``proton puzzle" at the LHC [7]. References [1]H. Song and U. Heinz, Phys. Lett. B 658, 279 (2008); Phys. Rev. C77, 064901 (2008), Z. Qiu, C. Shen and U. Heinz, Phys. Lett. B 707, 151 (2012). [2]H. Song, S. Bass and U. Heinz, Phys. Rev. C83, 024912 (2011). [3]H. Song, S. Bass, U. Heinz, T. Hirano and C. Shen, Phys. Rev. Lett. 106, 192301 (2011). [4]H. Song, S. Bass, U. Heinz, T. Hirano and C. Shen, Phys. Rev. C83, 054910 (2011). [5]H. Song, S. Bass and U. Heinz, Phys. Rev. C83, 054912 (2011); U.Heinz, C. Shen and H. Song, arXiv:1108.5323 [nucl-th]. [6]C. Shen, U. Heinz, P. Huovinen and H. Song, Phys. Rev. C84, 044903 (2011). [7] H. Song, S. Bass and U. Heinz, in preparation.Speaker: Huichao Song (The Ohio State University)
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Quarkonium measurements with the proposed sPHENIX detector 2hThe PHENIX collaboration is in the process of developing an ambitious upgrade plan (called sPHENIX) to significantly improve physics capabilities and make use of the full enhanced luminosity at RHIC. The sPHENIX design contains silicon tracking, electromagnetic and hadronic calorimetry with large kinematic coverage and high data rate capabilities to sample 50 billion Au+Au collisions annually. This poster will describe how additional tracking layers and a preshower detector, will enable us to measure and resolve the three bottomonium Y(1S), Y(2S) and Y(3S) states decaying into di-electrons. Expected mass resolution, signal to background ratios for various assumptions of pion rejection factors will be presented.Speaker: Marzia Rosati (Iowa State University)
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Realistic medium-averaging in GLV radiative energy loss 2hThere has been a lot of interest in testing radiative energy loss calculations against data from RHIC and the LHC. It is customary, as in the Gyulassy-Levai-Vitev (GLV) approach, to formulate the energy loss of a jet parton as a line integral from the production point along a straight-line trajectory. Calculations then account for variations in path length with jet origin and direction, and most recently also for fluctuations in the medium density (lumpiness), which give rise to fluctuations in energy loss that significantly affect high-pT observables such as the nuclear suppression R_AA or the momentum anisotropies v_n. These studies, however, ignore that the line integrals themselves represent an average over the location of possible interaction points (color sources in GLV) along the jet path. We will present results from a calculation with stochastically chosen interaction points for each jet, which gives additional fluctuations in energy loss. The influence of these fluctuations on RHIC and LHC observables will be discussed utilizing both medium density parameterizations and realistic medium evolution from bulk dynamics models, such as the parton transport MPC. A special advantage of using parton transport is that it conveniently provides the evolution of an ensemble of scattering centers.Speaker: Mr Deke Sun (Purdue University)
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REGGAE: Monte Carlo generator of momenta obeying energy and momentum conservation 2hA Monte Carlo event generator REGGAE is presented which can generate momenta for given set of particles so that total energy and momentum assumes a pre-set value. The generator is proved to fill the available phase-space uniformly. In comparison to other algorithms it is considerably more effective in situations where many particles are produced and/or large part of the total energy is stored in form of the masses of particles.Speaker: Boris Tomasik (Univerzita Mateja Bela (SK))
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Relation Between the Trace Anomaly and Shear Viscosity in Clustering of Color Sources and the Equation of State of the QGP 2hThe major challenge in heavy ion physics is to extract the equation of state and the shear viscosity to entropy ratio $\eta/s$ from the data. In the clustering of color sources (CSPM) the charged particle transverse momentum spectrum is used to measure the percolation density parameter $\xi$, which determines the initial temperature T, energy density $\epsilon$, and the $\eta/s$ ratio versus T in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV . For 0.9 $T_{c} < T < $1.2 $T_{c}$ ($T_{c}$ = 167.7 MeV), the sound velocity $C_{s}^{2}$ from the mass less non interacting constituent version of CSPM agrees with Lattice QCD (LQCD)$C_{s}^{2}$ values . For T$ >$ 1.2$T_{c}$ there is a significant difference with the LQCD values\cite{eos}. The measured CSPM value for $\eta/s$ = 0.20, at 1.15$T_{c}$ is consistent with a strongly coupled QGP and increases with T. The Trace Anomaly $\triangle $ is defined as $(\epsilon-3p)/T^{4}$. Above $T_{c}$, the LQCD $\triangle $ and the reciprocal of $\eta/s$ fall off with 1/T. At $T_{c}$ , $s/\eta$ has a magnitude of $\sim$5.5 , non interacting - CSPM has a $\triangle\sim$ 5.5 and LQCD $\triangle \sim $5.5. The change in $\triangle$ and $s/\eta$ with 1/T describes the transition from a strongly to weakly coupled QGP. Above $T_{c}$, $s/\eta$ and the LQCD $\triangle$ may have the same underlying structure. The $C_{s}^{2}$ values for the QGP obtained using the $s/\eta \sim 5.5$ version of CSPM above $T_{c}$ are in excellent agreement with LQCD \cite{wupp, hotqcd}. The CSPM predictions for Pb-Pb and p-p collisions at LHC energies will be presented.Speaker: Prof. Rolf Scharenberg (Purdue University)
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Relativistic Fluctuating Hydrodynamics and its Application to Heavy Ion Collisions 2hTo investigate the physics of the strongly interacting system of quarks and gluons under extreme conditions, heavy-ion collision experiments are performed at Large Hadron Collider (LHC) and Relativistic Heavy Ion Collider (RHIC). One of the major discoveries was that elliptic flow v_2 was comparable with an ideal hydrodynamic prediction and, as a result, that a new paradigm of strongly coupled quark-gluon plasma (QGP) was established. Recently, the higher harmonics v_n (n > 2) are systematically observed at RHIC and LHC and attract a lot of theoretical and experimental interests. Initial state fluctuations turned out to be important to explain these higher harmonics. In addition to initial state fluctuations, thermal fluctuation during the space-time evolution of the QGP also plays an important role in event-by-event simulations. We first formulate the relativistic fluctuating hydrodynamics in the context of the second order causal theory. Finite relaxation time for dissipative current is required to make hydrodynamic equation consistent with causality. Instead of introducing the relaxation term itself, one can define a kernel function (or a retarded Green function) such that constitutive equation becomes convolution of the kernel function including relaxation as well as dissipation and the corresponding thermodynamic force. One can also introduce a noise field as thermal fluctuation of the dissipative current like in the Langevin equation. Thus the constitutive equation becomes no longer a deterministic equation, but a stochastic equation. The power spectrum of the noise fields is intimately related to the kernel function via the fluctuation-dissipation relation and, consequently, noise becomes colored noise rather than white one due to the finite relaxation time. We then implement the colored noise together with viscous kernels in numerical simulations of relativistic hydrodynamics and perform simulations on an event-by-event basis to see effects of thermal fluctuation on the dynamics of heavy ion collisions. This framework is beyond the conventional second order dissipative hydrodynamics and, thus, will become important in the upcoming era of the precision QGP physics by means of high-energy heavy ion collisions.Speaker: Koichi Murase (The University of Tokyo)
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Relics of Quark Hadron Phase Transition in the Microsecond Universe with a “little inflation” 2hThe conventional scenario to date of the quark hadron phase transition in the microsecond old universe is essentially guided by lattice calculation leading to a cross over from quarks to hadrons. However, it is entirely possible that Affleck – Dine mechanism of baryogenesis leading to a large baryon asymmetry is more natural than in other models along the route baryogenesis via leptogenesis. In this model [1] the universe is assumed to begin with a large baryon chemical potential through an Affleck – Dine mechanism and then undergoes a “little (or tepid) inflation” after crossing the QCD first-order phase transition line, while remaining in a deconfined and a chirally symmetric phase. We exploit first order phase transition [2] and examine critically what could be the relics. Candidates such as “Strange Quark Nuggets” (SQN), even Dark energy and floating “orphan” quarks are going to be discussed. [1] T. Boeckel and J. Schaffner – Bielich Phys. Rev. Letts 105, 041301 (2010). [2] P. Bhattacharya, J. Alam, S. Raha and B. Sinha, Phys. Rev. D 48, 4630 (1993) A. Bhattacharya, J. Alam. S. Sarkar, P. Roy, B. Sinha, S. Raha and P. Bhattacharya, Phys. Rev. D 61, 093509 (2000)Speaker: Bikash Sinha
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Response of QGP to two hard partons 2hWe perform (3+1)-dimensional ideal hydrodynamic calculation with source terms that describe energy and momentum deposition of hard partons in static quark-gluon plasma and study not only QGP response to one parton, but also interplay of perturbations due to two leading particles propagating in various directions. Energy deposition is described by a simple Bethe-Bloch model which leads to an explosive burst of energy and momentum at the end of the trajectory of the parton. Dependence of the response on the equation of state is also discussed. The pairs of hard partons induce flow of energy and momentum density in medium which depend on initial directions of the partons.Speaker: Martin Schulc (Czech Technical University (CZ))
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Results from Fixed-Target Collisions from STAR: Au+Al at $\root{S_{NN}}$ = 4.5, 3.5 and 3.0 GeV 2hThe RHIC Beam Energy Scan (BES) was proposed to search for the possible critical point and to study the nature of the phase transition between hadronic and partonic matter. However, several dynamical model simulations (UrQMD, PHSD, QGSM, GiBUU, 3-fluid) suggest that the partonic phase is entered for center-of-mass collision energies as low as 4-5 GeV [1]. Collisions between beam halo nuclei and the aluminum beam pipe allow STAR to study fixed-target Au+Al collisions. The injection and sub-injection energy gold beams (kinetic energies of 8.8, 4.8 and 2.9 AGeV) produce Au+Al collisions at center-of-mass energies of 4.5, 3.5, and 3.0 GeV. Particle ratios will be presented and compared to earlier published results from the AGS, SPS,and RHIC. Fixed target acceptances and efficiencies for tracking in the TPC and particle identification in the Time of Flight system will be discussed. References: [1] I.C. Arsene et al., Phys. Rev. C75, 034902 (2007).Speaker: Brooke Haag (U)
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Role of chaoticity and information entropy in Multiparticle production at collider experiments 2hRecent data from LHC has revived the question whether the matter produced in high energy hadronic collisions is thermalized or not. With the published data from ALICE and CMS experiments, we have shown that the multi-particle production in p+p collisions at LHC energies available up to now, follows the scaling of information entropy if one takes the chaotic and coherent sources of particle production into account and the information entropy is extracted from the chaotically produced particles. Based on these scaling properties we have argued that in hadronic collisions at the highest energies projected for LHC, almost all the particles will be produced chaotically. This indicates that a collective behavior will be observed even in the hadron-hadron collisions at that energy. Further connections of this study with heavy ion interactions will be elucidated.Speaker: Dr Supriya Das (Bose Institute)
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Scaling of high momentum harmonics: constraining energy loss models, and looking for opacity changes 2hIn this talk we show that azimuthal harmonics of hard particles, thought to be generated via parton energy loss, should scale differently w.r.t. multiplicity and system size to azimuthal harmonics of soft particles, thought to be generated by hydrodynamic response. By scanning harmonics in both energy and system size, we obtain a way of determining the domain of validity of the "hydrodynamic" vs. the "tomographic" regime at different energies. Such scaling studies would further help to isolate the energy-loss regime relevant for RHIC and LHC energies (Bethe-Heitler, LPM, AdS/CFT) and to isolate changes in the intensive properties of the system, such as opacity and entropy density, using "hard" observables. In particular, a scaling breaking could be instrumental in finding changes in such intensive quantities, and would provide a direct link between jet suppression and the onset of partonic degrees of freedom. Based on ongoing work with the model described in http://arxiv.org/abs/1102.5416Speaker: Giorgio Torrieri (JW Goethe Universitat, Frankfurt)
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Search for critical fluctuations in the proton transverse momenta for A+A collisions at the NA49 experiment (SPS, CERN) 2hWe perform factorial moment analysis in the transverse momentum space of protons produced at midrapidity in A+A collisions at the NA49 experiment (SPS, CERN). After background subtraction we find power-law dependence of the correlator on the number of phase space cells for the systems Si+Si and Pb+Pb at 158A GeV with large values of the associated characteristic exponent (intermittency index). This behaviour is expected to occur when approaching the chiral critical endpoint of hadronic matter. Especially for the Si+Si system the measured intermittency index approaches in size the predictions of critical QCD. The intermittency effect is suppressed in Pb+Pb collisions at 40A GeV. The results of our analysis indicate that the value of the critical baryochemical potential should be closer to 240 MeV than to 380 MeV.Speakers: Prof. Fotis Diakonos (University of Athens, Physics Department, Section of Nuclear and Elementary Particle Physics, GR-15771), Nikolaos Davis (University of Athens (GR))
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SHARE with CHARM describes PbPb hadron yields at 2.76 TeV 2hSoft hadron production at LHC energies presented a new challenge for the statistical hadronization mode (SHM). We show that the SHARE chemical nonequilibrium model describes well the available hadron yield data. We than extend SHARE to include CHARM contribution to hadron yields and present a remarkably accurate description of hadron yields at energy s_{NN} =2.76 TeV for several high multiplicity centrality bins.We show that ignoring the charm contribution can introduce up to 40% contribution in yields of certain hadrons which, when measured, offer an indirect evaluation of charm production yield. We demonstrate that employing SHARE with CHARM our current fit of pions, kaons, protons, Xi's and Omegas is fully consistent with our understanding of AuAu and CuCu data at 62.4 and 200 GeV. This demonstrates the overall superiority of the chemical nonequilibrium SHM model in predicting hadron production in relativistic heavy ion collisions.Speaker: Michal Petran (Czech Technical University (CZ))
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Shear Viscosities of Hadronic Gases 2hWe present a detailed comparison between two different methods to calculate the shear viscosity coefficient for a set of four hadronic systems. One calculation employs the Chapman-Enskog method to calculate the shear viscosity coefficient for a hot hadronic system. The other calculation uses the Green-Kubo method to calculate the shear viscosity for a hadronic medium simulated using the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model. The calculations are performed over a temperature range of 60-200 MeV, and the differences in the values for the calculations are highlighted. The degrees of freedom and cross sections of the systems for the two calculations are synchronized to ensure the most accurate comparison possible. The systems studied include those of massive and massless pions with a fixed cross section, that of chiral pions with energy dependent cross section, and that of a gas of pions and rho resonanaces. The lifetime of the rho resonance is varied and the effect of the rho resonance lifetime on the shear viscosity is investigated.Speaker: Dr Nasser Demir (Kuwait University)
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Shear Viscosity in NJL-type Models 2hCollision experiments with heavy ions at RHIC and CERN help to explore the nature of the deconfined quark-gluon phase. The matter created in such collisions behaves as an almost-perfect fluid indicated by very small dissipative effects. We use the two-flavor NJL model to approximate the QCD physics at high temperatures $T\gtrsim 200\,\text{MeV}$. A large-$N_c$ expansion is applied to include mesonic fluctuations in the fundamental quark sector. We discuss the impact of this expansion to the gap equation and the dynamics leading to a finite shear viscosity of the quarks.Speaker: Robert Lang (TUM)
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Signature of liquid-gas phase transition and critical behavior in projectile multifragmentation 2hA high-statistics exclusive study of the multifragmentation of Mg-Em interaction at 4.5 AGeV has been performed to realize the critical behaviour. A number of relevant observables such as fluctuation in the sizes of the largest cluster, reduced variance and the mean value of second moment of charge distribution were estimated with the experimental data. The observed results are compared with the results of Kr-Em interaction at 0.95 AGeV as well as the results of EOS collaboration for Au, La and Kr on carbon at 1 AGeV. Systematic variation in the heights and positions of the peaks observed with the change of the fragmenting nuclei thereby confirms the critical behaviour and a possible association of liquid-gas phase transition on multifragmentation mechanism.Speaker: Ms Rupalim Talukdar (Department of Physics, Gauhati University, India)
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Silicon pixel and strip detector development for the upgrade of the ALICE Inner Tracking System 2hThe main physics motivation for the upgrade of the Inner Tracking System of the ALICE experiment is to perform new measurements on charm and beauty production in heavy-ion collisions, dealing with the challenge of expected Pb-Pb interaction rates of up to 50 kHz. For this purpose, a new silicon tracker is needed with greatly improved features in terms of determination of the distance of closest approach to the primary vertex, standalone tracking efficiency at low transverse momentum, momentum resolution and readout rate capabilities. The ITS upgrade foresees to replace the present ITS detector with a new seven layer silicon vertex detector. Two layouts are being considered: Layout 1 foresees to equip all layers with monolithic silicon pixel detectors; Layout 2 will consist of 3 layers of hybrid silicon pixel detectors and 4 layers of double-sided silicon strip detectors. For the innermost layers, there is a strong effort to decrease the pixel dimensions to about 20-30 um in the bending direction and equivalently in the beam direction and to reduce the material budget from 1.1% to 0.3% of X0, by using monolithic pixel detectors or hybrid pixel detectors with thinned chip and sensor, and minimizing the contribution coming from supports and services. The different types of monolithic pixel detectors under consideration for the ALICE ITS upgrade are: the rolling shutter, low power, architecture of the MIMOSA26 and ULTIMATE sensors, moved to a 0.18 um technology node; the INMAPS prototype, an in-pixel hit discrimination CMOS sensor based on a deep p-well extension of a triple-well 0.18 um CMOS; the LePIX development, a drift-based monolithic sensor in very deep submicron CMOS. The expected radiation levels for the innermost layer (685 krad TID, 10^13 neq per year) will require a careful validation of the different technologies in terms of radiation resistance. On the outermost layers the needed granularity and pointing resolution can be ensured by a strip detector geometry with a small cell size (95 um strip pitch, 22 mm strip length) and a small strip inclination with respect to the beam direction. The information on the signal amplitude will be preserved for the strip sensors for particle identification purposes. The strip readout chip will incorporate a low power ADC with 10 bits resolution. The present status of the technology development for the considered options will be reported.Speaker: Giacomo Contin (Universita e INFN (IT))
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Simulation of hadronic cocktail decay contributions to the dielectron spectrum within the PHENIX acceptance 2hDielectron spectra in Au+Au collisions carry important information on the properties of the hot dense matter created in the early stage of the collisions. The earlier PHENIX measurement, using data taken in 2004 shows significant deviations from hadronic decay expectations. The most recent data set from 2010, taken with the the Hadron Blind Detector (HBD) upgrade designed to reduce the combinatorial background, promises to be a more significant result. This new data set requires an update to the simulations of hadronic cocktail contributions. The cocktail provides the benchmark for studying medium effects, such as the previously reported low mass excess. The new simulation takes into account improved PHENIX measurements of the cross sections for some of the hadrons (\eta, \phi, \omega), as well as an improved line shape of the \rho meson. In addition, it also includes the modified PHENIX acceptance and additional detector material. Results on the new cocktail and comparison with dielectron spectra will be shown.Speaker: Jiayin Sun (Stony Brook University)
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Single electrons from heavy flavor decays in 200 GeV Cu+Cu collisions at PHENIX 2hSince heavy flavor quarks are produced early in the collision, they experience the full evolution of the medium and are thus a good probe of medium effects. Electrons from open heavy flavor have previously been measured for p+p, Au+Au and d+Au collisions at the Relativistic Heavy Ion Collider (RHIC) by PHENIX. In the most central Au+Au the yield is suppressed relative to a Ncoll scaled p+p which suggests that the heavy quarks lose a significant portion of their initial energy in the medium. A similar analysis done in the d+Au collisions suggests that there are cold nuclear matter effects that are masked by the hot, dense medium produced in the Au+Au collisions. New results from Cu+Cu collisions provide an important look at the Ncoll region between the d+Au and Au+Au systems. The Cu+Cu results will be shown for different centralities along with a comparison to the d+Au and Au+Au results. The nuclear modification factor, RAA, will also be shown as a function of Ncoll, giving a more complete picture as the cold nuclear matter effects in d+Au collisions are taken over by the effects of the hot medium in the Au+Au system.Speaker: Nicole Apadula
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Soft gluon emission and energy loss of heavy flavors in relativistic heavy ion collisions 2hMost of the the calculations on gluon emission off a heavy quark, within perturbative QCD, have been performed in the literature using light cone gauge with eikonal approximations. Recently we revisited the issue in Feynman gauge that resulted in a very compact and elegant expression for the suppression factor for gluon emission off a heavy quark [1]. This generalization is valid for the full range of rapidity of the radiated gluons and also has no restriction on the scaled mass of the quark with its energy. In the appropriate limit it correctly reproduces the usual dead cone factor in the forward rapidity region [2]. On the other hand, this suppression factor becomes close to unity in the backward direction. We then obtain the radiative energy loss of a heavy quark in a deconfined medium due to radiation of gluons off them using this derived gluon emission spectrum. We find that the heavy flavor loses energy almost in a similar fashion like light quarks through this process. This indicates a small suppression of gluon emission in the backward region, which should have an impact on the phenomenology of heavy quark energy loss in the hot and dense matter produced in ultra-relativistic heavy-ion collisions. An analysis of the nuclear modification factor for $D$-meson at LHC is found to be in very good agreement with the most recent data from ALICE collaboration at 2.76 ATeV Pb-Pb collisions [3]. 1. R. Abir, C. Greiner, M. Martinez, M. G. Mustafa and J. Uphoff, "Soft gluon emission off a heavy quark revisited" Phys. Rev. D 85, 054012 (2012) arXiv:1109.5539 [hep-ph]. 2. Y. L. Dokshitzer and D. E. Kharzeev "Heavy quark colorimetry of QCD Matter" Phys. Lett. B 519 (2001) 199-206 3. R. Abir, U. Jamil, M. G. Mustafa and D. K. Srivastava, "Heavy Quark Energy Loss and D Mesons at LHC" arXiv:1203.5221 [hep-ph].Speaker: Mr Raktim Abir (Saha Institute of Nuclear Physics)
