# Quark Matter 2012

US/Eastern
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).

• Student day will take place on Sunday, August 12, 2012
• Nuclear Physics A will be sponsoring a NPA Young Scientist Award at QM'12
• Sunday, 12 August
• 9:00 AM 12:30 PM
Student's Day A (Chair S. Bass) Palladian

• 9:00 AM
The QCD Phase Diagram 1h Palladian

Speaker: Prof. Misha Stephanov (UIC)
• 10:00 AM
Coffee Break 30m Bird Cage

### Bird Cage

• 10:30 AM
Small-x Physics and Saturation 1h Palladian

Speaker: Javier Lopez Albacete (IPhT-CEA)
• 11:30 AM

Speaker: Paul Sorensen (BNL)
• 12:30 PM 1:30 PM
Student Lunch 1h
• 1:00 PM 3:30 PM
Teacher's Day Empire

### Empire

• 1:00 PM
Visualizing the "little bangs": Simulations and visualizations of relativistic heavy ion collisions 40m
Speaker: Hannah Petersen
• 1:40 PM
Peering through the haze: Reconstructing the QGP's properties 55m
Speaker: Mike Lisa (Ohio State University (US))
• 2:35 PM
Unexpected connections: Hot quark matter, black holes, and superstring theory 40m
Speaker: Paul Chesler (MIT)
• 3:15 PM
Break 15m
• 1:30 PM 3:30 PM
Student Day B (Chair G. Roland) Palladian

• 1:30 PM
Hydro & Transport 1h
Speaker: Dr Bjoern Schenke (Brookhaven National Lab)
• 2:30 PM
Hard Probes 1h
Speaker: Yen-Jie Lee (CERN)
• 3:30 PM 4:30 PM
Student and Teacher Joint Session (Chair R. Venugopalan) Palladian

• 3:30 PM
Quest for the QGP 1h
Speaker: Bill Zajc (Columbia University)
• 4:30 PM 5:15 PM
Student and Teacher Reception 45m
• 5:15 PM 10:00 PM
Conference Registration
• 5:15 PM 6:15 PM
Student's Day C (Chair R. Venugopalan) Palladian

• 5:15 PM
Proton-Nucleus collisions at LHC and Electron-Nucleus collisions at an EIC 1h
Speaker: Nestor Armesto Perez (Universidade de Santiago de Compostela (ES))
• Monday, 13 August
• 7:30 AM 8:30 AM
Conference Registration (All day)
• 8:30 AM 10:15 AM
Plenary IA: Opening Session (Chairs: J. Harris, D. Kharzeev, T. Ullrich) Regency 2/3

### Regency 2/3

• 8:30 AM
Welcome 30m
• 9:00 AM
Speaker: Bart Gordon
• 9:30 AM
Speaker: Urs Wiedemann (CERN)
• 10:15 AM 10:45 AM
Coffee Break 30m Bird Cage & Regency Gallery

### Bird Cage & Regency Gallery

• 10:45 AM 12:50 PM
Plenary IB: Experimental Highlights (Chair: J. Stachel) Regency 2/3

### Regency 2/3

• 10:45 AM
PHENIX Highlights 25m
Speaker: Takao Sakaguchi (BNL)
• 11:10 AM
STAR Highlights 25m
Speaker: Xin Dong (LBNL)
• 11:35 AM
Overview of recent ALICE results 25m
Speaker: Karel Safarik (CERN)
• 12:00 PM
ATLAS Highlights 25m
Speaker: Barbara Krystyna Wosiek (Polish Academy of Sciences (PL))
• 12:25 PM
Experimental highlights from the CMS Collaboration 25m
Speaker: Gunther Roland (Massachusetts Inst. of Technology (US))
• 12:50 PM 2:15 PM
Lunch 1h 25m Blue Room

### Blue Room

• 2:15 PM 4:20 PM
Plenary IC: Initial State, Global & Collective Dynamics (Chair: L. McLerran) Regency 2/3

### Regency 2/3

• 2:15 PM
Review of CGC & Developments 25m
Speaker: Adrian Dumitru (Baruch College (City University of New York))
• 2:40 PM
Initial-state fluctuations to Final State Physics 25m
Speaker: Kevin Dusling
• 3:05 PM
PHENIX Results on Cold Nuclear Matter 25m
Speaker: Matthew Wysocki (University of Colorado at Boulder)
• 3:30 PM
Hydro Overview 25m
Speaker: Dr Jean-Yves Ollitrault (CNRS)
• 3:55 PM
Azimuthal Anisotropy Results from STAR 25m
Speaker: Daniel Cebra (UC Davis)
• 4:20 PM 4:50 PM
Refreshment Break 30m Bird Cage & Regency Gallery

### Bird Cage & Regency Gallery

• 4:50 PM 6:30 PM
Plenary ID: Initial State, Global & Collective Dynamics (Chair: B. Jacak) Regency 2/3

### Regency 2/3

• 4:50 PM
Results on flow from ALICE 25m
Speaker: Sergey Voloshin (Wayne State University (US))
• 5:15 PM
Overview of results on flow and correlations from the CMS collaboration 25m
This 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))
• 5:40 PM
ATLAS Flow & Correlations 25m
• 6:05 PM
Extraction of transport coefficients 25m
Speaker: Huichao Song
• 7:30 PM 10:00 PM
Reception - Luce Center of the Smithsonian American Art Museum 2h 30m Smithsonian Museum

#### Smithsonian Museum

• Tuesday, 14 August
• 8:30 AM 10:45 AM
Plenary IIA: Jets (Chair M. Gyulassy) Regency 2/3