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Source chaoticity in heavy-ion collisions at the LHC 2hQuantum coherence is fundamental in the interpretation of geometrical information from HBT measurements. The effect of quantum coherence is not only to lower the correlation strength of HBT correlations but also to modify the shape. We present measurements of the source chaoticity from Pb+Pb sqrt(s) = 2.76 TeV collisions at the LHC using the ALICE detector. Three-pion and two-pion correlations strengths are used together to determine the source chaoticity. The corresponding impact of quantum coherence on the HBT radii will be discussed as well.Speaker: Dhevan Raja Gangadharan (Ohio State University (US))
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Spectra and flow of thermal and non-thermal photons at highest collider energies 2hPhotons, as all electromagnetic probes, can give direct access to the hot and dense phase of a heavy-ion reaction. We show calculations of direct photon emission at highest energies available with the UrQMD-hybrid model. UrQMD is a full microscopic+macroscopic transport/fluiddynamics hybrid model with hadron- and string-driven equilibration phase, a fll (3+1)-dimensional fluiddynamic hot and dense phase and a hadronic after-burner. Unequilibrated matter at high rapidity is preserved during the fluid phase. A strong emphasis is set on the impact of viscosity and Equation of State at zero and non-zero band string aryon density to the spectra and flow patterns of thermal and non-thermal photons in A+A-collisions at RHIC, LHC.Speaker: Björn Bäuchle (FIAS Frankfurt)
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Speed of sound and dynamics of relativistic heavy ion collisions 2hCollective flow is an essential component in describing the dynamics of relativistic heavy ion collisions. The flow characteristics are intimately related to the equation of state of the thermally equilibrated matter created in these collisions through the speed of sound. Using either the Bjorken or Landau hydrodynamics or a combination thereof it is possible to relate the particle yields to the speed of sound. Here we study the flow properties using the equation of state from an effective model and discuss the possible distinctive signatures at low densities and high temperature relevant for LHC and at high densities and low temperatures relevant for FAIR. The difference in characteristics of these two scenarios may help us in identifying the region around the critical end point.Speaker: Prof. Sanjay Ghosh (Bose Institute)
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sPHENIX Jet Reconstruction Performance 2hReconstructed jets in heavy ion collisions are a crucial tool for understanding the quark-gluon plasma. The separation of jets from the underlying event is necessary, particularly in central heavy ion collisions, in order to quantify medium modifications of the parton shower. Here, we describe a method for quantifying the underlying event contributions in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV utilizing the HIJING event generator (from arXiv:1203.1353) and show the expected jet reconstruction performance in heavy ion collisions using the proposed sPHENIX upgrade dector.Speaker: Anne Sickles (Brookhaven)
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sPHENIX Jet Upgrade Program: Unraveling Strong versus Weak Coupling 2hThe PHENIX Experiment is proposing an exciting suite of upgrades called sPHENIX, with a first stage including a world class jet detector with full electromagnetic and hadronic calorimetry capable of sampling up to 50 billion Au+Au collisions annually and measuring jets over a broad kinematic range and with high statistics (over 10 million jets above 20 GeV and over 100,000 jets above 40 GeV). The motivation for extending the jet program of the LHC to temperatures in the range of the transition temperature and varying the scale for probing the medium relates directly to the question of how strong coupling works near the transition temperature and how rapid the approach to weak coupling might be. In this presentation, we detail the various theoretical calculations and how a comprehensive world program (at both RHIC and the LHC) of jet and high energy hadron and photon measurements will be key to unravel this puzzle.Speaker: Prof. Jamie Nagle (University of Colorado)
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STAR measurements of centrality dependence of elliptic flow for identified hadrons in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV 2hElliptic flow $v_2$ is one of the key observables to study the bulk properties at freeze-out as well as hadron production mechanisms in the ultra relativistic heavy ion collisions. It has been observed that number of constituent quark (NCQ) scaling of $v_2$ holds among measured identified hadrons at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV in Au + Au collisions at RHIC. The scaling of $v_2$ strongly indicates that the collectivity develops at the stage where the partonic degrees of freedom are relevant. Studying the NCQ scaling of $v_2$ as a function of transverse momentum $p_T$ and centrality will shed light on the production mechanisms for hadrons in heavy ion collisions. We present the results of $v_2$ as a function of $p_T$ for identified $\pi^{\pm}$, $K^{\pm}$, $K^0_S$, $p$, $\bar{p}$, $\Lambda$ and $\bar{\Lambda}$ in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The NCQ scaling of $v_2$ in several different centrality classes is discussed.Speaker: Dr Hiroshi Masui (LBNL)
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Status of the analysis using the Forward Vertex Detector at PHENIX 2hThe Forward Vertex Detector (FVTX) was installed in PHENIX this year and operated during the $\sqrt{s}=$510 GeV $p$+$p$, $\sqrt{s_{NN}}=$193 GeV U+U, and $\sqrt{s_{NN}}=$200 GeV Cu+Au runs. The FVTX has full azimuthal coverage between 1.2$<|y|<$2.2 and consists of 4 stations with 2 planes of silicon mini-strips with 75 $\mu$m pitch in the radial direction and 96 azimuthal segments. The resolution of the distance of closest approach (DCA) measured by the FVTX is suitable for the identification and separation of charm and bottom quark decay yields. We also expect to improve the measurement of the dimuon opening angle and reduce background, providing J/$\psi$, $\psi^{\prime}$ mass peak separation. This poster will show the status of the analysis of the data collected by the FVTX this year.Speaker: Cesar Luiz da Silva (L)
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Strange Quark Nuggets as Baryonic Dark matter from the Relics of Cosmic QCD Phase transition 2hThe universe is assumed to begin with a large baryonic chemical potential acquired through an Affleck – Dine mechanism, which leads on to a baryon asymmetry of 0(1) without requiring superhigh temperatures. However, the observed baryon asymmetry of 0(10-10) at CMB temperature needs to emerge naturally from such a scenario. This is what could be achieved through a “little inflation” of about 7 e – folding leading to a QCD first order transition [1], while remaining in a deconfined and in a chirally symmetric phase. It was demonstrated [2] using chromoelectric flux-tube fission model that some strange quark “nuggets” (SQN) [3] with an initial baryon number ~ 1044 or more can survive the evaporation process and be stable on cosmological time scales. We demonstrate that these SQN’s are natural candidates for baryonic dark matter. We also argue that these SQNs, together with the natural requirement that the total baryon number of the universe is an integer [4], can explain the occurrence of the cosmological dark energy within the standard model of particle physics. [1] T. Boeckel and J. Schaffner – Bielich, Phys. Rev. Lett. 105, 041301 (2010) [2] P. Bhattacharjee et. al. Phys. Rev. D 48 , 4630 (1993) [3] E. Witten, Phys. Rev. D 30 272 (1984) [4] S. Banerjee et al. Phys. Lett. B611, 27 (2005)Speaker: Bikash Sinha
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Strong Color Fields in Nuclei from Fits to Nuclear Parton Distributions 2hWe consider a modified version of the McLerran-Venugopalan model where the thickness of the nucleus is finite and infrared divergences are removed by the color neutrality condition. The strong coupling constant and the nucleon size are treated as parameters. To determine these parameters, the x-dependent gluon distribution function is calculated at very low momentum, which is the region of validity of this model. The resulting distribution function is evolved with the DGLAP equation to higher momenta by using the QCDNUM package and compared with data as parametrized by nuclear CTEQ. This allows us to infer the parameters, and hence to calculate the classical color fields representing the initial conditions in high energy heavy-ion collisions without any free parameters.Speaker: Sener Ozonder (University of Minnesota)
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Study of $b\bar{b}$ production using correlated like-sign dimuons at PHENIX 2hProduction of open bottom (B) mesons is an important tool to probe the hot and dense matter created from nucleus-nucleus collisions at the Relativistic Heavy Ion Collider (RHIC). In the mass region between 4.5 and 12 GeV, the only source of correlated like-sign dimuons will come from the semileptonic decay of B meson pairs. The number of correlated like-sign dimuons due to neutral B meson oscillation is directly related to the total number of open bottom meson pairs and thus can provide a way of constraining the open bottom contribution to the dimuon continuum in the high mass region. To establish this new analysis method, correlated like-sign dimuons from pairs of B mesons of $\sim$6.3 pb$^{-1}$ data from p+p collisions at $\sqrt{s}$ = 500 GeV within the PHENIX muon arms acceptance (1.2 < |y| < 2.2) were studied. Results from this study will be presented. In the future, this analysis method can be applied to the $\sqrt{s}$ = 200 GeV p+p collisions in order to determine a baseline for d+Au and Au+Au collision systems to study the modification of heavy flavor production in a deconfined medium.Speaker: Laura Patel
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Study of dynamical net charge fluctuations in Au+Au collisions at \sqrt{s_{NN}} = 39 GeV at STAR. 2hThe STAR experiment at Relativistic Heavy Ion Collider (RHIC) investigates the behaviour of strongly interacting matter at high density and searches for the possible formation of Quark Gluon Plasma (QGP). Event-by-event net charge fluctuation has been proposed as one of the indicators of QGP formation in heavy ion collisions. The fluctuation in net charge depends on the squares of the charges present in the system, which depends on the state from which it originates. The system passing through a QGP phase which has quarks as charge carriers, should result in a significantly different net charge fluctuation as compared to Hadron Gas (HG). The variance of the ratio of positive and negative charges scaled by the total charge particle multiplicity (a quantity called D) is approximately 4 times smaller for QGP as compared to HG [1]. We will present preliminary results on net charge fluctuations for Au+Au collisions at \sqrt{s_{NN}} = 39 GeV and will also present their dependence on energy and collision centrality by comparing to the published results [2].Speaker: Bhanu Sharma (Panjab University)
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Study of hyperon-hyperon correlations and search for the H-dibaryon with the STAR detector at RHIC 2hThe production of large number of multi-strange hyperons per central nucleus-nucleus collision at RHIC allows us to study hyperon-hyperon interactions through measurement of particle correlations and search for exotic particles like dihyperons. In 1977 Jaffe[1] predicted a six quark state, $H_{0}$-dibaryon, with hypercharge (Y) = 0 and Strangeness (S) = -2 to be stable against strong decay, but not to weak decay. It has been proposed that the $H_{0}$ would appear as a bump in the $\Lambda-\Lambda$ invariant mass spectra if the $H_{0}$ is a resonance state, or it would lead to a depletion of the $\Lambda-\Lambda$ correlation near the threshold if the $H_{0}$ is weakly bound, which can be used to probe whether there is a stable $H_{0}$ or resonance. Considerable experimental efforts have been devoted to search for $H_{0}$. However there is no conclusive experimental evidence for a bound $H_{0}$. In addition to $H_{0}$, many other dihyperon states have been predicted thoeretically. However, very few measurements are available due to low multiplicity of hyperon production in early nuclear collisions. Recently STAR has collected unprecedented high statistics data for Au+Au collision at RHIC, which provides a unique opportunity to look for the exotic particles and hyperon-hyperon correlations. In this talk, we will present the measurement of $\Lambda-\Lambda$ correlations for $\sqrt{s_{NN}}$ = 39-200 GeV in Au+Au collisions using the STAR experiment at RHIC. In addition to that, we will also present measurements of $\Lambda-\bar\Lambda$, $\Lambda-\Xi^{-}$ correlations for $\sqrt{s_{NN}}$ = 200 GeV in Au+Au collisions. [1] R. L. Jaffe,Phys. Rev. Lett. 38,195(1977).Speaker: Ms Neha Shah (University of California Los Angeles)
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Study of identified particle higher harmonics azimuthal anisotropy in 200GeV Au+Au collisions at RHIC-PHENIX experiment 2hAzimuthal anisotropy and particle species dependence of transverse momentum distribution have been studied actively because they reveal information about the QGP generated in high energy heavy ion collisions. From the study of elliptic event anisotropy v_{2}, we have understood that azimuthal anisotropy is generated by initial participant geometry, with a role for the QGP property $\eta$/s (the ratio of shear viscosity($\eta$) to entropy density(s)). In recent years, higher harmonics azimuthal anisotropies v_{n$\ge$3} are in focus because they are expected to be more sensitive to initial participant geometry and $\eta$/s than will be v_{2}. The observed similarities and differences of identified particles v_{3}, v_{4} and v_{2} will be shown and discussed. The freeze-parameters such as freeze-out geometry and expansion velocity as well as temperature at the freeze-out will also be extracted based on the Blast-Wave model and compared with other measurements like HBT and spectra.Speaker: Sanshiro for the PHENIX experiments Mizuno (University of Tsukuba, RIKEN (JP))
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Study of quark energy loss via Drell-Yan process in p+A collisions at Fermilab E906/SeaQuest experiment 2hE906/SeaQuest is a fixed-target experiment operated at Fermi National Accelerator Laboratory. Using the 120 GeV proton beams from the Main Injector, E906/SeaQuest measures the Drell-Yan production in the dimuon mass region of 4-8 GeV in p+p and p+A collisions over a wide xF range. Parton energy loss in QGP is considered as the dominant mechanism of the observed jet-quenching phenomena at RHIC and LHC. In order to clearly estimate the energy loss effect in QGP possibly formed in A+A collisions, a benchmark of parton energy loss in cold (or normal) nuclear matter, established from p+A collisions, is indispensible. Since the center-of-mass energy of p+A collisions is low and the antiquarks of nucleons inside nuclei sit out of the nuclear shadowing region in E906/SeaQuest, our measurementof quark energy loss via Drell-Yan process will provide the first clean determination of parton energy loss effect in cold nuclear medium. E906/SeaQuest has been taking data since February 2012 and will continue to the end of April of this year. We will present the current status and the prospect of the parton energy loss measurements.Speaker: Dr Kun Liu (Los Alamos National Laboratory)
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Study of single-muon and J/Ψ production in pp collisions at √s = 2.76 TeV as a function of multiplicity with ALICE 2hThe high energy density reached in pp collisions at LHC could be comparable with the energy density for heavy–ion collisions at lower energies (i.e. Au-Au collisions at RHIC) and it might lead to the observation of collective phenomena. The multiplicity of the collision can be used as the “centrality” variable in pp collisions at LHC. In particular, the LHC provided p-p collisions at √s = 2.76 TeV, the same energy per nucleon-nucleon collisions studied in Pb-Pb. These data were already used as a reference to measure the nuclear modification factor (RAA) of J/Ψ production in Pb-Pb collisions. One can search for possible collective effects in pp collisions by studying the multiplicity dependence of various observables commonly studied as probes of the Quark Gluon Plasma in heavy-ion collisions. In particular, this study will present results on the production of single-muon and J/Ψ at forward rapidity as a function of the charged particle density measured at mid-rapidity in pp collisions at 2.76 TeV with the ALICE detector.Speaker: Tinku Sarkar - Sinha (Saha Institute of Nuclear Physics (IN))
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Study of the production of B mesons in pp and Pb-Pb collisions using displaced electrons in ALICE 2hHeavy quarks are expected to be a probe providing new constraints on partonic energy loss mechanisms in the medium produced in heavy-ion collisions at the LHC. In particular, the medium-induced parton energy loss is expected to depend on its mass and colour charge. The measurement of heavy quark production in pp collisions provides an important test of pQCD calculations and serves as a baseline for studies in heavy-ion collisions. The production of electrons from beauty hadron decays can be measured using their displacement from the primary vertex. The pt differential production yields of electrons from beauty hadron decays have been measured at mid-rapidity (|y| < 0.8) in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV by the ALICE experiment at the LHC in the transverse momentum range 1.5 < pt < 6 GeV/c. The pt dependence of the nuclear modification factor R_AA has been calculated with respect to a pp reference obtained from the cross section measured at sqrt(s) = 7 TeV and scaled to sqrt(s) = 2.76 TeV. We present the spectra in pp and Pb-Pb collisions and the nuclear modication factor of electrons from beauty decays for different centrality classes.Speaker: Min Jung Kweon (Ruprecht-Karls-Universitaet Heidelberg (DE))
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Study of the production of B-decay electrons at high momentum in pp collisions at sqrt(s)=7 TeV using secondary vertex reconstruction in ALICE 2hHigh-energy heavy-ion collisions at the LHC allow for the study of the properties of the quark-gluon plasma (QGP). Heavy quarks, charm and bottom, produced in the initial hard scattering processes of the collision are excellent probes of the QGP. When heavy quarks traverse the QGP they are expected to lose energy and such energy loss is predicted to be smaller than for gluons and light quarks. On the other hand, recent experimental data indicate larger energy loss than expected. Heavy flavour production can be studied using electrons from semi-leptonic decays of D and B mesons. The separation of electrons from these two sources (charm and bottom) is of crucial importance to address the expected mass dependence of energy loss. In this poster, we present the measurement of electrons from bottom in the transverse momentum range of 7-12 GeV in 7 TeV p-p collisions. The ALICE EMCal detector possesses outstanding particle identification for electrons at high pT. Two-track secondary vertices with these electrons and surrounding charged tracks are reconstructed, exploiting the tracking precision provided by the Inner Tracking System, and are used to select displaced decay vertices of B mesons. The cross section for bottom-decay electrons is compared to FONLL pQCD predictions and it serves as a reference for studies of B meson suppression in Pb-Pb collisions.Speaker: Tomas Aronsson (Yale University (US))
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Suppression of D-mesons production at relativistic heavy ion collisions 2hCharm quarks/antiquarks produced in the initial stage of heavy ion collisions, would traverse the quark gluon plasma, colliding with quarks and gluons and radiating gluons before appearing as D-mesons. Thus the final spectra of D-mesons would contain information of the medium modification suffered by the charm quarks/antiquarks. We have made a detailed study for the nuclear modification factor of production of D-mesons from the initial fusion of partons in a nuclear collision at RHIC and LHC energies. As a first step, we made a comparative study of some of the energy loss formalisms of charm quarks/antiquarks available in the literature with the same initial conditions [1]. We consider both the radiative and collision energy loss along with longitudinal expansion of the plasma for the prediction of nuclear modification factor. As at RHIC and LHC energies, parton densities reach very high values leading to effective nuclear shadowing, we use the modified structure functions due to shadowing effect given by EKS98 group, in 1998 [2]. Peterson fragmentation function [3] is used for fragmentation of Charm quarks/antiquarks into D-mesons. We have seen that our result can satisfactorily explain the ALICE experimental data for nuclear modification of D-mesons at Pb+Pb collision @ 2.76 ATeV. The result with a recent radiative energy loss calculation [4] has an increasing trend at high transverse momentum and explains the nuclear modification for transverse momentum up to 15 GeV very well. The inclusion of collisional energy loss of charm quarks/antiquarks further suppresses the muclear modification factor of D-mesons. 1. Umme Jamil and Dinesh K Srivastava, J. Phys. G: Nucl. Part. Phys. 37 (2010) 085106 2. K. J. Eskola, V. J. Kolhinen and C. A. Salgado Eur. Phys. J. C 9 (1999) 61 3. C. Peterson, D. Schlatter, I. Schmitt and P. Zerwas, Phys. Rev. D27 (1983) 105 4. R. Abir, U. Jamil, M. G. Mustafa and D. K. Srivastava, arXiv:1203.5221 [hep-ph].Speaker: Dr Umme Jamil Begum (Debraj Roy College, Golaghat, Assam, India)
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Systematic study of the dipolar flow associated with initial density fluctuations in heavy ion collisions at RHIC and LHC within a multi-phase transport (AMPT) model 2hThe anisotropy associated with the initial dipole asymmetry in heavy ion collisions is studied via the first harmonic coefficient $v_{1,1}$ of the two-particle azimuthal angle correlations, within AMPT and HIJING model (AMPT is essentially HIJING + parton/hadron transport). For a broad selection of centrality, transverse momenta and pseudorapidity ($\eta$), a fitting method is used to decompose $v_{1,1}$ into a rapidity-even component, characterized by the Fourier coefficient $v_1$, and a global momentum conservation component. We found that the $v_{1,1}$ data from HIJING can be entirely described by the momentum conservation component, while description of the data from AMPT requires both components. This proves that the rapidity-even $v_1$ is indeed a collective phenomena transferred from initial dipole asymmetry by the strong final state interaction. The extracted $v_1$ values are negative for pT < 0.7-0.9 GeV, reach a maximum at 2-3 GeV, and decreases at higher pT. The $v_1$ values vary weakly with $\eta$ and centrality, but increase with collision energy, strong coupling constant ($\alpha_s$) and parton cross-section ($\sigma$). We compare our results with ATLAS $v_1$ data extracted from same two-component fit [1]. This comparison allows us to constrain $\alpha_s$ and $\sigma$, and consequently the values of shear viscosity. We analyze the values of the extracted global momentum conservation component and compare with those calculated based on Borghini et.al. [2]; the comparison suggests that the effective size of the system that conserve momentum is about 1/3 of the total multiplicity of the event, also consistent with the ATLAS data. We then extract $v_1$ using the modified event plane method proposed by Luzum et.al. [3] and compared with those obtained from two-particle correlation. The differences between the two methods, and consequently the caveat for applying this event plane method to experimental analysis, are discussed. Finally, we extend our simulation to identified particles (proton, kaon and meson). This extension allows us to predict/test the constituent quark scaling which was only done before for higher-order harmonic flow. These studies represent a significant extension of our results presented in a recent publication [4]. [1] ATLAS Collaboration, "Measurement of the azimuthal anisotropy for charged particle production in sqrt(s_NN) = 2.76 TeV lead-lead collisions with the ATLAS detector", arXiv:1203.3087 [hep-ex]. [2] N.Borghini, P.M.Dinh, J.-Y.Ollitrault, A.M.Poskanzer, S.A.Voloshin, "Effects of momentum conservation on the analysis of anisotropic flow", Phys.Rev.C 66, 014901 (2002), [nucl-th/0202013]. [3] M.Luzum and J.Y.Ollitrault, "Directed flow at midrapidity in heavy-ion collisions", Phys.Rev.Lett. 106, 102301 (2011), arXiv:1011.6361 [nucl-ex]. [4] J.Jia, S.K.Radhakrishnan and S.Mohapatra, "A study of the anisotropy associated with dipole asymmetry in heavy ion collisions", arXiv:1203.3410 [nucl-th].Speaker: Sooraj Krishnan Radhakrishnan (State University of New York (US))
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The Effect of 3<->2 Rates on Thermalization in Covariant Transport 2hWe employ a grid based stochastic technique to solve the on-shell Boltzmann transport equation including inelastic 3<->2 processes. The case of an interacting massless partonic gas in a longitudinally expanding Bjorken geometry is considered. The numerical accuracy of the algorithm is first rigorously established from comparisons to both static box calculations and earlier results from the MPC cascade with 2<->2 interactions. We then study the effect of inelastic 3<->2 collision rates and particle production on thermalization, chemical equilibration, and entropy production in the partonic system.Speaker: Mr Dustin Hemphill (Purdue University)
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The effect of initial fluctuations on jet quenching 2hThe effect of initial fluctuations on partonic jet energy loss in a hydrodynamical background in high-energy heavy-ion collisions is studied within a next-to-leading order (NLO) perturbative QCD parton model. An energetic parton jet is found to lose more energy loss with fluctuating initial conditions than that with smooth initial conditions due to initial dominative positive correlation between the fluctuation of the production probability of the initial parton jet and the fluctuation of the local medium density in the jet trajectory. The deviation between the nuclear modification factors with fluctuating initial conditions and smooth initial conditions in non-central A+A collisions is found greater than in central A+A collisions. Particularly, the jet energy loss with linear path-length dependence is found to encounter more stronger fluctuation effect than with quadratic path-length dependence.Speaker: Dr Hanzhong Zhang (Institute of Particle Physics, Central China Normal University)
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The Emergent QCD Plasma from RHIC to LHC 2hOne of the main discoveries at RHIC is the strongly coupled quark-gluon plasma (sQGP), based particularly on the observed "perfect fluid" and strong jet quenching. One of the most interesting physics to see at LHC is whether and how such sQGP properties will change. Based on the deep and generic electric-magnetic duality, we've suggested that the QCD plasma contains the quarks and gluons (color-electric D.o.F) as well as the EMERGENT monopoles (color-magnetic D.o.F.) with the latter becoming dominant at strong gauge coupling as in the near-Tc QCD plasma . An important prediction of this "magnetic scenario" is a RAPID turn-off of the magnetic dominanace when increasing temperature beyond the near-Tc regime of 1-1.5Tc, accompanied by rapid decrease (due to non-perturbative running) of QCD coupling in this regime. This scenario, therefore, implies the QCD plasma to be less perfect a fluid and more transparent a medium at LHC, despite only modest increase in tempearture. We will discuss such expected change of the emergent QCD plasma from RHIC to LHC energies. Furthermore, we will examine the changes in the two most important medium properties: 1) evidences for a less perfect fluid from our molecular dynamics simulations as well as from other groups' hydrodynamic modelling of flow data at LHC; 2) evidences for a more transparent medium as predicted from our analysis of geometric data for jet quenching and from other groups' modelling for LHC Raa data and extraction of jet quenching parameter at LHC. Reference: arXiv:1109.0271[nucl-th]; arXiv:1202.1047[nucl-th]; Phys.Rev. C84 (2011) 034904; PRL102:202302,2009; PRL101:162302,2008; PRC75:054907,2007.Speaker: Jinfeng Liao (Indiana University & RIKEN BNL Research Center)
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The eta dependence of charged particle v_n measurements using the Silicon Vertex detector at RHIC-PHENIX 2hIn heavy-ion collisions, measurement of azimuthal anisotropy in emitted particle momentum distribution is a one of the important themes for the investigation of Quark Gluon Plasma (QGP). For this measurements, we need to be able to measure the reference reaction/event planes direction with good accuracy. In 2011 the Silicon Vertex detector (VTX) was installed in the RHIC-PHENIX experiment. The VTX is composed of four layers, in which the inner two layers are built with pixel detectors and the outer two layers are built with strip detectors. The VTX can reconstruct charged particle tracks and identify hadrons that include c/b-quark. The reaction plane reconstructed using the VTX is expected to have good resolution due to the wide eta acceptance of the detector, -1 to +1. One of the main purposes of VTX detector is to enable the measurement of the second and higher-order azimuthal anisotropy (v2,v3) of heavy quarks. In this presentation, we will discuss the performance of the VTX detector in reaction plane resolution, as well as event plane correlations between different harmonic orders and between silicon and non-silicon detectors which have different eta acceptance. The eta dependence of higher order anisotropy will also be shown as part of a detailed investigation of non-flow effect as a function of eta-gap.Speaker: Mr Hiroshi Nakagomi (Univ. of Tsukuba)
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The Hadron Resonance Gas at the Boundary of the Hadronic World 2hWe investigate the impact of interactions in the hadron resonance gas (HRG) modelled by a volume assigned to the hadrons in a thermodynamically consistent way. We discuss the influence of the hadron radius, a parameter of the model, on thermodynamic quantities as energy density, entropy density and pressure. The consideration of interactions is followed by us arguing that the commonly used free HRG is not an appropriate description in the dense environment near the phase boundary/rapid cross-over and shows in this region clear signs of the Hagedorn divergence. This is tamed in our model including interactions, so that we associate the strong rise of the thermodynamic quantities observed in recent lattice quantum chromodynamics calculations with deconfinement.Speaker: Michael Winn (Ruprecht-Karls-Universitaet Heidelberg (DE))
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The importance of e+A collisions at an Electron-Ion Collider 2hOver the last decade, there has been a plethora of new and exciting results in heavy-ion collisions emanating from the CERN and Brookhaven Laboratories. These results have led to a sea change of the view on how the evolution of a high energy heavy-ion collision proceeds. What has become apparent is that in order to validate claims of perfect fluidity, for example, the initial conditions at small-x need to be well understood. Whilst d+A and p+A collisions provide a handle on some of these effects, for precision measurements and precise knowledge of the kinematics, e+A collisions become essential. A proposal has been developed at Brookhaven National Lab to add an electron accelerator to the current RHIC complex, providing for electron beams ranging from 5 GeV to 30 GeV. Complementing the programme on polarised e+p scattering, a broad programme on e+A physics is envisioned which will range from investigating saturation physics at low-x to hadronization at high-x. In this poster, I will show the recent progress made on the golden measurements which were identified in the proceedings of the Fall programme at the INT [1]. [1] “Gluons and the quark sea at high energies: Distributions, polarization and tomography.”,Eds D. Boer, M. Diehl, R. Milner, R. Venugopalan, W. Vogelsang, BNL-96164-2011, INT-PUB-11-034, JLAB-THY-11-1373Speaker: Matthew Lamont (BNL)
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The Micro-Vertex-Detector of the CBM-Experiment 2hThe Compressed Baryonic Matter Experiment (CBM) is one of the core experiments of the future FAIR facility at Darmstadt/Germany. The experiment will explore the phase diagram of hadronic matter in the regime of highest baryon densities. Nuclear fireballs created in heavy ion collisions of 8-45 AGeV beam energy will be studied with numerous probes, among them open charm. Reconstructing those rare probes requires a vacuum compatible micro vertex detector (MVD) with unprecedented properties. Its sensor technology has to feature a spatial resolution of <5μm, a radiation tolerance of >10e13 n/cm² and a time resolution of few 10 μs. The detector station must combine an active cooling of the sensors (~1W/cm²) with a material budget below few 0.1% radiation length. To match those requirements, we rely on the CMOS Monolithic Active Pixel Sensors provided by the IPHC Strasbourg. The highly granular and 50 μm thin sensors will be mounted on a cooling support made from CVD diamond. This support drives the dissipated power to a heat sink outside the detector acceptance. The readout of the sensors will be done by means of ultra-thin flex print cables. We discuss the concept of the CBM MVD and report about the status of our prototyping.Speaker: Tobias Tischler (Goethe-Universität, Frankfurt)
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The PHENIX Forward Silicon Vertex Detector 2hTwo Forward Silicon Vertex Trackers (FVTX) have been installed at the PHENIX Experiment at RHIC, and extend the precision vertex capability of the PHENIX Silicon Vertex Trackers (VTX) to forward rapidity. The FVTX consists of two endcaps, with four silicon mini-strip planes each, covering the angles from ~10 to 35 degrees (1.2< |y|<2.2) that match the two existing PHENIX muon spectrometer arms. Each silicon plane consists of 48 wedges of mini-strips with 75 micron pitch in the radial direction and lengths in the phi direction varying from 3.4 mm at the inner radius to 11.5 mm at the outer radius. The FVTX has about 0.54 million strips in each forward detector that are read out with FPHX chips which are wire bonded directly to the mini-strips. This chip provides analog and digital processing with zero-suppression and produces a digital output which is data-pushed at 200 Mbps to an intelligent readout board (ROC) containing Field-Programmable Gate Arrays. The maximum occupancy reached in central Au-Au collisions is less than 3%. With an expected distance of closest approach (DCA) resolution of 200 microns or better at 5 GeV/c, we will improve tracking from the original collision vertex and be able to identify secondary particles from in-flight decays. The detector performance during the 2012 RHIC Run will be discussed.Speaker: J. Matthew Durham (Los Alamos National Laboratory)
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The RICH detector for the Compressed Baryonic Matter experiment 2hThe Compressed Baryonic Matter experiment, CBM, is being built at the Facility for Antiproton and Ion Research, FAIR, at Darmstadt. The goal is to investigate the QCD phase diagram in particular in the region of high net baryonic density, using heavy ion collisions in a fixed target experiment at beam energies ranging from 8 to 45 GeV/nucleon. The high beam intensity and -quality of the SIS300 accelerator (SIS100 in the first step), together with a detector concept optimized for high event rate capability, allow to achieve exceptional high luminosities (reaction rates up to 10 MHz) and to study in particular rare probes. Of particular interest are dilepton probes originating from decays of charmonium and light vector mesons, such as rho/omega -> e+ e-/ mu+ mu-. These dilepton probes do not interact hadronically with the dense medium and as such allow to probe the early, high density phase of the fireball evolution. In the CBM detector setup, a Ring Imaging Cherenkov Detector (RICH) will be used to provide clean separation of electrons from pions, and together with additional layers of Transition Radiation Detectors (TRD) to achieve pion suppression factors up to 4 orders of magnitude. The RICH detector will consist of a CO2 gas radiator volume, a spherical focusing mirror, and multi-anode PMTs (ca 55k individual channels) for detection of Cherenkov photons. A major step in the detector development was the test of a quasi full-scale prototype of the RICH detector at CERN in autumn 2011. Valuable information on the ring image resolution, the photon statistics, the MAPMT readout, and the overall operation was obtained. We report on the design and status of the RICH detector development, and in particular on the beam time results obtained with the RICH prototype.Speaker: Jan Kopfer (Universität Wuppertal)
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The shape of event-to-event fluctuations in heavy-ion collisions 2hWe report results from a new study of lattice QCD with decreased lattice spacing and using two flavours of light dyanamical quarks at finite temperature and chemical potential through the method of Taylor series expansions. With a factor of two in lattice spacings covered to date, the approach to the continuum limit is controlled better. In units of the inverse Compton wavelength of the light pion, the lattice volumes remain as large as before. We construct ratios of susceptibilities along the freezeout curve, thus improving upon previous results and allowing us to make more reliable predictions of the results of experiments on the shape of event-to-event fluctuations of various conserved quantities in heavy-ion collisions.Speaker: Sourendu Gupta (Tata Institute of Fundamental Research)
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The Tungsten-Scintillating Fiber Accordion Electromagnetic Calorimeter for the sPHENIX Detector 2hThe PHENIX Experiment is planning a major upgrade to enhance its capabilities to measure jets in heavy ion collisions, as well as in p+A, polarized proton, and eventually e-A collisions at the Electron Ion Collider. One of the major new components of this upgrade will be a new compact electromagnetic calorimeter covering ±1 units in pseudorapidity and 2 in phi. It will consist of a matrix of tungsten plates, tungsten powder, scintillating fibers and epoxy formed into an accordion structure that will have a small Moliere radius and short radiation length, thus allowing the calorimeter to have a high degree of segmentation for measuring jets at a relatively small radius and providing a compact design for the sPHENIX detector. The scintillating fibers will be read out using silicon photomultipliers that will be required to operate in the fringe field of the sPHENIX solenoid magnet and will include a new electronic readout system. The overall design of the calorimeter will be described, along with the R&D effort currently under way to develop the detector and its expected performance based on Monte Carlo simulations.Speaker: Dr Craig Woody (Brookhaven National Lab)
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The tunnelling effect and the crossover of deconfinement in FL model 2hWe have discussed the tunnelling effect in FL model. The tunnelling coefficient is derived in the field configuration space by calculating the transition amplitude using the path integral at SPA and the dilute instanton gas approximation. By studying the tunnelling effect between the two degenerating vacuums at the critical temperature and chemical potential, we find that the system could be deconfined by tunnelling, which will change the first order deconfinement phase transition to crossover. The $T-\mu$ phase diagram of deconfinement with both first order phase transition and crossover including CEP is presented.Speaker: Dr Song Shu (Faculty of Physics and Electronic Technology, Hubei University, China)
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The universality of eta/s 2hALICE, ATLAS and CMS detectors at LHC and previously PHENIX and STAR detectors at RHIC have provided compelling evidence for higher order flow components apart from the elliptic flow v2. It is by now well established that both RHIC and LHC have produced a ”perfect fluid” of Quark Gluon Plasma with eta/s close to zero, as predicted by AdS/CFT limit. One expects that higher order harmonics and in particular triangular flow v3 will constrain eta/s more precisely. Although, the particle density per participant pair at 2.76 TEV (LHC) is a factor of 2.15 higher than at RHIC, eta/s remain almost the same going from RHIC to LHC. It is known that [1] eta/s / 1/g4 and 1/g2 [ln(T/T )]2, thus /s becomes and increasing function of the temperature. However, a simple [2] estimate indicates, that the initial temperature for eta/s 0.08 changes from 360 MeV for RHIC to 530 MeV for LHC. Given the logarithmic dependence of /s on the temperature, it is almost natural that /s at LHC (2.76 TeV) does not changes perceptibly going from RHIC to LHC [3]. Our prediction is that even for the highest energy of LHC, eta/s will not change perceptably. The second great puzzle is the universality of /s 1/4, applicable across a large number of phenomena, dra- matically different from each other. Ultracold quantum degenerate strongly interacting atomic Fermi gas, Graphene, even Giant resonances in finite nuclei exhibit the same behavior of /s 1/4. It is remarkable that both the coldest and hottest matter on earth are rather similar. This universaility is a direct consequence of strong coupling due to many body interaction leading to observable correlation. This observation will be presented. References: [1] J. I. Kaputs, J. of Phys. G34 (2007)S295-S303 and references therein. [2] A.K. Chaudhuri and Bikash Sinha, to beSpeaker: Bikash Sinha
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Theoretical Predictions for Nuclear Effects in the Asymmetric Collisions of the LHC at 4.4 ATeV 2hAsymmetric high-energy proton-nucleus collision can give unique test of the high-energy nuclear effects. This case nuclear modification and rapidity asymmetry can be describe in parallel [1]. Moreover, measurements might enable us to separate or at least understand better the the mechanisms of the final and initial state nuclear effects in nucleus-nucleus collisions. Predictions for nuclear effects in proton-nucleus (pA or dA) are presented here in wide rapidity ranges (both forward and backward directions) at 200 AGeV RHIC and 4.4 ATeV LHC energies similarly as in Ref[2] for midrapidity. We used a collinear factorized perturbative QCD-improved parton model [3] calculations, including various types of nuclear shadowing parameterizations and models for multiple scattering. We determined the nuclear modification factor, R_{pPb}(p_T) and rapidity asymmetry, Y_{asym}(p_T) and their uncertainties. The scaling behavior of these effect and separation method is also presented. [1] A Adeluyi et al. Phys.Rev. C80 (2009) 014903 [2] G.G. Barnaföldi et al Phys.Rev. C85 (2012) 024903 [3] Y. Zhang et al. Phys.Rev. C65 (2002) 034903Speaker: Gergely Barnafoldi (Hungarian Academy of Sciences (HU))
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Theory and phenomenology of quarkyonic percolation of finite density QCD matter 2hWe generalize the percolating transition discovered in [1] to the full phase diagram, exploring the onset of "quarkyonic percolation" for SU(N) Yang-Mills matter when baryon density, temperature and number of colors are varied. We show that percolation's dependence on number of colors is different from deconfinement, suggesting that the two phases are generally distinct, with the percolating phase being similar to the quarkyonic phase conjectured in [2]. We find that, in our world (3 colors, 2-3 flavors) a percolating but confined phase can arise at 2-3 times nuclear density and moderate temperature. The new phase is confined and contains baryons, yet quark-hole states can propagate to arbitrary distances due to the onset of percolation of tunneling transitions across baryons. We conclude by sketching an effective theory of percolating matter, and suggesting experimental signatures of it in lower energy heavy ion collisions (FAIR,NICA and the RHIC low energy scan) as well as within neutron stars and supernovae. Based on [1] and [3] [1] S.Lottini and G.Torrieri, Phys.Rev.Lett. 107 (2011) 152301 [2] L.Mclerran, R.Pisarski, Nucl.Phys.A796:83-100,2007 [3] S. Lottini and G.Torrieri, http://arxiv.org/abs/1204.3272Speaker: Giorgio Torrieri (JW Goethe Universitat, Frankfurt)
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Thermal meson properties and chiral symmetry: recent advances. 2hI will review recent and ongoing work on thermal meson properties relevant for the hadron gas regime in Relativistic Heavy Ion Collisions. These include transport coefficients, chemical nonequilibrium, susceptibilities, isospin breaking and different aspects on chiral symmetry restoration and the QCD transition. The basic framework is the use of Chiral Effective Lagrangians which ensure the model independency of the low-energy and low-temperature regimes and allows to include interactions consistently. This is combined with unitarity when an accurate analytical description of particle scattering is needed, as in the case of resonance studies, virial analysis and transport coefficients, for temperatures and energies where deviations from Chiral Perturbation Theory are significant. Our scheme provides an adequate phenomenological description for several quantities. The shear viscosity is compatible with the KSS bound and recent data on elliptic flow, bulk viscosity correlation with the trace anomaly is established without appealing to the spectral function profile and the electrical conductivity is consistent with the low-energy photon spectrum. At the same time, this framework helps to understand theoretical aspects such as the role of scalar resonances and degeneration of partners in chiral restoration or the effects of meson interactions in a possible window between chemical and thermal freeze-out. We will pay also attention to the connection with lattice results, particularly in the analysis of connected and disconnected scalar susceptibilities, whose quark mass and temperature behaviour we can establish rigorously from our isospin-breaking analysis, providing then a useful benchmark for the continuum limit. Some related references: - D.Fernandez-Fraile and A.Gomez Nicola, ``The Electrical conductivity of a pion gas'', Phys.Rev. D {\bf 73}, 045025 (2006) [arXiv:hep-ph/0512283]. - D.Fernandez-Fraile, A.Gomez Nicola and E.T.Herruzo, ``Pion scattering poles and chiral symmetry restoration'', Phys.Rev. D {\bf 76}, 085020 (2007) [arXiv:0707.1424 [hep-ph]]. - D.Fernandez-Fraile and A.Gomez Nicola, ``Transport coefficients and resonances for a meson gas in Chiral Perturbation Theory'', Eur.Phys.J. C {\bf 62}, 37 (2009) [arXiv:0902.4829 [hep-ph]]. - D.Fernandez-Fraile and A.Gomez Nicola, ``Bulk viscosity and the conformal anomaly in the pion gas'', Phys.Rev.Lett. {\bf 102}, 121601 (2009) [arXiv:0809.4663 [hep-ph]]. - D.Fernandez-Fraile and A.Gomez Nicola, ``Chemical nonequilibrium for interacting bosons: applications to the pion gas'', Phys.Rev. D {\bf 80}, 056003 (2009) [arXiv:0903.0982 [hep-ph]]. - A.Gomez Nicola and R.Torres Andres, ``Isospin Breaking and chiral symmetry restoration'', Phys.Rev. D {\bf 83}, 076005 (2011) [arXiv:1101.5362 [hep-ph]].Speaker: Prof. Angel Gomez Nicola (Universidad Complutense Madrid)
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Thermal Photon emission with partial chemical equilibrium equation of state 2hPhotons are believed to be clean and penetrating probes of the medium created in ultra-relativistic heavy-ion collisions. The thermal photon spectra and their anisotropy are known to be very sensitive to the thermalization time, the specific shear viscosity, the equation of state of produced matter, and the initial state fluctuations [1]. Previous computations of photon emission spectra have been mostly carried out in a fully thermalized medium evolving dynamically under the influence of an equation of state with a first order phase transition. Today, a realistic state-of-the-art equation of state based on lattice QCD results and partial chemical equilibrium (PCE) in the hadronic phase is available for relativistic hydrodynamic simulations [2]. The non-zero chemical potentials will enhance thermal photon production rates in the hadronic phase by their corresponding non-equilibrium fugacity factor ~ e^{mu/T}. However, the breaking of chemical equilibrium below the quark hadron phase transition also changes the relation between temperature and energy density, which results in faster cooling evolution during the hadronic phase. This reduces the space-time volume for photon emission from the hadronic phase. In this work, we study PCE effects on the yields and the azimuthal anisotropies of produced thermal photons in heavy-ion collisions at RHIC and LHC energies, using a realistically evolving hydrodynamic medium. We study in detail the interplay between the chemical potential enhancement in the thermal photon emission rates and faster cooling evolution of the medium. We compare our calculations with data from RHIC, and make predictions for measurements at the LHC. [1] M. Dion, J. F. Paquet, B. Schenke, C. Young, S. Jeon and C. Gale, "Viscous photons in relativistic heavy ion collisions,'' Phys. Rev. C 84, 064901 (2011) [2] Chun Shen, Ulrich Heinz, Pasi Huovinen and Huichao Song, "Systematic parameter study of hadron spectra and elliptic flow from viscous hydrodynamic simulations of Au+Au collisions at √s_{NN} = 200A GeV,'' Phys. Rev. C 82, 054904 (2010)Speaker: Chun Shen (Ohio State University)
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Thermal photons and dileptons - successes, status, urgency 2hWhile experimentally very demanding, thermal (low pT) photons and dileptons offer unique, direct access to the medium formed in heavy ion collisions, its size, temperature, lifetime, viscosity and other properties. Higher pT jet-medium photons can serve as a control (complementary) probe. On the other hand these measurements are very involved and the interpretation of the results is challenging. We'll present a brief survey of past successes and current status, then assess the future need and realistic possibilities of thermal photon and dilepton measurements in heavy ion collisions.Speaker: Dr Gabor David (Brookhaven National Laboratory)
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Thermal photons from quark matter in presence of strong magnetic field. 2hWe calculate explicitly the thermal quark propagator in presence of magnetic field that is relevant for heavy ion collision experiments at RHIC and LHC. Using this propagator, we calculate the momentum dependent polarization tensor and discuss the relevant collective excitations. Using the same, we also evaluate the thermal photon rate of quark matter in presence of magnetic field. We estimate the photon flux for ultra strong magnetic field that will be of relevance for RHIC and LHC.Speaker: Dr Bhaswar Chatterjee (Physical Research Laboratory, Ahmedabad, India)
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Thermal Photons in Heavy Ion Collisions at RHIC 2hThe hot and dense fireball produced in high energy heavy ion collisions, such as that at RHIC, exhibits complicated dynamics and time evolution. Thermal photons have a negligible cross-section with the medium and so pass through unmodified, thus measuring their properties gives access to the entire time evolution of the fireball. Thermal photons are expected to be observable at low momentum. They compete in yield with photons from hadron decays and, at high momentum (above roughly 4 GeV), direct photons that result from initial hard scatterings of partons in the colliding nuclei. PHENIX has measured the yield of direct photons in Au+Au collisions, as well as the baseline measurements in p+p and d+Au. Recently PHENIX has also measured elliptic flow of direct photons. The latest results on low momentum direct photons will be discussed, including measurements of real photons using photon conversions and a novel method to reduce systematic uncertainties.Speaker: Richard Petti (S)
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Theta vacuum and entanglement interaction in the three-flavor Polyakov-loop extended Nambu-Jona-Lasinio model 2hWe investigate theta-vacuum effects on the QCD phase diagram for the realistic 2+1 flavor system, using the three-flavor Polyakov-extended Nambu-Jona-Lasinio (PNJL) model and the entanglement PNJL model as an extension of the PNJL model. The theta-vacuum effects make the chiral transition sharper. For large theta-vacuum angle the chiral transition becomes first order even if the quark number chemical potential is zero, when the entanglement coupling between the chiral condensate and the Polyakov loop is taken into account.We finally propose a way of circumventing the sign problem on lattice QCD with finite theta.Speaker: Takahiro Sasaki (K)
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Three-Particle Azimuthal Correlations with an Intermediate-$p_T$ Trigger in Pb-Pb at $\sqrt{s_{NN}}=2.76$ TeV in ALICE 2hTri-hadron azimuthal correlations are studied in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV in ALICE. They are analyzed with one intermediate $p_T$ trigger to preferentially select on jets and two lower $p_T$ associated particles. With these correlations interaction of the jets and the medium can be studied. Three-particle correlations can give insight into the sources of modification to the jet shape such as jet deflection by radial flow, $k_T$ broadening, path length dependent energy loss, or conical emission from either \v{C}erenkov gluon radiation or a Mach Cone. In addition, different background subtraction systematics allow us to study three-particle correlations in the $p_T$ region where the flow systematics are very large in two-particle correlations. The dependence of the results on collision centrality and on trigger and associated particle $p_T$ will be presented.Speaker: Jason Glyndwr Ulery (Johann-Wolfgang-Goethe Univ. (DE))
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Time evolution of the sQGP from new solutions of relativistic hydrodynamics 2hThe time evolution of the strongly interacting quark gluon plasma (sQGP) created in relativistic heavy ion collisions can be described by hydrodynamical models. Hadrons are created at the freeze-out of this fluid, thus their distributions reveal information about the final state. To access the time evolution and the initial state, one needs either additional information about the Equation of State (EoS) of this matter, or one needs to analyze penetrating probes, such as direct photon observables. [1] In this talk we review recent hydrodynamic solutions, and show new exact, analytic solutions of hydrodynamics with arbitrary temperature dependent EoS. We investigate special cases of this class of solutions, in particular, we present exact hydrodynamical solutions with the Equation of State determined from lattice QCD calculations. [2] We calculate direct photon spectra, elliptic flow and HBT radii and compare them to recent direct photon measurements performed by the PHENIX experiment at RHIC [3]. The first family of rotating solutions of relativistic and non-relativistic hydrodynamics are also shown [4]. The effect of the total angular momentum of the system on the elliptic flow and HBT radii is also reviewed. It is an important result that elliptic flow may be generated by the rotation of the system. References: [1] "Similar final states from different initial states using new exact solutions of relativistic hydrodynamics." M. Csanad, M. Nagy, T. Csorgo, Eur.Phys.J.ST 155 (2008) 19 and "Initial conditions, equations of state and final state in hydrodynamics." M. Csanad, Acta Phys.Polon. B40 (2009) 1193 [2] "Exact solutions of relativistic perfect fluid hydrodynamics for QCD equation of state" M. Csanad and M. Nagy, in preparation [3] "Equation of state and initial temperature of quark gluon plasma at RHIC" M. Csanad and I. Majer, Centr. Eur. J. Phys., arXiv:1101.1279 [4] "New simple explicit solutions of perfect fluid hydrodynamics and phase-space evolution" M. Nagy, Phys.Rev. C83 (2011) 054901Speaker: Mate Csanad
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Toward radiative transport with improved parton interactions 2hThe Quark-Gluon Plasma can be produced in high energy heavy ion collisions and how it equilibrates is important for the extraction of the properties of strongly interacting matter. A radiative transport model can be used to reveal interesting characteristics of Quark-Gluon Plasma thermalization. For example, screened parton interactions always lead to partial pressure isotropization. Systems with different initial pressure anisotropies evolve toward the same asymptotic evolution. In particular, radiative processes are crucial for the chemical equilibration of the system. Matrix elements under the soft and collinear approximation for these processes as first derived by Gunion and Bertsch are widely used. A different approach is to start with the exact matrix element for the 2<->3 processes as was first conjectured by Parke and Taylor. General features of this approach will be reviewed and the results will be compared with the Gunion-Bertsch results. We will comment on the possible implications of the exam matrix approach on Quark-Gluon Plasma thermalization.Speaker: Bin Zhang (Arkansas State University)
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Transient Fluid Dynamics of a Strongly Coupled N = 4 SYM Plasma 2hWe argue, using the AdS/CFT correspondence, that the transient dynamics of the shear stress tensor in a strongly coupled N = 4 SYM plasma is not described by relaxation-type, fluid dynamical equations: at long times the equations of motion should contain a second-order comoving derivative of the shear stress tensor. This occurs because in this strongly-coupled system the lowest “non-hydrodynamical” quasinormal modes associated with shear stress possess a nonzero real part at zero wavenumber. We use Weyl invariance to obtain the most general equations of motion containing 2 comoving derivatives of the shear stress tensor that are compatible with the symmetries. We show that the asymptotic solution of this theory valid at times much larger than the timescale associated with the “non-hydrodynamical” modes reproduces the well-known results previously obtained directly from the AdS/CFT correspondence. If the QGP formed in heavy ion collisions can be at least qualitatively understood in terms of strongly-coupled N = 4 SYM theory, the second time derivative present in the equations of motion of the fluid may lead to an unexpected dependence on the initial conditions for the shear stress tensor needed in numerical hydrodynamic simulations.Speaker: Jorge Noronha (U)
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Transition From Ideal To Viscous Mach Cones In A Kinetic Transport Approach 2hUsing a microscopic transport model we investigate the evolution of conical structures originating from the supersonic projectile moving through the hot matter of ultrarelativistic particles. Using different scenarios for the interaction between projectile and matter, and different transport properties of the matter, we study the formation and structure of Mach cones. Especially, a dependence of the Mach cone angle on the details and rate of the energy deposition from projectile to the matter is investigated. Furthermore, the two-particle correlations extracted from the numerical calculations are compared to an analytical approximation. We find that the propagation of a high energetic particle through the matter does not lead to the appearance of a double peak structure as observed in the ultrarelativistic heavy-ion collision experiments. The reason is the strongly forward-peaked energy and momentum deposition in the head shock region. In addition, by adjusting the cross section we investigate the influence of the viscosity to the structure of Mach cones. A clear and unavoidable smearing of the profile depending on a finite ratio of shear viscosity to entropy density is clearly visible.Speaker: Ioannis Bouras (University of Frankfurt a.M.)
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Transport Properties of Resonances Gas 2hIn this work, we present how shear viscosity and entropy density behave in the Hadronic system as the number of Resonances produced are increasing. Shear viscosity is calculated by so called Chapman-Enskog approximation and cross-sections used in this calculation are taken from experiments and UrQMD model. One interesting results is we are able to approach the famous 1/4\pi limit for the ratio of shear viscosity to entropy density as we increases the number of resonances in the calculation.Speaker: Anton Wiranata (L)
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Transverse momentum correlations in Pb-Pb collisions at sqrt(NN) = 2.76~TeV 2hWe report on the first study of transverse momentum differential correlation, $\la \Delta p_t \Delta p_t \ra$, in Pb - Pb collisions at \snn~= 2.76~TeV measured with the ALICE detector at the CERN Large Hadron Collider. We measure the two-particle correlation functions for $++$, $--$, and $+-$ charged particle pairs as a function of the pair azimuthal, $\Delta\phi$, and pseudorapidity, $\Delta\eta$, differences, and study their evolution with collision centrality. We find that similarly to number two-particle correlations, the $\la \Delta p_t \Delta p_t \ra$ correlations shape and amplitude exhibit a strong dependence on collision centrality. We further observe they too exhibit near-side ridge-like and double away-side peak structures in most central collisions. We carry out Fourier decompositions of the correlation dependence on $\Delta\phi$ as a function of $\Delta\eta$ and find the harmonics coefficients are essentially constant for $\Delta\eta>0.6$. We compare the measured harmonic coefficients with flow coefficients $v_2$, $v_3$, $v_4$ obtained with the reaction plane method and find that, up to scaling factors that depend on the order of the coefficients, they have identical collision centrality dependence.Speaker: Claude Andre Pruneau (Department of Physics and Astronomy)
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Transverse momentum dependence of the low-mass dielectron enhancement - effects of radial flow 2hPHENIX has measured the e^{+}e^{-} pair continuum in sqrt(s_{NN})=200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e^{+}e^{-} yield is compared to the expectations from hadronic sources, based on PHENIX measurements. We investigate the effects of radial flow on the transverse mass dependence of the dilepton spectrum in min. bias Au+Au collisions in the low mass region. The analysis results will be detailed in the region around the omega and phi mass, 0.7 < m_{ee} < 1.2 GeV as well as in the very low mass of m_{ee} < 0.15 GeV. Current status of the analyis of radial flow effects in the low mass region, 0.15 < m_{ee} < 0.7 GeV as well as consistency checks with HBT measurements will be presented.Speaker: Marton Vargyas (ELTE)
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Transverse momentum fluctuations in event-by-event viscous hydrodynamics 2hResults of event-by-event simulations of a 3+1D viscous hydrodynamic model for Au-Au collisions at 200 GeV are presented. The fluctuations of the average transverse momentum in an event are determined by the fluctuations of the initial transverse size of the fireball. The mechanism involving transverse-momentum fluctuations from the initial size fluctuations, transmitted to the final statistical-hadronization phase with hydrodynamics, is capable of easily reproducing the magnitude of the effect and explains the basic features of the data. The momentum fluctuations present a complimentary information about the collective expansion of the fireball to the widely discussed harmonic flow coefficients. The scaled transverse momentum fluctuations are not changed significantly when modifying the viscosity or the freeze-out temperature. P. Bozek, W. Broniowski, Phys. Rev. C85, 044910 (2012)Speaker: Piotr Bozek
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Turbulent instability in low viscosity quark-gluon plasma 2hFlow asymmetries are in focus of present heavy ion studies. In head-on collisions there would be no reason to have an azimuthal or longitudinal asymmetry, nevertheless, new observations for the higher harmonics show [1] that even in central collisions there is a strong azimuthal asymmetry in the emitted hadrons, and this asymmetry arises from transverse fluctuations of the initial state. This poses a challenge to separate the flow characteristics arising from collective global asymmetries and from random fluctuations. Here we study flow asymmetries arising from global asymmetries in peripheral collisions. The dynamical development of collective flow of prefect QGP fluid is studied in a (3+1)D fluid dynamical model for peripheral heavy-ion collisions, with globally symmetric, initial conditions, which take into account the shear flow caused by the forward motion of the matter on the projectile side and the backward motion on the target side. While at $\sqrt{s_{NN}} = 2.76A$\,TeV semi-peripheral Pb+Pb collisions the earlier predicted rotation effect [2] is visible in the calculations, at more peripheral collisions, with high resolution and low numerical viscosity the initial development of a Kelvin-Helmholtz instability (KHI) is observed [3], which alters the flow pattern considerably. On the initial dividing plane a wave develops, and the dividing plane develops into a turning nonlinear wave. The wave develops only in peripheral reactions with very low numerical viscosity. The KHI wave is visible in the reaction plane if we mark the motion of the fluid which was initially on the dividing plane. The direction of the wave is such that it enhances the rotation effect and increases the asymmetry of the global collective $v_1(y)$. The possibility of turbulence in the transverse plane developing from initial fluctuations was also pointed out recently [4]. Although, the predicted rotation effect is not easily detectable due to longitudinal initial state fluctuations, the KHI enhances the flow asymmetry and changes its pattern in peripheral collisions. The present developments suggest that the global collective $v_1$ flow can be disentangled from random fluctuations. This is necessary to measure the global collective flow in peripheral collisions. The KHI is very sensitive to the magnitude of the viscosity. Thus if this research is successful the analysis of global collective $v_1$ flow as a function of beam energy and impact parameter may provide a precision measurement of viscosity and its variation. [1] K. Aamodt et al., (ALICE Collaboration) Phys. Lett. B708, 249 (2012). [2] L.P. Csernai, V.K. Magas, H. Stöcker, D.D. Strottman, Phys. Rev. C84, 02914 (2011). [3] L.P. Csernai, D.D. Strottman, and Cs. Anderlik, arXiv:1112.4287v1 [nucl-th], and Phys. Rev. C (2012) in press. [4] S. Floerchinger, U.A. Wiedemann, JHEP 11, 100 (2011).Speaker: Laszlo Pal Csernai
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Two Particle Correlation Results from the PHENIX Silicon Vertex Detector (VTX) in Au+Au collisions at 200 GeV 2hTwo particle correlations in azimuth and pseudorapidity encapsulate a wealth of information from jet correlations from medium response to bulk collective flow. The PHENIX Silicon Vertex Detector (VTX) is a cylindrical, 4-layer detector close to the beampipe which extends the PHENIX tracking capability to a pseudorapidity from -1 to +1 and over nearly the full azimuth. The first heavy ion data set with the VTX was taken in 2011 and we will present the latest status on these correlation analysis using this VTX data from 200 GeV Au+Au collisions. Additionally, many frameworks have been proposed for factorizing the above listed physics contributions that will be compared to the experimental data.Speaker: Theodore Koblesky Theo (University of Colorado)
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Two real-size high-rate MRPC modules for CBM-TOF 2hThe Compressed Baryonic Matter experiment at the future Facility for Antiproton and Ion Research will use a time-of-flight (TOF) wall for hadron identification, based on the MRPC technology. The challenge is to keep high efficiencies (above 90%) and good time resolutions (less than 80ps) at particle fluxes up to 20kHz/cm2, which is not accessible to conventional float-glass MRPCs. For this purpose, a type of low-resistivity doped glass with bulk resistivity on the order of 1010 Ωcm was produced at Tsinghua University. Several high-rate prototypes based on this material have been developed and tested in beam. In the current conceptual design, the whole CBM-TOF wall is arranged in four “rate regions”. In the inner region of the wall (region 1), pad readout MRPCs based on low-resistive glass can be efficiently used to cope with the high particle fluxes and granularities (above 20 kHz/cm2), while strip-readout MRPCs represent a natural choice for the outer region where the system occupancy is orders of magnitude lower. Recently, our effort is to realistically adapt the MRPC geometry to suit the conceptual design of the TOF wall. Two kinds of real-size MRPC modules made of low-resistivity doped glass were developed, and beam tested were performed both with protons at the Electron Linac with high Brilliance and low Emittance (ELBE) facility at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). We summarize here the results from the latest beam test of the two real-size modules at ELBE facility at HZDR. The counters show high efficiencies above 90%, and time resolutions (MRPC+FEE) down to 60ps, at particle flux up to 100 kHz/cm2, thus fulfill the CBM requirements.Speaker: Mr Jingbo Wang (Department of Engineering Physics, Tsinghua University, Key Laboratory of Particle & Radiation Imaging, Ministry of Education, Beijing 100084, China)
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Two-baryon correlations in heavy-ion collisions at the LHC 2hIn heavy-ion collisions produced at the LHC a significant number of baryons is emitted in each collision. Two-particle correlations of those baryons carry important information about the emitting source and the interaction between them. At low relative momentum femtoscopic correlations arise, which are sensitive to the homogeneity lengths of the system. Hydrodynamic models predict that these will decrease with increasing transverse mass of the pair. Such a decrease is universally reported for pions, also at the LHC. Baryons, having a much larger mass, allow to significantly extend the range of measured m_T. The results from baryon femtoscopy would put a strong constraint on such predictions. Non-identical baryon pairs are also sensitive to emission asymmetries. Femtoscopic correlations between baryons arise mostly due to the strong interaction, which is not precisely known for some baryon pair types. The most notable example is the lambda-lambda interaction which has an unknown contribution due to the potential existence of the H0 dibaryon. Equally interesting are baryon-antibaryon potentials, which have significant contributions from annihilation channels. These processes may have an impact on single-particle spectra, and should be investigated as one of the possible sources of the small proton yield at the LHC. We show the two-particle correlation functions for several pair types (both baryon-baryon and baryon-antibaryon) composed of protons and lambdas. Femtoscopic analysis is carried out for proton pairs, taking into account residual correlations and annihilation channel for the proton-antiproton system. Correlations with lambdas are also analyzed, both with femtoscopic methods as well as to study the unknown interaction potentials.Speaker: Jai Salzwedel (Ohio State University (US))
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Two-particle correlations on transverse momentum in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at STAR. 2hCorrelations on transverse momentum $p_t$ include important aspects of the six dimensional correlation space ($p_t1,\eta_1,\phi_1,p_t2,\eta_2,\phi_2$) [1]. Two-particle 2D correlations, $(p_t1,p_t2)$, for minimum-bias Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV from STAR show a broad peak extending from 0.5-4.0 GeV/c [2]. These correlations are formed from all charged particles with $p_t \geq 0.15$ GeV/c, $|\eta| \leq 1$, and $2\pi$ azimuth. The broad peak is observed in both like- and unlike-sign charge combinations and same- and away-side relative azimuth angles. Variation of peak positions and widths will be reported as a function of centrality. Interestingly, the peak in the data for away-side or “back-to-back” pairs persists even in more-central collisions, remaining at approximately the same transverse momentum for like- and unlike-sign pairs at all centralities. The event generator HIJING, often used to model peripheral heavy ion interactions, predicts a similar peak in this momentum range but only when jets are included. The peak position for same-side unlike-sign pairs remains at the same approximate momentum for peripheral to mid-central collisions. However, for more-central collisions the same-side peak separates into two peaks. The centrality dependence of these data will be compared with that of $p_t$-integral 2D angular correlations [3]. The transverse momentum dependence of the same-side angular correlation structures will also be presented. Possible mechanisms for the observed structures will be discussed and predictions from several models will be presented to test agreement with data. [1] STAR Collaboration, J. Adams, et al., J. Phys. G 34 799 (2007). [2] L. Ray (2010). Workshop on Critical Examination of RHIC Paradigms [Online]. Available: http://www.rhip.utexas.edu/projects/Star/paradigms/Ray.ppt [2012,March 23] [3] M Daugherity (for the STAR Collaboration), J. Phys. G: Nucl. Part.Phys. 35 104090 (2008).Speaker: Elizabeth Oldag (UT Austin, STAR Collaboration)
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Unfolding of ALICE tracking and calorimeter response to fully reconstructed jets in Pb-Pb collisions 2hObservables involving fully reconstructed jets provide access to key properties of the quark-gluon plasma via partonic energy loss. In order to obtain the inclusive transverse momentum distribution of fully reconstructed jets using the ALICE tracking detectors and electromagnetic calorimeter, the smearing effect of non-ideal detector responses must be understood and corrected. The procedure for assessing these response effects will be explained. In addition, the unfolding techniques that are applied to measured distributions are described, and the results and their uncertainties will be presented.Speaker: Andrew Marshall Adare (Yale University (US))
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Unraveling Cold Nuclear Matter Effects with the sPHENIX Forward Upgrade 2hStudies of proton (deuteron) - nucleus collisions allow for the detailed examination of cold nuclear matter effects (including gluon saturation, initial state parton energy loss, nuclear break up and others), while also providing a crucial baseline for nucleus-nucleus collisions with additional hot quark-gluon plasma effects. The PHENIX experiment is planning an ambitious upgrade program referred to as sPHENIX that includes a mid-rapidity solenoid with full calorimetry coverage. In addition, the sPHENIX planning includes extended forward rapidity coverage. In this presentation, we detail two example physics observables at forward rapidity that are key to unraveling these cold nuclear matter effects. The first is the extension of heavy quarkonia measurements to more forward rapidities where the effects of gluon saturation and initial state parton energy loss are predicted to be enhanced. The second is the determination of transverse momentum dependent (TMD) gluon parton distributions in nuclei. Recent theoretical progress indicates that while TMD factorization is broken, it is recovered at low-x and makes a direct connection to Color Glass Condensate calculations. These distributions will be measured using direct photon-jet and jet-jet correlations - a primary design requirement for the sPHENIX forward update plan.Speaker: Prof. Seto Richard (University of California, Riverside)
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Upsilon suppression in PbPb collisions at LHC energies 2hWe suggest that the combined effect of screening, gluon-induced dissociation, Landau damping, and reduced feed-down explains most of the suppression of Y states that has been observed by CMS [1] in PbPb relative to pp collisions at sqrt(s_NN) = 2.76 TeV at the CERN LHC. The suppression is thus a clear, albeit indirect, indication for the presence of a qgp. In particular, we calculate the suppression of both the Y(1S) ground state in the quark-gluon plasma in minimum-bias PbPb collisions, and of the Y(2S + 3S) states relative to the ground state. In a major extension of our schematic phenomenological approach presented in [2], we now explicitly consider the time dependence with transverse and longitudinal expansion, and the effect of Landau damping [3] on the widths of the states, in addition to gluodissociation. The effect of Landau damping of the Y(nS) and Chi_b(nP) states is computed from a complex potential, and is found to be of the same order of magnitude as the gluon-induced dissociation [2] for the 1S state at the temperatures that are relevant at LHC. The gluodissociation is treated explicitly for all five states considered here (1S, 2S, 3S, 1P and 2P), including the influence of the confining string contribution on the dissociation rates. As compared to pp collisions at the same energy, the feed-down cascade leading to the Y(1S) ground state is drastically modified due to the substantial suppression of the excited states through screening, damping and gluodissociation. The 1S ground state remains very stable with respect to screening, its suppression is essentially due to damping, gluodissociation and reduced feed-down. Our results are presented for different Y formation times and qgp lifetimes. For reasonable plasma temperatures at Y formation time, we obtain good agreement with the CMS data for the Y(1S) suppression factor, but less suppression than is needed for the measured [1] ratio Y(2S + 3S)/ Y(1S) - which requires, however, better statistics. Should the result persist in the 2011 data, it is likely that additional suppression mechanisms are at work. References [1] S. Chatrchyan et al., CMS Collab., Phys. Rev. Lett. 107, 052302 (2011), and contribution to this conference [2] F. Brezinski and G. Wolschin, Phys. Lett. B 707, 534 (2012) [3] M. Strickland, Phys. Rev. Lett. 107, 132301 (2011)Speaker: Georg Wolschin (Heidelberg University)
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Using CMBR tools to study flow anisotropies in relativistic heavy ion collisions 2hWe study the interesting similarities between the physics of cosmic microwave background radiation anisotropies and the flow anisotropies in relativistic heavy ion collision experiments. Further we explore how the techniques in CMBR analysis could be utilized in studying the flow anisotropies in RHICE. We argue that the initial state fluctuations of the matter formed in heavy ion collisions have similar properties as the fluctuations in the early universe generated by the inflaton field, and by studying the flow coeffecients ( a plot of v_n vs. n) we can obtain valuable information about the nature and evolution of these fluctuations. We also study the effect of magnetic field on flow. In the presence of magnetic field plasma develops three acoustic modes. It is known in literature that this distorts the CMB acoustic peaks. We show that flow coefficients in relativistic heavy ion collisions can be significantly affected by these effects where a a strong magnetic field is known to be present in the initial stages (of non-central collisions) and is expected to survive due to strong induced fields in the conducting plasma. This raises the possibility whether a larger value of $\eta/s$ can be accommodated by RHIC data. We also show that flow anisotropies in relativistic heavy-ion collisions can be analyzed using a certain technique of shape analysis of excursion sets recently proposed by us for CMBR fluctuations to investigate anisotropic expansion history of the universe. The technique analyzes shapes (sizes) of patches above (below) certain threshold value for transverse energy/particle number fluctuations (the excursion sets) as a function of the azimuthal angle and rapidity. This provides an alternative way to identify the event plane in an event.Speaker: Ms P S Saumia (Institute of Physics)
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Virtual photons and rare strange probes in resonance matter 2hThe HADES experiment, installed at the Helmholtzzentrum für Schwerionenforschung (GSI) accelerator facility in Darmstadt, investigates dielectron emission and strangeness production in various collision systems (p+p, p+n, p+A and A+A) in the 1-3.5 AGeV regime. The observed low-mass dielectron and Ξ- enhancement in intermediate heavy-ion collisions indicates the onset of medium effects, on the one hand, and underlines the importance of a solid knowledge of contributions of baryon resonances on the other hand. The latter turned out to be of eminent importance for the interpretation of the spectral shape of the ρ meson already in elementary data and moreover for the extraction of additional medium effects in p+A and A+A collisions. Such a knowledge is gained by the analysis of exclusive hadronic channels in elementary reactions. In this contribution, we summarize the findings of HADES and implications, with a special emphasis on the baryon resonance contributions.Speaker: Mr Manuel Lorenz (Goethe University Frankfurt)
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Viscous Corrections to Hadron Phase Space Distributions from linearized Boltzmann Equation 2hComparing hydrodynamic simulations to data inevitably requires the conversion of the fluid to particles. This conversion is ambiguous for viscous fluids as an infinite class of phase space densities can produce the same hydrodynamic variables. We compute self-consistent phase space corrections for hadron species by solving the linearized Boltzmann equation. These distribution functions are then used in the Cooper-Frye formalism to calculate observables such as spectra and anisotropic flow coefficients. The results are contrasted with those obtained using the ad hoc species-independent quadratic momentum dependence (Grad ansatz) that is typically assumed in the literature.Speaker: Mr Zachary Wolff (Purdue University)
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vSPheRIO: A New Event-by-Event Viscous Hydrodynamical Code 2hvSPheRIO is a new second order viscous hydrodynamic code for ultrarelativistic heavy ion collisions that can be consistently run on an event-by-event basis. This code, which is the viscous generalization of the well known SPheRIO code \cite{Aguiar:2000hw}, solves second order viscous hydrodynamic equations. In this talk, we use vSPheRIO to investigate the time evolution of a boost invariant QGP, with a realistic equation of state \cite{Huovinen:2009yb}, and temperature dependent $\eta/s$ and $\zeta/s$ \cite{NoronhaHostler:2008ju}. Results for the anisotropic flow coefficients $v_2$ to $v_5$ obtained within this setup are compared to other viscous hydrodynamic calculations that involved constant $\eta/s$ and $\zeta/s$ ratios \cite{Schenke:2011bn}. %\cite{Aguiar:2000hw} \bibitem{Aguiar:2000hw} C.~E.~Aguiar, T.~Kodama, T.~Osada and Y.~Hama, %``Smoothed particle hydrodynamics for relativistic heavy ion collisions,'' J.\ Phys.\ G G {\bf 27}, 75 (2001) [hep-ph/0006239]; Y.~Hama, T.~Kodama and O.~Socolowski, Jr., %``Topics on hydrodynamic model of nucleus-nucleus collisions,'' Braz.\ J.\ Phys.\ {\bf 35}, 24 (2005) [hep-ph/0407264]; R.~Andrade, F.~Grassi, Y.~Hama, T.~Kodama and O.~Socolowski, Jr., %``On the necessity to include event-by-event fluctuations in experimental evaluation of elliptical flow,'' Phys.\ Rev.\ Lett.\ {\bf 97}, 202302 (2006) [nucl-th/0608067]. %\cite{Huovinen:2009yb} \bibitem{Huovinen:2009yb} P.~Huovinen and P.~Petreczky, %``QCD Equation of State and Hadron Resonance Gas,'' Nucl.\ Phys.\ A {\bf 837}, 26 (2010) [arXiv:0912.2541 [hep-ph]]. %%CITATION = ARXIV:0912.2541;%% %\cite{NoronhaHostler:2008ju} \bibitem{NoronhaHostler:2008ju} J.~Noronha-Hostler, J.~Noronha and C.~Greiner, %``Transport Coefficients of Hadronic Matter near T(c),'' Phys.\ Rev.\ Lett.\ {\bf 103}, 172302 (2009); H.~Niemi, G.~S.~Denicol, P.~Huovinen, E.~Molnar and D.~H.~Rischke, %``Influence of the shear viscosity of the quark-gluon plasma on elliptic flow in ultrarelativistic heavy-ion collisions,'' Phys.\ Rev.\ Lett.\ {\bf 106}, 212302 (2011); G.~S.~Denicol, T.~Kodama, T.~Koide and P.~Mota, %``Effect of bulk viscosity on Elliptic Flow near QCD phase transition,'' Phys.\ Rev.\ C {\bf 80}, 064901 (2009). %\cite{Schenke:2011bn} \bibitem{Schenke:2011bn} B.~Schenke, S.~Jeon and C.~Gale, %``Higher flow harmonics from (3+1)D event-by-event viscous hydrodynamics,'' Phys.\ Rev.\ C {\bf 85}, 024901 (2012) [arXiv:1109.6289 [hep-ph]]. %%CITATION = ARXIV:1109.6289;%%Speaker: Jacquelyn Noronha-Hostler (U)
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Why the formula $\mean{dN_{ch}^{AA}/d\eta}=\mean{dN_{ch}^{pp}/d\eta} [x N_{part}/2 +(1-x) N_{coll}]$ should be deprecated 2h\bc {\large \bf{ Why the formula\\ $\mean{dN_{\rm ch}^{AA}/d\eta}=\mean{dN_{\rm ch}^{pp}/d\eta} [x N_{\rm part}/2 +(1-x) N_{\rm coll}]$\\ should be deprecated}} \bs Abstract for Quark Matter 2012 poster \bs \underline{Michael J. Tannenbaum}~$^{a)}$ $^{a)}$ Physics Department, Brookhaven National Laboratory, Upton, NY 11973-5000, USA The fact that the multiplicity density in A+A collisions increases faster than the number of participants has led to the popular formula $\mean{dN_{\rm ch}^{AA}/d\eta}=\mean{dN_{\rm ch}^{pp}/d\eta} [x N_{\rm part}/2 +(1-x) N_{\rm coll}]$ with the implication that point-like hard-scattering contributes to the total charge multiplicity or $\sum E_T$ distributions. For $\sqrt{s}=630$ GeV $\bar{p}-p$ collisions, the UA2 collaboration~\cite{UA2PLB165} measured that the hard-scattering component of $\sum E_T$ distributions only becomes apparent at the level of $\sim 1/500$ the total cross-section, clearly indicating that the contribution of hard-process to the multiplicity and $\sum E_T$ distributions is negligible. The universal behavior of $\mean{dN_{\rm ch}^{AA}/(0.5N_{\rm part}d\eta)}$ as a function of $N_{\rm part}$ at RHIC and LHC over the range $7\leq \sqrt{s_{NN}}\leq 2760$ GeV, in spite of the dramatic increase in the ratio of $N_{\rm coll}/N_{\rm part}$ due to the increasing N-N interaction cross section, is another indication. Finally, an $E_T$ distribution which satisfies the popular formula for $\mean{dN_{\rm ch}^{AA}/d\eta}$ will be demonstrated and shown to look nothing like any measured $\sum E_T$ distribution. A more reasonable nuclear geometrical description has been given previously~\cite{Voloshin,De,Nouicer} and will be tested with recent data. \begin{thebibliography}{9} \bibitem{UA2PLB165} UA2 Collab., \Journal{\PLB}{165}{441-448}{1985}. \bibitem{Voloshin} S.~Eremin and S.~Voloshin, \Journal{\PRC}{67}{064905}{2003}. \bibitem{De} B.~De and S.~Bhattacharyya, \Journal{\PRC}{71}{024903}{2005}. \bibitem{Nouicer} R. Nouicer, \Journal{\EPJC}{49}{281}{2007}. \end{thebibliography} \end{document}Speaker: Michael Tannenbaum (Brookhaven National Laboratory (US))
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Yet stronger enhancement of Xi production at SIS 2hWe calculate the expectation of Xi yields in nuclear collisions at SIS energies for the case that the produces strangeness is distributed statistically over S<0 species. By taking into account that cascades are produced only in events where two kaons are produced we obtain theoretical value which is about 1/2 of that reported in previous calculations. Even possible modifications of hadron properties in baryon-rich medium do not reconcile model calculations with the data. We point out the necessity of a non-equilibrium production process in order to interpret the measured values. We note that the developed statistical model is applicable also to other species with strangeness or charm bigger than 1.Speaker: Boris Tomasik (Univerzita Mateja Bela (SK))
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Plenary VA: Exploring the QCD Phase Diagram (Chair: P. Braun-Munzinger) Regency 2/3
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Coffee Break 30m Bird Cage & Regency Gallery
Bird Cage & Regency Gallery
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Plenary VB: Future Developments I (Chair: C. Greiner) Regency 2/3
Regency 2/3
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Lunch 1h 20m Blue Room
Blue Room
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Parallel 6A: Heavy Flavor & Quarkonia (Chair Y. Akiba) Ambassador
Ambassador
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D meson nuclear modification factors in Pb–Pb collisions at 2.76 TeV with the ALICE detector 20mThe properties of the hot and dense QCD medium formed in ultra-relativistic heavy ion collisions, as well as the mechanism of in-medium partonic energy loss, can be accessed via the measurement of the nuclear modification factor of particle production. The measurement of D meson production provides key tests of parton energy-loss models, which predict that charm quarks should experience less in-medium energy loss than light quarks and gluons. The ALICE experiment has measured the production of prompt D0, D+ and D*+ mesons in pp and Pb-Pb collisions at the LHC at sqrt(s) = 7 and 2.76 TeV and at sqrt(s_{NN}) = 2.76 TeV, respectively, via the exclusive reconstruction of their hadronic decay. The p_t -differential production yields in the range 2 < pt < 16 GeV/c at central rapidity, |y| < 0.5, were used to calculate the nuclear modification factor. A suppression of a factor 3–4 for transverse momenta larger than 5 GeV/c in the 20% most central collisions was observed. The suppression is reduced in peripheral collisions. Preliminary results in an extended p_t -range, using the data sample collected during the 2011 Pb-Pb run, will be shown.Speaker: Alessandro Grelli (University of Utrecht (NL))
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Open charm hadron production in p+p and Au+Au collisions at STAR 20mIn relativistic heavy ion collisions at RHIC, heavy quarks are expected to be created from initial hard scatterings. Their large masses are not easily affected by the strong interaction with QCD medium, thus they carry clean information from the system at early stage. The interaction between heavy quarks and the medium is sensitive to the medium dynamics, therefore heavy quarks are suggested as an ideal probe to quantify the properties of the strongly interacting QCD matter. In this talk, we will present the STAR results of open charm hadron production at mid-rapidity in $p+p$ and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Open charm mesons were reconstructed directly via hadronic decay channels with daughter particles identified by TPC and TOF detectors. With abundant statistics of Au+Au collisions collected by STAR in the year 2010 and 2011, the D-meson is measured at $p_T$ from 0.2 to 8 GeV in minimum bias Au+Au collisions. The centrality dependence of D-meson $p_T$ spectra as well as the nuclear modification factor will be presented. A first measurement of the $D^{0}$ elliptic flow in 200 GeV Au+Au collisions will be reported. These measurements are compared to theoretical model calculations and physics implications will be discussed. Finally, we will discuss the open charm hadron measurement in $\sqrt{s}=500$ GeV $p+p$ collisions to study the energy dependence of charm production.Speaker: Mr David Tlusty (PhD student)
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Measurement of the D meson elliptic flow in Pb-Pb collisions at 2.76 TeV with ALICE. 20mThe ALICE experiment at the LHC studies Pb-Pb and pp collisions with the aim of investigating the properties of the high-density state of strongly-interacting matter, expected to be produced in Pb-Pb collisions. Heavy quarks are sensitive probes to test the medium properties, since they are formed at shorter time scale with respect to the deconfined state. The elliptic flow v2 of D meson compared to that of light hadrons is expected to bring insights into the degree of thermalization of charm quarks within the quark-gluon plasma. D meson have been reconstructed in their hadronic decay channels (D0 --> K-pi+, D+-->K-pi+pi+, D*+-->D0pi+), in the central rapidity region in Pb-Pb collisions at sqrt{s_NN}=2.76 TeV, with data collected in the 2011 run. The measurement of the D meson elliptic flow in semi-central Pb-Pb collisions will be presented.Speaker: Davide Caffarri (Universita e INFN (IT))
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15:00
Probing Hot and Dense Matter with c and b Measurements with PHENIX VTX Tracker 20mWell-calibrated penetrating probes are essential for investigating the properties of the hot, dense medium created in high-energy nuclear collisions at RHIC. One such probe are hadrons which carry heavy flavor (charm and bottom quarks). They are a powerful tool for studying the medium because they are generated early in the reaction and subsequently propagate through the created matter. Two very striking results have already been seen for open heavy flavor from the PHENIX experiment via the measurement of electrons from semi-leptonic decays of hadrons carrying charm or bottom quarks. First, heavy mesons, despite their large mass, exhibit a suppression at high transverse momentum compared to that expected from p+p interactions. This suppression is found to be similar to that of light mesons which implies a substantial energy loss of fast heavy quarks while traversing the medium. Secondly, an elliptic flow is observed for heavy mesons which is comparable to that of light mesons like pions. This imply that the same heavy quarks are in fact sensitive to the pressure gradients driving hydrodynamic flow—giving new insight into the strongly coupled nature of the QGP fluid at these temperatures. In these early results, PHENIX was not able to distinguish electrons from c and b independently. In order to understand these medium effects in more detail it is imperative to directly measure the nuclear modification and the flow of c and b separately. With the addition of the silicon vertex tracker, VTX, to PHENIX these direct measurements are now possible. We will present the latest PHENIX measurements of single electrons from beauty and charm decays, emphasizing the flow, v2, and nuclear modification factor, RAA, including the latest progress with the VTX.Speaker: Dr Rachid Nouicer (Brookhaven National Laboratory (BNL))
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15:20
Heavy quark evolution and flow in hot and dense medium 20mHeavy quarks serve as valuable probes of the transport properties of the quark-gluon plasma created in relativistic heavy-ion collisions. Within the framework of a Langevin approach, coupled to a realistic 3D hydrodynamic calculation of the medium, we study the heavy quark energy loss due to quasi-elastic multiple scatterings. We extend this algorithm to include medium-induced gluon radiation in hot and dense nuclear matter. Within this new and improved approach, we perform a detailed analysis of various ingredients affecting the final heavy flavor spectra and elliptic flow, such as the coupling strength between heavy quarks and the medium, the medium's geometric anisotropy and its flow profile, and the relative contributions from charm and bottom quarks. We demonstrate the consistency between these properties and our previous study of the thermalization behavior of heavy quarks inside the QGP. We also present simulations of heavy flavor quenching and elliptic flow, including both collisional and radiative energy loss, for RHIC and LHC experiments.Speaker: Shanshan Cao (Duke University)
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Suppression of open bottom at high pT via non-prompt J/psi decays in PbPb collisions at 2.76 TeV with CMS 20mMeasurements of the nuclear modification factor of mesons with open heavy flavor content in PbPb collisions at sqrt(sNN) = 2.76 TeV from the CMS experiment will be presented. These modification factors provide stringent constraints on the theoretical models of heavy quark energy loss. Until recently only indirect measurements of this effect existed, through single electrons from semileptonic open heavy-flavor decays. The importance of an unambiguous measurement of open bottom flavor is driven by the lack of knowledge regarding key features of the dynamics of parton energy loss in the QGP, such as its color-charge and parton-mass dependencies and the relative role of radiative and collisional energy loss. CMS is the first, and so far only, experiment to measure the nuclear modification factor of B hadrons, identified via their decays into J/psi displaced from the primary collision vertex. First results have shown that B hadrons are strongly suppressed in PbPb collisions at a level comparable to open charm. New results on the centrality dependence of RAA and the first measurement of the azimuthal anisotropy of non-prompt J/psi will be presented, based on the full 2011 PbPb data sample corresponding to an integrated luminosity of 150/ub.Speaker: Mihee Jo (Korea University (KR))
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Parallel 6B: Exploring the QCD Phase Diagram (Chair K. Rajagopal) Regency 2/3
Regency 2/3
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A No-Go Theorem for Critical Phenomena in QCD at finite temperature and density 20mWe discuss the phase diagram of quantum chromodynamics (QCD) at finite T and finite quark chemical potential \mu. In particular, we focus on the QCD critical point(s), which has attracted considerable attention in its search at the relativistic heavy ion collision experiments. However, not only the location, but even the existence has not yet been settled. In this talk, we show that the critical points are forbidden in flavor-symmetric QCD at finite \mu for any nonzero quark mass, as long as the coordinate (T, \mu) is outside the pion condensed phase in the corresponding phase diagram of QCD at finite isospin chemical potential \mu_I = 2\mu, if the two and higher quark loops are negligible in the thermodynamic potential and the correlation functions (The large-Nc QCD naturally satisfies this condition). Reference Y. Hidaka and N. Yamamoto, Phys. Rev. Lett.108, 121601 (2012).Speaker: Dr Yoshimasa Hidaka (RIKEN Nishina Center)
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QCD Critical Point : Marching towards continuum 20mWe simulate QCD with two light dynamical quarks on a 32^3 X 8 lattice by tuning the current quark mass such that the Goldstone pion mass is about 230 MeV. Earlier results of our Mumbai group corresponded to the same physical parameters but were on coarser lattices at respectively 1.33 times and twice the lattice cut-off (a) compared to these simulations, thus permitting us a march towards the continuum limit. Employing the Taylor expansion method we had proposed earlier to estimate the radius of convergence of the series for the baryonic susceptibility, and using up to eight order terms, we attempt to zoom in on the QCD critical pointSpeaker: Rajiv V Gavai (Tata Institute, Mumbai, India)
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Influence of a Critical Point on Hydrodynamic Fluctuations in Heavy Ion Collisions 20mHydrodynamic fluctuations are inherent in any small space-time varying system. They may be significantly impacted by the presence of a critical point in the QCD equation of state during the expansion phase of a heavy ion collision. Simple models are studied to gain insight into the essential physics. This study suggests which observables are most sensitive to a critical point, although much more sophisticated numerical simulations need to be done to compare directly with experimental data.Speaker: Joseph Kapusta (University of Minnesota (US))
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Centrality dependence of freeze-out parameters from the Beam Energy Scan at STAR 20mThe RHIC Beam Energy Scan (BES) program aims to study the QCD phase diagram. The main focus is to search for signals of the hypothesized critical point and the onset of the quark-hadron phase transition. The BES program covers a large part of the QCD phase diagram ($T$ vs.$mu_{B}$). With its uniform acceptance and excellent particle identification, STAR has collected large event samples in the $mu_{B}$ range 100-400 MeV. This makes it possible to study, in addition to the energy dependence, the centrality dependence of freeze-out parameters such as temperature, baryon chemical potential, and radial collectivity. We present the first results on the centrality dependence of freeze-out parameters in Au+Au collisions at $\sqrt{s_{NN}} =$ 7.7, 11.5 and 39 GeV from the STAR experiment. The chemical freeze-out conditions are obtained by comparing the measured particle ratios at midrapidity (involving $\pi^{\pm}$, $K^{\pm}$, $K_{s}$, $p(\bar{p})$, $\phi$, $\Lambda$, $\Xi$, and $\Omega$) to those from the statistical-thermal model calculations (THERMUS). We observe a clear centrality dependence in both $T$ and $mu_{B}$ values at the lower beam energies (11.5 and 7.7 GeV). Whereas no such dependence is observed for higher beam energies (200 - 62.4 GeV). The implications of including multi-strange hadrons and choosing different ensembles (Grand canonical versus Strangeness canonical) in THERMUS model on the $T$ and $mu_{B}$ values will be discussed. The kinetic freeze-out parameters are obtained by fitting the invariant yields of the produced particles ($\pi^{\pm}$, $K^{\pm}$, and $p(\bar{p})$), as a function of transverse momentum, to the Blast-Wave and Tsallis models. The kinetic freeze-out temperature and the radial collectivity which shows an anti-correlation at all the energies studied will be presented.Speaker: SABITA DAS (I)
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Event anisotropy v_2 in Au+Au collisions at 7.7 - 62.4 GeV with STAR 20mThe exploration of the QCD phase diagram in the region of a possible phase transition between the Quark Gluon Plasma (QGP) and the hadron gas phase is one of the main goals of the RHIC Beam Energy Scan(BES). One of the most important observables from high-energy nuclear collisions to study the early evolution of the expanding system is the elliptic flow $v_{2}$. At the top RHIC energy, $\sqrt{s_{NN}}$ = 200 GeV, the number-of-constituent quark (NCQ) scaling of $v_{2}(p_{T})$ is interpreted as a signature of deconfinement and the formation of the QGP phase. A disappearance of the NCQ scaling is expected for a pure hadronic system at low beam energies. Hence it is a necessary signature to identify the phase transition. We present the $v_2$ measurement at midrapidity from Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV for inclusive charged hadrons, light nuclei ($d$, $\bar{d}$) and identified hadrons ($\pi^{\pm}$, $K^{\pm}$, $K_{S}^{0}$, $p$, $\bar{p}$, $\phi$, $\Lambda$, $\bar{\Lambda}$, $\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$) up to 4 GeV/$c$ in $p_{T}$. The beam energy and centrality dependence of charged hadron $v_2$ are presented with comparison to higher energies at RHIC and LHC. The identified hadron $v_{2}$ are used to discuss the NCQ scaling for different beam energies. Significant difference in $v_{2}(p_{T})$ is observed between particles and corresponding anti-particles for $\sqrt{s_{NN}} <$ 39 GeV. These differences are more pronounced for baryons compared to mesons and they increase with decreasing energy and increasing centrality. The $v_{2}$ difference between particles and anti-particles shows an almost linear dependency with the baryon chemical potential $\mu_{B}$. The transport model calculations of UrQMD and AMPT models are compared with the experimental data.Speaker: Shusu Shi (CCNU)
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Dynamic enhancement of event-by-event fluctuations at the critical point and domain formation at the first order phase transition of QCD 20mStrong fluctuations in observables are believed to provide decisive signals for identifying phase transitions of QCD in relativistic heavy-ion collisions. To study this possibility under realistic conditions of the expansion and the cooling of the fireball we performed dynamic simulations within our approach of nonequilibrium chiral fluid dynamics. Based on an effective phase transition model, chiral fields and their fluctuations propagate explicitly within a medium that expands fluid dynamically. The interaction between the fields and the fluid leads to dissipation and noise, which in turn affect the chiral propagation. In this talk we present the consequences of this coupled dynamics for different phase transition scenarios. In the case of a first order phase transition we observe the development of a highly supercooled state. This leads to the dynamic formation and decay of domains of the chirally-symmetric phase in a chirally-broken environment and can be seen in single event studies. At the critical point, due to large relaxation times, we find that critical slowing down weakens the critical phenomena. However, for the first time we are able to demonstrate in a dynamic and realistic study the basic features of a critical point: the growth of the correlation length and the enhancement of event-by-event fluctuations of the sigma field. It is, therefore, expected that both, the first order phase transition and the critical point develop their characteristic signals in heavy-ion collisions.Speaker: Dr Marlene Nahrgang
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Parallel 6C: New Experimental Developments (Chair J. Stroth) Palladian
Palladian
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14:00
STAR Upgrade Plan for the Coming Decade 20mThe STAR Collaboration is scheduled to complete the Heavy Flavor Tracker (HFT) and the Muon Telescope Detector (MTD) upgrades by 2014. These detectors will greatly enhance the STAR physics capability to measure heavy quark collectivity and correlations using topologically reconstructed charm hadrons and heavy quark decay e-muon correlations. In addition, measurements of the quarkonium muon decay channels will enable us to separate Upsilon 1S from 2S and 3S states in p+p and A+A collisions. STAR has also embarked on an upgrade plan to extend the measurement capabilities for jets, electron/photon and leading particles in the forward rapidity region in the coming decade. Planned detector upgrades include tracking detectors for charged particles, electro-magnetic and hadronic calorimeters and particle identification detector in the forward direction. We will present physics motivations, status of detector R&D and design considerations for the forward measurements focusing on p+p/p+A and polarized p+p collisions. The STAR detector system will be in a unique position to make important measurements for e+p and e+A physics program during the early phase of the eRHIC era. Our physics considerations and possible detector evolution towards an eSTAR program will also be discussed.Speaker: Prof. Huan Huang (UCLA, For the STAR Collaboration)
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The sPHENIX Barrel Upgrade: Jet Physics and Beyond 20mThe past decade of heavy ion physics at RHIC has produced many surprising discoveries and puzzles. Currently the experiments at the LHC are providing a first look at things to come: a burgeoning program for studying the Quark Gluon Plasma with reconstructed jets. The PHENIX collaboration is in the process of developing a long term plan involving a series of aggressive upgrades designed to expand the physics capabilities and make use of the full enhanced luminosity at RHIC. With increased coverage and the addition of hadronic calorimetry, we will demonstrate that the sPHENIX upgrade will be well positioned to provide a broad and exciting program of jet probe measurements. Sampling 50 billion Au+Au events annually, we will collect 10 million jets with transverse energy above 20 GeV and 100 thousand jets above 40 GeV. With the addition of tracking layers and an EM preshower, a crucial program of upsilon measurements, as well as neutral pion and direct photon measurements with a 40 GeV/c reach, can be made in a flexible accelerator facility capable of providing a diverse range of collision systems across many beam energies. And, ultimately, the sPHENIX detector will provide the base for staging a future electron-ion collider detector at eRHIC.Speaker: John Haggerty (Brookhaven National Laboratory)
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Upgrade of the ALICE Experiment 20mAt the LHC the ALICE experiment is taking data in p+p, p+A and A+A collisions, which is providing unique insights on strongly interacting matter at an unprecedented energy density. Many important questions in heavy-ion physics will, however, remain unanswered in this first running period up to 2017. Only by increasing the luminosity beyond 10^27 and exploiting recent advances in technology ALICE will be able to address the new and remaining scientific challenges. ALICE is therefore setting up a program of detector upgrades, to be installed in the LHC shutdown planned for 2018. The planned upgrades will give access to otherwise unreachable rare processes, in particular observables involving heavy quarks and quarkonia at low transverse momentum, but also low-mass dileptons, selected topics in photon-jet physics with identified particles, and the search for heavy nuclear states. The potential of unique low-x measurements is also investigated. We will discuss examples of the scientific frontiers and the strategy of ALICE to address them. We will include an overview of the specific upgrade projects under study for the ALICE experiment.Speaker: Thomas Peitzmann (University of Utrecht (NL))
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The sPHENIX Forward Upgrade 20mDuring 12 years of operations, PHENIX has discovered a strongly coupled QGP and studied many of its basic properties, examined effects in cold nuclear matter, measured the gluon helicity structure of the proton, and probed the proton transverse spin structure. PHENIX is planning a large upgrade for the next decade, sPHENIX, to answer many of the questions spurred by our discoveries during the last decade. This sPHENIX upgrade includes replacing the central arm spectrometers with an open geometry solenoid surrounded by electromagnetic and hadronic calorimetry. With this new open geometry, we plan to upgrade our detector at forward rapidities with additional calorimetry and tracking. The larger acceptance will improve our access to low-x distributions in heavy nuclei, extend our measurements of quarkonia in p+p, d+A, and A+A to more forward rapidities, and allow for measurements away from the Bjorken plateau expanding the study of the high energy heavy ion environment. In addition to heavy ion and cold nuclear matter measurements, the envisioned forward rapidity upgrade will allow for a more systematic approach to understanding the large transverse spin measurements seen at RHIC as well as serve as the baseline detector for a future eRHIC detector, ePHENIX.Speaker: Joseph Seele (RBRC)
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The ALICE Inner Tracking System Upgrade 20mThe major long-term goal of the ALICE experiment at the LHC is to provide precision measurements of the properties of the Quark-Gluon Plasma, the state of deconfined matter produced in high-energy heavy-ion collisions. Experiments towards the characterisation of strongly interacting matter at high density will need to focus on rare probes and the study of their collective properties and hadronization, particularly at soft momentum scales. Such considerations have motivated the development of a comprehensive upgrade strategy for ALICE to provide high rate capability (50 kHz for Pb-Pb collisions) in a near minimum bias mode by building a new Inner Tracking System and by modifying all major ALICE detectors to provide a fully pipelined read-out. This implies also a major upgrade of the data acquisition and high level trigger system. Further details of the overall ALICE upgrade strategy are described in [1]. This contribution will describe the proposed approach to upgrading the Inner Tracking System (ITS) in order to both comply with the new requirements set by the ALICE global upgrade strategy and to dramatically improve the performance for heavy-flavour detection. The ITS Upgrade will have greatly improved features in terms of: determination of the distance of closest approach (dca) to the primary vertex, standalone tracking efficiency at low pt, momentum resolution and readout capabilities. These improvements are possible as a consequence of the spectacular progress made in the field of imaging sensors over the last ten years as well as the possibility to install a smaller radius beampipe. Moreover a tracker with the above features, in particular a high standalone tracking efficiency, creates an opportunity to perform, in combination with the TRD and TOF detectors, online event selection on the basis of topological and PID criteria. Such a new silicon tracker will allow ALICE to measure charm and beauty production in Pb-Pb collisions with sufficient statistical accuracy down to very low transverse momentum, measure charm baryons and perform exclusive measurements of beauty production. A comprehensive description of the ITS Upgrade can be found in the recent Conceptual Design Report [2]. [1] Upgrade Strategy for ALICE at High Rate, CERN-LHCC-2012-04. [2] Conceptual Design Report for the Upgrade of the ALICE ITS, CERN-LHCC-2012-05.Speaker: Roy Crawford Lemmon (Engin. & Phys. Sci. Research Coun. (GB))
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The Compressed Baryonic Matter Experiment at FAIR - physics at SIS-100 and SIS-300 20mThe Compressed Baryonic Matter (CBM) Experiment will explore the phase diagram of strongly interacting matter in the region of high net baryon densities. The experiment is laid out to process nuclear collisions at rates up to 10 MHz, the highest in the field. A unique wide spectrum of observables will be accessible, including rarest probes like hadrons containing charm quarks, or multi-strange hyperons. The realization of the full CBM physics programme requires heavy-ion beams of energies up to 45 GeV/nucleon. Those will be delivered by the SIS-300 synchrotron at the completed FAIR accelerator complex. Parts of the research programme can already be addressed with the SIS-100 synchrotron installed in the same machine tunnel for the start phase of FAIR. The initial energy range of up to 11 GeV/nucleon for heavy nuclei, 14 GeV/nucleon for light nuclei, and 29 GeV for protons, allows addressing the equation of state of compressed nuclear matter, the properties of hadrons in a dense medium, the production and propagation of charm near the production threshold, and exploring the third, strange dimension of the nuclide chart. In the presentation we discuss the CBM physics programmes and the detector setup with focus on the first years of operation at FAIR, along with an outline of the recently begun construction of the accelerator facility.Speaker: Johann Heuser (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
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Parallel 6D: Correlations & Fluctuations (Chair O. Evdokimov) Diplomat
Diplomat
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Anisotropic flow of identified particles in Pb-Pb collisions at 2.76 TeV measured with ALICE at the LHC 20mThe anisotropic flow of identified particles is an important observable to probe the freeze-out properties, the parton energy loss and the partonic phase of the system created in heavy-ion collisions. We report on the elliptic and triangular flow measurements for a number of identified particles such as charged pions, kaons and (anti-)protons, as well as K0s , Λ/anti-Λ, Ξ, and Ω. The results are reported at mid-rapidity, |η| < 0.8, over a wide range of transverse momenta, 0.2 < pt < 16 GeV/c, for Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV recorded by ALICE at the LHC. The mass splitting and the scaling properties of the elliptic and triangular flow with the number of constituent quarks and the particle transverse mass are studied as a function of collision centrality. The results are compared to RHIC measurements and to hydrodynamic model predictions.Speaker: Francesco Noferini (Universita e INFN (IT))
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Elliptic azimuthal anisotropy of charged hadrons and neutral pions in PbPb collisions at 2.76 TeV with CMS 20mThe elliptic flow anisotropies of charged particles and neutral pions (pi0s) have been measured by the CMS collaboration for PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV. The second Fourier components of the anisotropic azimuthal distribution are obtained using an event-plane technique for pi0s and four different analysis techniques for charged particles: event plane, two- and four-particle cumulants, and Lee-Yang Zeros. These techniques have different sensitivities to non-flow and flow fluctuation effects and their comparison helps disentangle hydrodynamic flow, initial state fluctuations and non-flow correlations. The results are presented as a function of pT, pseudorapidity, and centrality. A comparison of the CMS measurements of v2(pT) from pi0 mesons and inclusive charged particles reveals a systematic difference in the range of pT = 2.5 ~ 5 GeV/c, with the neutral pion anisotropies being weaker than those observed for inclusive charged particles. This difference indicates a particle-species dependence in the azimuthal anisotropy at the LHC. New measurements of correlations associated with mixed harmonics for charged particles are explored and discussed in terms of participant fluctuations. A systematic comparison of the LHC results to lower energy observations will also be presented.Speaker: Eric Andrew Appelt (Vanderbilt University (US))
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Measurements of flow harmonics with the cumulant method from the ATLAS experiment 20mThe measurement of the azimuthal anisotropy of charged particles obtained with the multi-particle correlations method will be presented and compared to the results obtained with the event plane method for Pb+Pb collisions at 2.76 TeV from the ATLAS experiment. Results on flow harmonics, determined from the cumulants of up to eight-particle correlations, will be shown over a wide transverse momentum, 0.5<pT<20 GeV, pseudorapidity (|eta|<2.5) and centrality ranges. The applied cumulant approach provides a unique handle on non-flow effects and allows for the evaluation of the genuine flow fluctuations. Derived estimates of the non-flow correlations and the magnitude of flow fluctuations will be discussed. Centrality and pseudorapidity dependence of the elliptic flow integrated down to very low pT will also be shown and compared to the LHC results as well as to low energy data. A hypothesis of the energy scaling will be examined taking advantage of the large pseudorapidity coverage of the ATLAS experiment.Speaker: Tomasz Bold (AGH Univ. of Science amp; Technology, Krakow)
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Two particle correlation measurements with respect to higher harmonic event planes at PHENIX 20mTwo particle correlations provide key information on the interactions between hard-scattered partons and the hot dense medium created by ultra-relativistic heavy ion collisions. An important aspect of extracting jet functions from correlation measurements in heavy ion collisions is to estimate the underlying event background level and its modulation by vn. This is essential for the goal of discerning possible medium response to hard-scattered partons. At both RHIC and the LHC, higher harmonic flow(vn) has recently been measured over a large rapidity range. Harmonics beyond v2 provide sensitivity to fluctuations of the initial collision geometry. After subtracting vn component of the background, we are able to construct correlations in which the trigger particle is selected with respect to not only the second, but also higher, harmonic event planes. These provide detailed knowledge of the path length dependence of parton energy loss and its sensitivity to each harmonic event plane. This talk will present the current results of azimuthal hadron correlations both with and without trigger selection relative to higher harmonic event planes in Au+Au 200 GeV collisions.Speaker: Takahito for the PHENIX Collaboration Todoroki (University of Tsukuba, RIKEN Nishina Center)
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Hydrodynamic fluctuations in expanding medium 20mWe describe intrinsic hydrodynamic fluctuations of the expanding boost-invariant (Bjorken) solution. We find that these fluctuations are correlated over a wide rapidity range due to the propagation of the sound modes, whose dispersion is nontrivial because of the expansion. Since the magnitudes of these correlations are proportional to viscosities, their measurement can, in principle, be used to obtain information about the transport coefficients as well as thermodynamic properties of the medium.Speaker: Prof. Misha Stephanov (UIC)
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Mapping the hydrodynamic response to the initial geometry in heavy-ion collisions 20mWe investigate how the initial geometry of a heavy-ion collision is transformed into final flow observables by solving event-by-event ideal hydrodynamics with realistic fluctuating initial conditions. We study quantitatively to what extent anisotropic flow ($v_n$) is determined by the initial eccentricity $\varepsilon_n$ for a set of realistic simulations, and we discuss which definition of $\varepsilon_n$ gives the best estimator of $v_n$. We find that the common practice of using an $r^2$ weight in the definition of $\varepsilon_n$ in general results in a poorer predictor of $v_n$ than when using $r^n$ weight, for $n > 2$. We similarly study the importance of additional properties of the initial state. For example, we show that in order to correctly predict $v_4$ and $v_5$ for non-central collisions, one must take into account nonlinear terms proportional to $\varepsilon_2^2$ and $\varepsilon_2\varepsilon_3$, respectively. We find that it makes no difference whether one calculates the eccentricities over a range of rapidity, or in a single slice at $z=0$, nor is it important whether one uses an energy or entropy density weight. This knowledge will be important for making a more direct link between experimental observables and hydrodynamic initial conditions, the latter being poorly constrained at present.Speaker: Fernando Gardim (USP)
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Parallel 6E: Initial State and p-A (Chair E. Wang) Empire
Empire
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Thermalization and Possible Bose-Einstein Condensation in Over-populated Glasma 20mWe report on a recently proposed scenario for thermalization of hot QCD matter after the "Little Bang" in heavy ion collisions. A distinctive feature of the pre-equilibrium system (the Glasma) is the high over-population of phase space for gluons, which we argue plays a central role for the thermalization of the Quark-Gluon Plasma. In particular, the over-population (1) coherently amplifies scattering by $1/\alpha_s$ and makes the system behave as a strongly interacting fluid despite being out of equilibrium at weak coupling, (2) may lead to the dynamical, albeit transient formation of a Bose-Einstein condensate over the course of thermalization. A further distinctive feature of our scenario is that the initially single scale ($Q_s$) of Glasma develops into a hierarchy of scales, with the IR scale and the UV separated by coupling $\alpha_s$, precisely as in equilibrium thermal field theory. We demonstrate these features by solving the Boltzmann equation in the small angle approximation and in the regime where the occupation numbers are large. Finally, we address possible phenomenological consequences of our scenario.Speaker: Jinfeng Liao (Indiana University & RIKEN BNL Research Center)
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A New Mechanism for Generating a Single Transverse Spin Asymmetry 20mWe propose a new mechanism for generating a single transverse spin asymmetry (STSA) in polarized proton-proton and proton-nucleus collisions in the high-energy scattering approximation. In this framework the STSA originates from the q -> q G splitting in the projectile (proton) light-cone wave function followed by a perturbative (C-odd) odderon interaction, together with a C-even interaction, between the projectile and the target. We show that the obtained expression for the STSA of the produced quarks is in qualitative agreement with experiment: STSA decreases with decreasing projectile x_F and is a non-monotonic function of the transverse momentum k_T, peaking near the saturation scale Q_s in our framework. Our mechanism predicts that the quark STSA in proton--nucleus collisions should be much smaller than in proton--proton collisions. We also observe that in our formalism the STSA for prompt photons is zero.Speaker: Mr Matthew Sievert (The Ohio State University)
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Drell-Yan Lepton-Pair-Jet Correlation in pA collisions 20mWe have recently performed a numerical study of the forward correlations between the lepton-pair and associated hadrons in Drell-Yan process in pA collisions. Using the present knowledge of the dipole gluon distribution from the modified Golec-Biernat-Wusthoff model and from the solution of the Balitsky-Kovchegov evolution equation, we are able to compute and predict the forward correlations between the lepton-pair and associated hadron in Drell-Yan process at RHIC and LHC. Similar to the forward dihadron correlation in dAu collisions measured at RHIC, the Drell-Yan type correlation also implies a strong suppression of the away side hadron at forward rapidity due to the strong interaction between the forward quark from the projectile proton and the gluon density from the target nucleus. Another feature of this process is that the correlation contains a double-peak structure in the away side, which makes it a unique observable.Speaker: David Zaslavsky (Penn State University)
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The NLO inclusive forward hadron production in pA collisions 20mRecently, by performing the complete next-to-leading order calculation, we have demonstrated the one-loop factorization for inclusive hadron productions in pA collisions in the saturation formalism. The differential cross section is written into a factorization form in the coordinate space at the next-to-leading order, while the naive form of the convolution in the transverse momentum space does not hold. The rapidity divergence with small-x dipole gluon distribution of the nucleus is factorized into the energy evolution of the dipole gluon distribution function, which is known as the Balitsky-Kovchegov equation. Furthermore, the collinear divergences associated with the incoming parton distribution of the nucleon and the outgoing fragmentation function of the final state hadron are factorized into the splittings of the associated parton distribution and fragmentation functions, which allows us to reproduce the well-known DGLAP equation. The hard coefficient function, which is finite and free of divergence of any kind, is evaluated at one-loop order. This result is important, not only for the phenomenological applications to the inclusive hadron production in p-A collisions at RHIC and future LHC experiment, but also for theoretically promoting the rigorous developments towards a complete QCD factorization in small-x physics.Speaker: Dr Bowen Xiao
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Dijet Correlations in the Forward pA (eA) Collisions to Map the Phase Structure of Cold Nuclei Matter at Small-x 20mAs the foundation of high energy hadronic physics, QCD factorization enables us to separate the short distance perturbative physics from the long distance non-perturbative effects. Its prediction power relies on the universality of the parton distributions among different processes. In our recent publication [1], we established an effective factorization in hard processes in nuclei scattered by a dilute probe. This factorization enables us to identify the key observables to probe the so-called unintegrated gluon distributions, the central objects in the saturation framework. This has been a long-standing issue in small-x physics. From our studies, we found that the dijet-correlations in deep inelastic scattering of electron-nucleus collisions directly measure the Weizacker-Williams gluon distribution function, whereas the photon-jet correlation in nucleon-nucleus (pA) collisions probes the dipole gluon distribution. The dijet (di-hadron) correlations in pA collisions can probe both gluon distributions. Current experiments in deuteron-gold (dAu) collisions at RHIC, and future pA collisions at LHC, and the planed electron-ion collider (EIC) experiments, will provide great opportunities to study two-particle collisions and the associated strong interaction dynamics of the gluon distributions in cold nucleus at small-x. Recently, both STAR and PHENIX collaborations have reported the measurements of two-hadron correlations in the forward direction of dAu collisions at RHIC [2], where the strong de-correlation of the away-side hadron have been considered as the best evidence for saturation physics. The numeric calculations based on our factorization formalism provides a quantitative and thorough description of the experimental data in the saturation formalism [3], including the large broadening of the angular distribution and suppression of the peak for the away-side hadron. The disappearing of the away-side peak in central collisions indicates that the saturation scale is the same order as the hard jet transverse momentum, which is a clear signal of the onset of the saturation. From the kinematics, we conclude that the saturation scale reaches 2GeV at x~6x10-4 in the center of the gold nucleus with jet transverse momentum kt~3GeV at rapidity 3.2. Future measurements at RHIC and LHC and the planed EIC will provide more information and help to map out the complete phase structure of the cold nuclei matter at small-x. [1] F. Dominguez, B. Xiao and F. Yuan, kt-factorization for Hard Processes in Nuclei, Phys. Rev. Lett. 106, 022301 (2011); F. Dominguez, C. Marquet, B.W. Xiao and F. Yuan, Universality of Unintegrated Gluon Distributions at small x, Phys. Rev. D83, 105005 (2011). [2] E. Braidot, for the STAR Collaboration, Two Particle Correlations at Forward Rapidity in STAR, Nucl. Phys. A 854, 168 (2011); A. Adare, et al., [PHENIX Collaboration], Suppression of back-to-back hadron pairs at forward rapidity in d+Au Collisions at \sqrt{s}_{NN}}=200GeV, Phys. Rev. Lett. 107, 172301 (2011). [3] A. Stasto, B. Xiao, F. Yuan, Back-to-Back Correlations of Di-hadrons in dAu Collisions at RHIC, e-Print: arXiv:1109.1817 [hep-ph].Speaker: Feng Yuan (LBNL)
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Influence of initial state fluctuations on the production of thermal photons 20mThermal emission of photons from relativistic heavy ion collisions is believed to have a very strong temperature dependence and the high p_T thermal photons are expected to provide a glimpse of the early part of the expansion history when the system is still in the plasma phase. Photons having p_T > 1 GeV/c are thus specially suitable for probing fluctuations in the initial QCD matter density distributions. We present the p_T spectra, ratio of central to-peripheral yield and elliptic flow of thermal photons from an event-by-event ideal hydrodynamic calculation with fluctuating initial conditions (IC). We show that fluctuations in the IC enhance the production of thermal photons significantly in the range 2 < p_T < 4 GeV/c compared to a smooth initial-state-averaged profile for Au+Au (Pb+Pb) collisions at RHIC (LHC) [1,2]. The relative effect of fluctuations in the IC is found to be stronger for peripheral collisions and for lower beam energies. Thermal photon p_T spectra are studied for different values of initial formation time \tau_0 as well as for centrality dependent \tau_0 values. We show that a suitably normalized ratio of central-to-peripheral yield as a function of collision centrality and p_T can be a useful measure of the fluctuation size scale [2]. PHENIX data for direct photon elliptic flow at RHIC is found to be significantly larger than the v_2 results obtained using ideal hydrodynamics with smooth IC in the region 1 < p_T < 6 GeV/c. We show that fluctuations in the IC increase the elliptic flow for p_T > 2 GeV/c for mid-central collisions compared to the results from a smooth initial-state-averaged profile [3]. We also show that these results depend strongly on the value of the fluctuation size scale as well as on the initial and final conditions of the hydrodynamic calculation [3]. [1] R. Chatterjee, H. Holopainen, T. Renk, and K. J. Eskola, Phys. Rev. C 83, 054908 (2011); R. Chatterjee, H. Holopainen, T. Renk, and K. J. Eskola, J. Phys. G 38, 124136 (2011). [2] R. Chatterjee, H. Holopainen, T. Renk, and K. J. Eskola, arXiv:1204.2249 [nucl-th]. [3] R. Chatterjee, H. Holopainen, T. Renk, and K. J. Eskola [in preparation].Speaker: Dr Rupa Chatterjee (University of Jyväskylä)
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Coffee Break 30m Bird Cage & Regency Gallery
Bird Cage & Regency Gallery
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Parallel 7A: Heavy Flavor & Quarkonia (Chair F. Antinori) Ambassador
Ambassador
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Measurement of the nuclear modification factor and v2 of electrons from heavy flavour decays in Pb-Pb collisions at 2.76 TeV with ALICE 20mIn heavy-ion collisions, charm and beauty (heavy flavour) quarks are produced primarily in the initial, hard partonic interactions. They successively interact with the hot and dense Quark-Gluon Plasma (QGP) expected to be formed in such collisions. Therefore, measurements of heavy flavour production provide relevant information on the properties of the QGP. This talk presents measurements by the ALICE Collaboration of electrons from heavy flavour decays at central rapidity in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. Electrons are identified using several detectors of the ALICE central barrel. Electrons from beauty decays are separated based on their displacement from the interaction vertex. The nuclear modification factor of inclusive electrons from heavy flavour decays and of electrons from beauty decays, as a function of transverse momentum and collision centrality, will be presented.Speaker: Shingo Sakai (Lawrence Berkeley National Lab. (US))
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Measurements of Non-photonic Electrons Production and Elliptic Flow in 39, 62.4 and 200 GeV Au+Au Collisions from STAR at RHIC 20mHeavy quarks are produced early in the heavy-ion collisions and are expected to interact with the created strongly interacting partonic medium differently from light quarks. Therefore, they can shed new light on understanding the medium's properties. Simultaneous measurements of spectra and elliptic flow of electrons from semileptonic decays of heavy flavor hadrons at different collision energies and centralities can provide experimental insight to distinguish different energy loss theoretical models and to characterize the degree of thermalization of heavy quarks at different energies. We will present STAR measurements of non-photonic electrons at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}} = 39$, $62.4$ and $200$ GeV. The data were taken during 2010 run with detector configurations for minimum photonic conversion background. Both the invariant yields and elliptic flow measurements will be reported as a function of $p_T$, centrality and collision energy. We will also report non-photonic electrons nuclear modification factor, $R_{AA}$, at $\sqrt{s_{NN}} = 200$GeV.Speaker: Mustafa Mustafa (Purdue University)
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Measurement of muon tagged b-jet production in Pb+Pb collisions at 2.76 TeV with the ATLAS detector at the LHC 20mBottom quark is a very important probe to study the hot, dense medium produced in the heavy ion collisions. Bottom quark is produced at the relatively early stage of the nucleus-nucleus collisions and may have a small gluon radiation due to a suppression of small angle gluon radiation `dead cone effect’. Because the heavy mass of b-hadrons, muons from semi-leptonic b-hadron decays tend to have larger angle with respect to the jet axis. This information can be used to tag b-jets. Specifically, the transverse momentum of the muon with respect to the b-jet axis, pT^{rel}, is used to differentiate b-jets from the background charm and light quark jets. In this talk, we present the b-jet suppression R_CP, which is defined as the ratio of the average N_coll scaled yield in central collisions to that in peripheral collisions (60-80%), as a function of the muon momentum, jet momentum and the number of participants average N_part in Pb+Pb collisions at 2.76 TeV. The result is also compared with the inclusive heavy flavor suppression, which was obtained by studying single muons decayed semi-leptonically from the from the b- and c-quark containing hadrons.Speaker: Dennis Perepelitsa (Columbia University)
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Elliptic flow of J/psi at forward rapidity in Pb-Pb Collisions at 2.76 TeV with the ALICE experiment 20mCharmonium production in heavy ion collisions has been studied at different energies and with different collision systems over the last few decades, ever since the J/psi suppression induced by color screening of its constituent quarks was proposed as a signature of the formation of a quark gluon plasma (QGP) in heavy-ion collisions. The recent measurement of the J/psi production in Pb-Pb collisions at forward rapidity performed by ALICE at the LHC clearly showed less suppression with respect to SPS and RHIC results. The J/psi elliptic flow v2 provides an important tool to test the degree of J/psi thermalisation in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. It may also help in understanding the J/psi (re)generation mechanism in the QGP, which is expected to play a more important role at LHC energies. We present the elliptic flow of J/psi measured in the dimuon channel at forward rapidity ( 2.5 < y < 4.0 ) with the ALICE muon spectrometer, down to zero transverse momentum. The centrality dependence of the pt-integrated elliptic flow will be discussed. In addition, the pt and rapidity dependence in several centrality classes will be presented, as well as the systematical studies based on using various methods for measuring the elliptic flow. Finally, results will be compared with existing measurements at RHIC and theoretical calculations.Speaker: Hongyan Yang (CEA - Centre d'Etudes de Saclay (FR))
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Nuclear Modification Factor and Elliptic Flow of Muons from Open Heavy Flavour Decays at Forward Rapidity in Pb-Pb Collisions at 2.76 TeV with ALICE 20mHeavy quark production is one of the probes for investigating the properties of the high-density medium formed in heavy-ion collisions at high energy. The suppression of heavy flavour production, at high momentum, quantified via the nuclear modication factor is used to study the in-medium energy loss mechanism of heavy quarks. The measurement of the collective flow of heavy flavours provides insights on the possible thermalization of heavy quarks in the medium. Heavy flavour production at forward rapidity is measured in ALICE using semi-muonic decays. We present results on the pt-differential nuclear modification factor RAA and elliptic flow of muons from heavy flavour decays in the rapidity range 2.5 < y < 4 in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV.Speaker: Xiaoming Zhang (Univ. Blaise Pascal Clermont-Fe. II (FR))
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Parallel 7B: Exploring the QCD Phase Diagram (Chair H. Huang) Regency 2/3
Regency 2/3
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The RHIC Beam Energy Scan Program: Results from the PHENIX Experiment 20mMany recent lattice QCD calculations predict that there may be a first order phase transition from hadronic matter to a Quark-Gluon Plasma that ends in a critical point, with a continuous phase transition on the other side of the critical point. The Relativistic Heavy Ion Collider (RHIC) has conducted a program to probe different regions of the QCD phase diagram in the vicinity of the possible critical point with a beam energy scan. During 2010 and 2011, RHIC provided Au+Au collisions to PHENIX at $\sqrt(s_NN)=$ 200 GeV, 62.4 GeV, 39 GeV, 27 GeV, 19.6 GeV, and 7.7 GeV. Analysis of the data concentrates on two strategies: looking for signs of the onset of deconfinement by comparing to results at the top RHIC energy, and searching for direct signatures of a critical point. Results presented will include the following: charged particle multiplicity at mid-rapidity, transverse energy production at mid-rapidity, energy loss via the $R_{AA}$ and $R_{CP}$ observables from a variety of identified particles including neutral pions and the $J/\psi$, collective flow measurements ($v_{2}$, $v_{3}$, $v_{4}$) from various particles including neutral pions, charged hadrons, and identified particles in order to examine the validity of the number of constituent quark scaling at lower energies, higher moments of the net charge distribution, and fluctuations of the charged particle multiplicity.Speaker: Jeffery Mitchell (Brookhaven National Laboratory)
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Beam energy and centrality dependence of the statistical moments of the net-charge multiplicity distribution in Au+Au collisions at STAR 20mIn part to search for a possible critical point (CP) in the phase diagram of hot nuclear matter, a beam energy scan was performed at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory. The STAR experiment collected significant Au+Au data sets at beam energies, $\sqrt{\rm s_{\rm NN}}$, of 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV. Lattice and phenomenological calculations suggest that the presence of a CP might result in divergences of the thermodynamic susceptibilities and correlation lengths [1,2]. The statistical moments of the multiplicity distributions of particles reflecting conserved quantities, {\it e.g.} net-charge and net-strangeness, are expected to depend sensitively on these correlation lengths, making them attractive tools for the search of a possible critical point. In this talk, the centrality and beam energy dependence of the statistical moments of the net-charge multiplicity distributions will be presented. The observables studied include the lowest four statistical moments (mean, variance, skewness, kurtosis), products of these moments, and the intensive normalized cumulants [2]. The measured moments of the net-Kaon and total-pion multiplicity distributions will also be presented. These will be compared to the predictions from approaches lacking critical behavior, such as the Hadron Resonance Gas model [3] and Poisson statistics. References [1] M. Cheng {\it et al.}, Phys. Rev. D 79, 074505 (2009). [2] C. Athanasiou {\it et al.}, Phys. Rev. D 82, 074008 (2010), M. Stephanov, Phys. Rev. Lett. 107, 052301 (2011). [3] F. Karsch and K. Redlich, Phys. Lett. B 695, 136 (2011).Speaker: Daniel McDonald (R)
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Baryon number conservation and cumulants of net proton distribution 20mWe discuss the effects of the global baryon and electric charge conservation on the cumulants of net baryon and net proton fluctuations [1], which are considered to be sensitive probes of the QCD critical point. We show that the cumulants are substantially suppressed if the conservation laws are taken into account. We propose a new observable that is not influenced by the global baryon conservation but is highly sensitive to the critical end point or the crossover. [1] A. Bzdak, V. Koch, V. Skokov, arXiv:1203.4529 [hep-ph]Speaker: Adam Bzdak (Brookhaven National Laboratory)
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Search for the QCD Critical Point by Higher Moments of Net-proton Multiplicity Distributions at STAR 20mOne of the main goals of the RHIC Beam Energy Scan (BES) Program is to search for the QCD Critical Point and the phase boundary in the QCD phase diagram. Higher moments of event-by-event net-proton multiplicity distributions have high sensitivity to the correlation length[1], and they are directly connected to the susceptibilities in the Lattice Gauge Theory (LGT) calculations and the Hadron Resonance Gas (HRG) model. Therefore, they are ideal tools to search for the QCD critical point[4] In this talk, we will present various moments (variance [σ^2], skewness[S] and kurtosis [κ], moment products (κσ^2, Sσ) and intensive normalized cumulants (ω3 and ω4) of net-proton and total-proton multiplicity distributions measured by the STAR detector at RHIC. The moment products (κσ^2, Sσ) and intensive normalized cumulants are related to the volume independent susceptibility ratios. The data presented in this talk will include the measurements of centrality dependence for the net-protons and total-protons from Au+Au collisions at √sNN = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV. These results have been compared with a Poisson baseline. It is observed that the moment products (κσ^2, Sσ) and intensive normalized cumulants of net-proton distributions in the 0-5% most central Au+Au collisions show significant deviations from the Poisson expectations around √sNN = 19.6 GeV. Those results will be also compared with UrQMD model calculations. [1] M. A. Stephanov, Phys. Rev. Lett. 102, 032301 (2009); Phys. Rev. Lett. 107, 052301 (2011); C. Athanasiou, et al., Phys. Rev. D 82, 074008 (2010). [2] M. Cheng, et al., Phys. Rev. D 79, 074505 (2009). R. V. Gavai and S. Gupta, Phys. Lett. B 696, 459 (2011). S. Gupta, X. Luo, B. Mohanty, H. G. Ritter, N. Xu, Science 332, 1525 (2011). A. Bazavov, et al., (HotQCD Collaboration), arXiv:1203.0784 [3] F. Karsch and K. Redlich, Phys. Lett. B 695, 136 (2011). [4] M. M. Aggarwal, et al., (STAR Collaboration), Phys. Rev. Lett. 105, 22302 (2010).Speaker: Dr Xiaofeng Luo (Central China Normal University)
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Report from NA49 and NA61/SHINE at the CERN SPS 20mRecent results from the study of nucleus-nucleus as well as proton-proton collisions at the CERN SPS energies from experiment NA49 and its successor NA61/SHINE will be summarized. New results from a novel fluctuation analysis and from the search for the critical point of strongly interacting matter will be discussed. First measurements from NA61 of the energy dependence of identified hadron production in inelastic p+p interactions will be presented and compared with the corresponding results in central Pb+Pb collisions from NA49. In particular, inclusive spectra and mean multiplicities as well as particle fluctuations and correlations will be shown. Finally, the status of the NA49 evidence for the onset of deconfinement will be reviewed in view of new results from NA61, STAR and ALICE. An outlook on the NA61/SHINE program will be given.Speaker: Anar Rustamov (Johann-Wolfgang-Goethe Univ. (DE))
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Parallel 7C: New Experimental Developments (Chair T. Peitzmann) Palladian
Palladian
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NICA @ JINR 20mScientific program of NICA (Nuclotron-based Ion Collider fAcility) is now under realization phase at JINR (Dubna). The main goal of the program is an experimental study of hot and dense strongly interacting matter in heavy ion collisions at nucleon-nucleon centre-of-mass energies of 4-11 GeV and at average luminosity of 10E27 cm-2s-1 for Au (79+) in the collider mode. In parallel, fixed target experiments at the upgraded JINR superconducting synchrotron Nuclotron are carried out with the extracted beams of various nuclei species up to gold with the momenta up to 13 GeV/c for protons. The program also foresees a study of spin physics with extracted and colliding beams of polarized deuterons and protons at the centre-of-mass energies up to 26 GeV for proton collisions. The proposed program allows to search for possible signs of the mixed phase and critical endpoint, and to shed more light on the problem of nucleon spin structure. General design and construction status of the complex is presented.Speaker: Richard Lednicky (Joint Institute for Nuclear Research, Dubna, Russia)
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Exploring Gluonic Matter with Electron-Ion Collisions 20mHeavy nuclei probed in deep inelastic scattering and diffraction with leptonic probes in the high-energy (small-x) regime open a new precision window into answering fundamental questions in QCD. The proposed electron-ion collider at BNL (eRHIC) will be a new high-energy and high-luminosity electron-ion/proton machine. The design offers unprecedented access to study the nature of QCD matter and strong color fields. In particular, the new collider will allow us to explore the properties of gluon saturation, which is one of the fundamental outstanding problems in QCD. The compelling physics case for the electron-Ion collider is presented with a focus on studying saturated gluonic matter in the context of the initial condition of the high-energy heavy-ion collisions at RHIC and LHC. In this talk, we will discuss how selected key measurements - dihadron correlation and exclusive diffractive vector meson production can be used to probe and characterize the gluonic matter produced at small-x in eA collisions.Speaker: J.H. Lee (Brookhaven National Laboratory)
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The Large Hadron-electron Collider at CERN 20mThe project of a new experimental facility at CERN, the Large Hadron-electron Collider, which will collide electrons against the LHC beams at center-of-mass energies around 1 TeV per nucleon, will be presented. After a brief introduction and showing the proposals for accelerator and detector, the physics opportunities for QCD studies will be discussed. Specifically, I will focus on the possibilities with heavy ions, for improving our knowledge on the parton densities, small-x dynamics and particle production mechanism through inclusive, diffractive and exclusive measurements, plus final state studies.Speaker: Anna Stasto (Pennsylvania State University (US))
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Prospective for A Fixed-Target ExpeRiment at the LHC: AFTER@LHC 20mWe outline the physics opportunities~\cite{Brodsky:2012vg} which are offered by a next generation and multi-purpose fixed-target experiment exploiting the LHC beams extracted by a bent crystal. This mature extraction technique offers an ideal way to obtain a clean and very collimated high-energy beam, without altering the performance of the LHC~\cite{Uggerhoj:2005xz,Scandale:2011zz,LUA9}. The multi-TeV LHC beams grant the most energetic fixed-target experiment ever performed, to study \pp, \pd\ and \pA\ collisions at \mbox{$\sqrt{s_{NN}} \simeq 115\,\mathrm{GeV}$} and \PbA\ collisions at \mbox{$\sqrt{s_{NN}} \simeq 72\,\mathrm{GeV}$}. AFTER -- for A Fixed-Target ExperRiment -- gives access to new domains of particle and nuclear physics complementing that of collider experiments, in particular RHIC and the projects of electron-ion colliders. The typical instantaneous luminosity achievable with AFTER in \pp\ and \pA\ mode~\cite{Brodsky:2012vg} surpasses that of RHIC by more than 3~orders of magnitude and is comparable to that of the LHC collider mode. This provides a quarkonium and heavy-flavour observatory in \pp\ and \pA\ collisions where, by instrumenting the target-rapidity region, gluon and heavy-quark distributions of the proton, the neutron and the nuclei can be accessed at large $x$ and even at $x$ larger than unity in the nuclear case. The nuclear target-species versatility provides a unique opportunity to study cold nuclear matter versus the features of the hot and dense matter formed in heavy-ion collisions, including the formation of the quark-gluon plasma. During the one-month lead runs, \PbA\ collisions can be studied at a luminosity comparable to that of RHIC and the LHC over the full range of target-rapidity domain. Modern detection technology should allow for the study of quarkonium excited states, in particular the $\chi_c$ and $\chi_b$ resonances, even in the challenging high-multiplicity environment of \pA\ and \PbA\ collisions, magnified by the boost of the fixed-target mode. Precise data from \pp, \pA\ and \PbA\ should help to greatly improve our understanding of heavy-quark and quarkonium production, to clear the way to use them for gluon and heavy-quark PDF extraction in free and bound nucleons, to unravel cold from hot nuclear effects and to restore the status of heavy quarkonia as a golden test of lattice QCD in terms of dissociation temperature predictions at a \sqrtsNN\ where the recombination process is expected to have a small impact. The fixed-target mode also has the advantage to allow for spin measurements with polarized targets. We will discuss a tentative design for AFTER, and report the projected detector performances from the first preliminary simulations. \begin{thebibliography}{4} \bibitem{Brodsky:2012vg} S.~J.~Brodsky, F.~Fleuret, C.~Hadjidakis and J.~P.~Lansberg, arXiv:1202.6585 [hep-ph]. %%CITATION = ARXIV:1202.6585;%% \bibitem{Uggerhoj:2005xz} E.~Uggerh\o j, U.~I.~Uggerh\o j, Nucl.\ Instrum.\ Meth.\ B {\bf 234} (2005) 31. %%CITATION = NUIMA,B234,31;% \bibitem{Scandale:2011zz} W.~Scandale, {\it et al.}, Phys.\ Lett.\ {\bf B703 } (2011) 547-551. \bibitem{LUA9} W.~Scandale, {\it et al.} [LUA9], CERN-LHCC-2011-007, 2011.Speaker: Andry Malala Rakotozafindrabe (CEA - Centre d'Etudes de Saclay (FR))
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Parallel 7D: Correlations & Fluctuations (Chair B. Wosiek) Diplomat
Diplomat
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Forward/backward, reaction-plane dependent J/psi production and hadron v_n in Cu+Au collisions in PHENIX 20mThe flexibility of RHIC to collide different nuclei provides experiments with a rich resource to systematically test models and scaling behaviors and compare the results to those from Au+Au collisions. For an initial evaluation of the Cu+Au collision system, PHENIX has earmarked several measurements for fast analysis, in particular, forward/backward and central-rapidity J/psi production. These collisions promise an array of unique geometrical configurations including odd harmonics and events where the Cu nucleus is completely embedded within the Au. Such geometries present an opportunity to probe the "core" and "corona" regions of the collision (which are strongly asymmetric in Cu+Au) by measuring the reaction plane dependence of particle production. J/psi production may be more sensitive to the least dense part of the collision at the surface - the corona - thus providing a handle of the relative size of the Cu- versus Au-side corona. An important component of this analysis is the understanding of the light-hadron vn(n=1,2,3,4) and the correlation between the vn event planes in these collisions, which will reveal the underlying hydrodynamical properties of the system. In particular, the odd harmonics from the Cu+Au system offer sensitivity to v3 generated from the collision geometry as opposed to fluctuations in a symmetric system. The analysis status of the recently taken U+U collision data, which offers some of the same advantages as Cu+Au, as well as a wider range of energy densities, will also be presented.Speaker: Dr Richard Hollis (University of California, Riverside)
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Measurement of event plane correlations in Pb-Pb collisions with the ATLAS detector 20mRecently harmonic flow coefficients v_1-v_6 have been measured in heavy-ion collisions at LHC. The magnitude of these coefficients and their centrality dependence suggest that they are associated with the various shape components in the initial geometry, arising from fluctuations of the participating nucleons in the overlap region. The orientation of these harmonic flow (event plane or Psi_n) are generally correlated due to the correlations between the original shape components in the initial geometry; the correlations between event plane can also be generated dynamically during the hydrodynamic evolution of the medium. We present first measurements of various event plane correlations involving Psi_2 to Psi_6 in Pb-Pb collisions at the LHC. The large detector acceptance of ATLAS, i.e. calorimeter covering -5<eta<5 and tracking detector covering -2.5<eta<2.5, allows for a precise measurement of these correlations. The procedure for obtaining these correlations and the detailed comparison of the results obtained from sub-events in different eta ranges are discussed.Speaker: Soumya Mohapatra (State University of New York (US))
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Anisotropic flow measured from multi-particle azimuthal correlations for Pb-Pb collisions at 2.76 TeV by ALICE at the LHC 20mThe properties of the produced matter in a heavy-ion collision can be experimentally studied by measuring the azimuthal anisotropy in the momentum distribution of the produced particles. Quantified by the anisotropic flow coefficients, v_n, and corresponding symmetry planes, psi_n, such anisotropy is expected to reflect the shape of the initial energy density of the collision. We report on the measurement of various flow harmonics, v_n, with multi-particle cumulants, and present the results from a study of the inter-correlation among different order symmetry planes psi_n via multi-particle mixed harmonic correlations. This provides comprehensive experimental information on the fluctuating event-by-event shape of the initial conditions, which is currently among the main sources of large theoretical uncertainties in describing the evolution of the system created in heavy-ion collisions.Speaker: Ante Bilandzic (Niels Bohr Institute (DK))
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Studies of higher-order flow harmonics and factorization of dihadron correlations in PbPb collisions at 2.76 TeV with CMS 20mThe higher-order flow anisotropies of charged particles have been systematically studied by the CMS collaboration for PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV. The data were collected with the CMS detector at the LHC in 2010 and 2011. Fourier components of the anisotropic azimuthal distribution, ranging from the third to the sixth component, are obtained using four different analysis techniques: event plane, two- and four-particle correlations, and Lee-Yang Zeros. The results are reported as a function of the particle transverse momentum (pT) for pT = 0.5 - 20 GeV/c and collision centrality. The long-range azimuthal dihadron correlations are extensively studied with a Fourier-decomposition analysis. Using a data driven method, the extracted Fourier coefficients (up to the fifth order) are found to factorize into a product of single-particle azimuthal anisotropies up to pT~3-3.5 GeV/c for at least one particle from each pair, except for the second-order harmonics in the most central PbPb events. Based on the factorization studies, the implications of flow and non-flow effects in the long-range correlations are discussed. Comparison of higher-order harmonics derived from different techniques provides important insight on the initial-state eccentricity fluctuations and helps further constrain the transport properties of the medium.Speaker: Shengquan Tuo (Vanderbilt University (US))
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Pseudorapidity dependence of the anisotropic flow with ALICE at the LHC 20mThe anisotropic flow at forward rapidity provides information on the longitudinal expansion of the system produced in a heavy-ion collision. We report on the pseudo-rapidity dependence of the charged particle anisotropic flow in Pb-Pb collisions at 2.76 TeV. The measurement is done over a wide range of pseudo-rapidity, |\eta|<5.1 using the forward detectors of ALICE at the LHC. Results are obtained from two- and multi-particle correlation techniques with the latter being less sensitive to non-flow effects. The longitudinal scaling of the anisotropic flow at the LHC and the comparison with RHIC measurements and hydrodynamical model calculations at forward rapidity will be discussed.Speaker: Alexander Hansen (University of Copenhagen (DK))
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Parallel 7E: New Theoretical Developments (Chair P. Levai) Empire
Empire
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Evolution of singularities in unequal time two-point correlator in formation of QGP 20mOne of the most difficult problems still to be understood is the mechanism of fast thermalization in heavy ion collisions. The problem involves dynamics in strong coupling regime and physics far from equilibrium, therefore is hardly tractable by usual method. The gauge/gravity duality naturally maps the formation of quark gluon plasma to another fundamental problem in black hole physics: information loss in a gravitational collapse process. The present work summarizes our recent results on the study of a particular probe: unequal time two-point correlator for gauge theory in the evolution toward thermal equilibrium. In [1], we found that near equilibrium the spectral functions showed a universal pattern as field equilibrates in a quasi-static approximation. We have then systematically extended the previous work to the far from equilibrium region by using the coordinate representation. In the past two years we have developed a divergence matching method in computing the singularities of the unequal time two-point correlator in a time-dependent background. We found the singularities have a nice interpretation with a geometric optics picture [2,3]. Applying this method to the gravitational collapse model, we found the singularities of the unequal time correlator shifted from the real time to the complex time in the formation of QGP [4]. This signature sheds more light on the mechanism of the thermalization and may have interesting implications to heavy ion phenomenology and experiments. [1] S.~Lin and E.~Shuryak, %``Toward the AdS/CFT Gravity Dual for High Energy Collisions. 3. Gravitationally Collapsing Shell and Quasiequilibrium,'' Phys.\ Rev.\ D {\bf 78}, 125018 (2008) [arXiv:0808.0910 [hep-th]]. [2] J.~Erdmenger, S.~Lin and T.~H.~Ngo, %``A Moving mirror in AdS space as a toy model for holographic thermalization,'' JHEP {\bf 1104}, 035 (2011) [arXiv:1101.5505 [hep-th]]. [3] J.~Erdmenger, C.~Hoyos and S.~Lin, %``Time Singularities of Correlators from Dirichlet Conditions in AdS/CFT,'' JHEP {\bf 1203}, 085 (2012) [arXiv:1112.1963 [hep-th]]. [4] J.~Erdmenger and S.~Lin, to appearSpeaker: Shu Lin
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Derivation of the medium-induced splitting kernels from Soft Collinear Effective Theory with Glauber gluons 20mWe derive the splitting kernels for partons produced in large Q^2 scattering processes that subsequently traverse a region of strongly-interacting matter using a recently-developed effective theory Soft Collinear Effective Theory with Glauber Gluons (SCETG). We include all corrections beyond the small-x approximation, consistent with the power counting of SCETG. We demonstrate how medium recoil, geometry, expansion scenarios, and phase space cuts can be implemented numerically for phenomenological applications and quantify the effect of these uncertainties. We also prove the factorization of the medium-induced splitting from the hard process that creates the jet. We show that in the soft gluon approximation our result reduces to the parton energy loss obtained in the framework of the reaction operator approach. This limit is illustrated with an application to inclusive hadron suppression and comparison to the new ALICE and CMS results at the LHC. We discuss ongoing work on obtaining next-to-leading order splitting kernels in the medium and possible applications to heavy ion event generators.Speaker: grigory ovanesyan (LANL)
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Dissipative effects in multi-component systems 20mWe demonstrate that the shear viscosity of a two-component mixture of point-like partices has a non-trivial time dependence, which is induced by the intrinsic coupling between the two particle species. The shear viscosity coefficient of a mixture calculated using the Green-Kubo relation does not have this time dependence and hence is not sufficient to describe dissipatie hydrodynamic behavior of a mixture. In particular this means, that the shear viscosity to entropy density values of a QGP or a hadron gas obtained from comparisons of elliptic flow $v_2$ calculated in standard one-component hydrodynamic with measurements done at RHIC and LHC must also contain a time-dependence characterisitc for the mixture, which so far has never been taken into account. The results we present here are obtained using the kinetic transport model BAMPS as well as dissipative hydrodynamic calculations in 2+1 Dimensions.Speaker: Andrej El (University of Frankfurt)
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Instantons and Sphalerons in a Magnetic Field 20mI study the properties of the Euclidean Dirac equation for a light fermion in the presence of both a constant abelian magnetic field and an SU(2) instanton. In particular, I analyze the zero modes analytically in various limits, both on R^4 and on the four-torus, in order to compare with recent lattice QCD results, and study the implications for the electric dipole moment of the instanton induced by the magnetic field. I also present a holographic computation of the sphaleron rate of a strongly coupled plasma in a the presence of a constant magnetic flux and discuss its various physical implications.Speaker: Gokce Basar (Stony Brook University)
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Heavy quark quenching from RHIC to LHC and the consequences of gluon damping 20mRecently, we have proposed a microscopic approach for the quenching and thermalisation of heavy quarks (HQ) in URHIC \cite{Gossiaux:2008,Gossiaux:2009,Gossiaux:2010}, assuming that they interact with light partons through both elastic and radiative processes evaluated by resorting to some parameterization of the running coupling constant, while those partons are spatially distributed along hydrodynamical evolution of the hot medium. This approach is able to explain successfully several observables measured at RHIC, such as the nuclear modification factor and the elliptic flow of non-photonic single electrons. The diffusion coefficient of heavy quarks in the quark gluon plasma -- a fundamental property of this state of matter -- can thus be extracted and compared with recent lattice calculations. In this contribution, we discuss the predictions of our model for D and B mesons production in URHIC at LHC energies and confront them with experimental results obtained so far by ALICE and CMS collaborations for Pb-Pb collisions at $\sqrt{s}=2.76~{\rm TeV}$. The slight excess of quenching found w.r.t. the D mesons data at LHC trigers our interest in new effects neglected up to now, such as the influence of gluon damping on radiative energy loss and its phenomenological consequences. In \cite{Bluhm:2011}, we have indeed studied the effect of an absorptive medium on standard LPM \cite{LPM} radiation in electrodynamics and have advocated that the large time needed for the photon formation in Bremsstrahlung from ultrarelativistic charges is not affordable if damping is taken into account. Similar effect manifests itself in QCD, as we have recently advocated in \cite{Bluhm_2012}. In our QM contribution, we intend to concentrate on the {\em implications} of such an effect on the quenching of particles in URHIC (discussing observables such as spectra, elliptic flow and azimutal correlations) as well as on the single electron puzzle. \begin{thebibliography}{9} \bibitem{Gossiaux:2008} P.B. Gossiaux, J. Aichelin, Phys. Rev. C{\bf 78}, 014904 (2008), [hep-ph/0802.2525]. \bibitem{Gossiaux:2009} P.B. Gossiaux, R. Bierkandt, J. Aichelin, Physical Review C{\bf 79} (2009) 044906 \bibitem{Gossiaux:2010} P.B. Gossiaux, V. Guiho, J. Aichelin, J. Phys. G: Nucl. Part. Phys. {\bf 37} (2010) 094019 \bibitem{Gossiaux:2011} P.B. Gossiaux et al., arXiv:1102.1114 \bibitem{Bluhm:2011} M. Bluhm, P.B. Gossiaux, and J. Aichelin, arXiv:1106.2856, PRL {\bf 107} (2011) 265004 \bibitem{LPM} L.D. Landau and I. Ya. Pomeranchuk, Dokl. Akad. Nauk SSSR {\bf 92} (1953) 535; ibid. {\bf 92} (1953) 735. \bibitem{Bluhm_2012} M. Bluhm, P. B. Gossiaux, T. Gousset, J. Aichelin,[arXiv:1204.2469v1] \end{thebibliography}Speaker: Pol Gossiaux (Subatech)
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Plenary VIB: Flash Talks Regency 2/3
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Modeling the Impact Parameter Dependence of the nPDFs With EKS98 and EPS09 Global Fits 10mThe knowledge of the parton distribution functions (PDFs) is essential for interpreting any hard-process results from hadronic and nuclear collisions. The nuclear modifications of PDFs have been successfully determined through a global DGLAP analysis e.g. in the sets EKS98 and more recently EPS09. So far the nuclear PDFs (nPDFs) in the global fits have been taken to be spatially independent. However, it can be expected that the nuclear modifications vary when going from the dense center of a nucleus to its more dilute edge. In this work, using the $A$-dependence of the globally fitted nPDFs, we have been able to determine the spatial dependence of the nPDFs in terms of powers of the nuclear thickness functions. A routine for public use is released. For applications, we will discuss how one can then compute hard-process cross sections in different centrality classes of nuclear collisions. In particular, we consider the nuclear modification factor $R_{\rm dAu}$ for neutral pion production in deuteron-gold collisions at RHIC. Comparison with the PHENIX data in different centrality classes is also shown. In addition, predictions for the corresponding nuclear modification factor $R_{\rm pPb}$ in proton-lead collisions at the LHC are discussed. Both leading-order and next-to-leading order results are considered.Speaker: Ilkka Helenius (U)
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Exploring cold nuclear matter effects in d+Au with high-pT reconstructed jets at PHENIX 10mProton-nucleus (p+A) collisions can be used to investigate cold nuclear matter effects on hard-scattered partons and serve as an important baseline for heavy-ion collisions. In particular, p+A collisions at different centrality selections can probe the impact parameter dependence of nuclear parton distribution functions, initial state energy loss and final state parton interactions in the cold nucleus. Jet reconstruction can better determine the initial parton kinematics and recent improvements in analysis techniques allow the exploration of these effects over a wide pT range. We present the latest jet reconstruction measurements performed with the PHENIX detector at RHIC in deuteron-gold (d+Au) collisions at 200 GeV using the Gaussian filter and anti-kT algorithms and discuss the possible implications on descriptions of cold nuclear matter.Speaker: Dennis Perepelitsa (Columbia University)
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Jet shapes in 2.76 TeV PbPb collisions with CMS 10mThe poster presents jet shapes, defined as the fractional transverse momentum distribution as a function of the distance r from the jet axis, where the jets are reconstructed by the anti-kT clustering algorithm. We determine the energy flow inside the jet by using particles reconstructed and calibrated using the Particle Flow algorithm. Different background subtraction methods are employed to subtract the energy not associated with the jet. The reconstructed jet shapes are corrected to the particle level using unfolding functions determined from PYTHIA+HYDJET Monte Carlo simulation. The modifications of the jet shapes due to parton-medium interactions can be studied by comparing the measurements in PbPb collision to the baseline measurements in pp collisions.Speaker: Ms Yaxian Mao (Vanderbilt University (US))
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Jet reconstruction and b-jet identification in PbPb collisions with CMS 10mThe flavor dependence of jet quenching is a powerful handle to discriminate models of parton energy loss in heavy ion collisions. While there is evidence for a strong energy loss of heavy quarks from single particle measurements, heavy flavor tagging of fully reconstructed jets has thus far not been achieved in heavy ion collisions. In this talk we demonstrate the capacity of CMS to identify jets initiated by bottom quarks using displaced vertices reconstructed in the silicon tracking system. Identification of b-jets is shown to be feasible even in the dense environment of PbPb collisions. We discuss the status and prospects for measurements of identified b-jets in PbPb collisions with CMS.Speaker: Jorge A Robles (Rutgers, State Univ. of New Jersey (US))
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Measurement of jet spectra with charged particles in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV with the ALICE detector at the LHC 10mWe report a measurement of transverse momentum spectra of jets detected with the ALICE detector in Pb-Pb collisions at $\sqrt{s_NN}$=2.76 TeV. Jets are reconstructed from charged particles using the anti-$k_{T}$ jet algorithm. The transverse momentum of tracks is measured down to 150 MeV/c which gives access to the low $p_{T}$ fragments of the jet. The background from soft particle production is determined for each event and subtracted. The remaining influence of underlying event fluctuations is quantified by embedding different probes into heavy-ion data. The reconstructed transverse momentum spectrum is corrected for background fluctuations by unfolding. We compare the inclusive jet spectra reconstructed with radii between 0.2 and 0.4 for different centrality classes and compare the jet yield in Pb-Pb and pp events.Speaker: Marta Verweij (University of Utrecht (NL))
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$\omega(782)$ and $\phi(1020)$ mesons from di-leptonic decay channels at the STAR experiment 10mHadronic resonances can play a pivotal role in providing experimental evidence for partial chiral symmetry restoration in the deconfined quark-gluon phase produced in high energy nucleus-nucleus collisions. Their lifetimes, which are comparable to the lifetime of the fireball, make them a valuable tool to study medium modifications to the resonant state due to the chiral phase transition signatures of mass shifts and/or width broadenings. This can be done via the leptonic decay of resonances with relatively small interaction of leptonic daughter particles with dense hadronic medium, however hadronic regeneration of resonances feeds into this signature as well. Particle identification based on the STAR upgraded Time-of-Flight detector in conjunction with energy-loss (dE/dx) from the Time Projection Chamber is used for a clean electron and positron identification. We will present the measurement of masses, widths, transverse momentum spectra, and yields of $\omega(782)$ and $\phi(1020)$ mesons at mid-rapidity in Au+Au collisions at \sqrts{s_{NN}} = 200 GeV and compare the $\phi(1020)$ result to those from the hadronic decay channel.Speaker: Masayuki Wada (University of Texas at Austin)
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Emission of Low Momentum Particles at Large Angles from Jet 10mHot and dense QCD matter, namely the quark gluon plasma, is created in high energy heavy ion collisions. High energy partons are also created through initial hard scatterings and have to traverse the QGP medium. These energetic partons are subject to lose their energy due to strong interactions with the medium. So jets in heavy ion collisions are expected to give information about the stopping power of the QGP. While jets traverse the QGP medium, they could induce collective flow in the fluid by depositing energy and momentum. Thus the space-time evolution of the QGP fluid would be affected when jets pass through the medium. In fact, the CMS Collaboration observed a lot of low momentum hadrons at large angles from a quenched jet [1]. These low momentum hadrons are intimately related with jet energy loss since the total momentum of these hadrons together with the quenched jet balances the momentum of the other jet propagating in the opposite direction. The CMS result can be interpreted as manifestation of a wake of the QGP fluid by jet energy loss. In this study, we construct a model to describe the dynamics of QGP fluid and jets simulta- neously. We model a source term in the relativistic hydrodynamic equations which originates from the energy and momentum deposited from traversing jets. Without linearization we solve these non-linear hydrodynamic equations numerically in fully three dimensional space and describe the dynamics of the background QGP medium. A Mach cone like structure and a vortex ring appear behind the jet traversing a uniform medium. When a pair of jets go through a fluid expanding three dimensionally, the Mach cone like structure is distorted by radial flow. As a result, low momentum particles from the medium are preferentially emitted at large angles from the jet axis. The result exhibits the same trend as the one observed by the CMS Collaboration. References [1]S. Chatrchyan et al. [CMS Collaboration], Phys. Rev. C 84, 024906 (2011); C. Roland, J. Phys. G 38, 124020 (2011) . [2]Y. Tachibana, “A Relativistic Hydrodynamic Model with Source Terms and its Application to Heavy Ion Collisions,” Master thesis, the Univ. of Tokyo (2012).Speaker: Mr Yasuki Tachibana (Department of Physics, The University of Tokyo)
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Hydrodynamic Fluctuations and Two‐Particle Correlations 1mWe investigate contributions from local hydrodynamic fluctuations to the near side ridge in the two‐particle correlation data from heavy ion collisions. We introduce a local perturbation on top of a hydrodynamic flow which respects conformal symmetry and incorporates radial flow. The subsequent evolution of the perturbation is determined by hydrodynamics; after freeze‐out, we examine the effects this local perturbation on the single particle spectrum, as well as the angular and rapidity dependence of the two‐particle correlation function. We hope that our analytical results in this physical system with enhanced symmetries will provide guidance to those wishing to incorporate flow fluctuationsSpeaker: Todd Springer (U)
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Coffee Break 29m
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Plenary VIC: Rapporteur Talks (Chair W. Busza) Regency 2/3
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Rapporteur Talk: Heavy Flavor, Quarkonia and Electroweak Probes 30mSpeakers: Charles Gale (McGill University), Lijuan Ruan
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Plenary VID: Awards Regency 2/3
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