### Regency 2/3

• 8:30 AM
Theoretical overview of jet quenching 20m
Speaker: Guilherme Teixeira De Almeida Milhano (Instituto Superior Tecnico (PT))
• 8:50 AM
ATLAS Jets 20m
Speaker: Martin Spousta (Columbia University and Charles University)
• 9:10 AM
Results on jet spectra and structure from ALICE 20m
Speaker: Dr Andreas Morsch (CERN)
• 9:30 AM
Overview of results on jets from the CMS collaboration 20m
Speaker: Dr Gabor Veres (CERN)
• 9:50 AM
PHENIX High pT 20m
Speaker: Michael McCumber (University of Colorado)
• 10:10 AM
Results on identified particle spectra from ALICE 20m
Speaker: Marian Ivanov (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
• 10:30 AM
Jet Discussion 15m
• 10:45 AM 11:15 AM
Coffee Break 30m Bird Cage & Regency Gallery

### Bird Cage & Regency Gallery

• 11:15 AM 12:50 PM
Plenary IIB: Heavy Flavor (Chair: P. Giubellino) Regency 2/3

### Regency 2/3

• 11:15 AM
Heavy Flavor Results from STAR 20m
Speaker: Wei Xie (Purdue University (US))
• 11:35 AM
PHENIX Heavy Flavors 20m
Speaker: Prof. Marzia Rosati (Iowa State University)
• 11:55 AM
Results on heavy flavors from ALICE 20m
Speaker: Zaida Conesa Del Valle (CERN)
• 12:15 PM
Heavy quark production and energy loss 20m
Speaker: William Horowitz (University of Cape Town)
• 12:35 PM
Heavy Flavor Discussion 15m
• 12:50 PM 1:05 PM
Conference Photo 15m
• 1:05 PM 2:15 PM
Lunch 1h 10m Blue Room

#### Blue Room

• 2:15 PM 4:15 PM
Parallel 1A: Global & Collective Dynamics (Chair U. Heinz) Regency 2/3

### Regency 2/3

• 2:15 PM
Shocks in Quark-Gluon Plasma 20m
Large 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)
• 2:35 PM
PHENIX Measurements of Higher-order Flow Harmonics for Identified Charged Hadrons in Au+Au Collisions at 39 – 200 GeV 20m
Collective 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)
• 2:55 PM
Beam Energy Dependence of First and Higher-Order Flow Harmonics from the STAR Experiment at RHIC 20m
A 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)
• 3:15 PM
Collision Energy Dependence of Viscous Hydrodynamic Flow in Relativistic Heavy-Ion Collisions 20m
We 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)
• 3:35 PM
Non-linear anisotropic flow with ideal and viscous hydrodynamics 20m
The 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)
• 3:55 PM
Derivation of transient relativistic fluid dynamics from the Boltzmann equation for a multi-component system 20m
We 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)
• 2:15 PM 4:15 PM
Parallel 1B, Jets (Chair X.N. Wang) Palladian

• 2:15 PM
Study of jet quenching using photon-jet events in PbPb collisions at 2.76 TeV with CMS 20m
The 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))
• 2:35 PM
Study of correlations between neutral bosons and jets in lead-lead collisions at 2.76 TeV with the ATLAS detector 20m
The 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))
• 2:55 PM
Prompt Photon Production and Photon-Jet Hadron Correlations in PHENIX at RHIC 20m
A 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))
• 3:15 PM
Correlation between isolated photons and charged hadrons in pp and Pb-Pb collisions measured with ALICE 20m
Gamma-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))
• 3:35 PM
Electroweak boson-tagged jet event asymmetries at the Large Hadron Collider 20m
Tagged 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)
• 2:15 PM 4:15 PM
Parallel 1C: Correlations & Fluctuations (Chair J. Schukraft) Diplomat

### Diplomat

• 2:15 PM
Detailed HBT measurement with respect to event plane and collision energy in Au+Au collisions at PHENIX 20m
The 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)
• 2:35 PM
Femtoscopy of identified particles at STAR. 20m
Measurement 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)
• 2:55 PM
Meson and baryon femtoscopy in heavy-ion collisions at ALICE 20m
In 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))
• 3:15 PM
Short- and long-range very-high-pT triggered dihadron correlations in PbPb collisions at 2.76 TeV with CMS 20m
New 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))
• 3:35 PM
Event shape engineering with ALICE 20m
Strong 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))
• 3:55 PM
Azimuthal anisotropy of charged hadrons at very high pT in PbPb collisions at 2.76 TeV with CMS 20m
Measurements 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))
• 2:15 PM 4:15 PM
Parallel 1D: Heavy Flavor & Quarkonia (Chair R. Granier de Cassagnac) Empire

### Empire

• 2:15 PM
Detailed measurements of charmonium suppression in PbPb collisions at 2.76 TeV with CMS 20m
CMS 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))
• 2:35 PM
Jpsi and psi (2S) production in Pb-Pb collisions with the ALICE Muon spectrometer at the LHC 20m
ALICE 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))
• 2:55 PM
Heavy quark potential at non-zero temperature and quarkonium spectral functions 20m
We 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)
• 3:15 PM
Recent Heavy Quarkonia Results from PHENIX 20m
The 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)
• 3:35 PM
Quarkonia production in the STAR experiment 20m
The 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)
• 3:55 PM
Comprehensive Analysis of in-Medium Quarkonia from SPS to LHC 20m
We 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)
• 4:15 PM 4:45 PM
Coffee Break 30m Bird Cage & Regency Gallery

### Bird Cage & Regency Gallery

• 4:45 PM 6:30 PM
Parallel 2A: Global & Collective Dynamics (Chair A. Poskanzer) Regency 2/3

### Regency 2/3

• 4:45 PM
Measurement of elliptic and higher-order harmonics at 2.76 TeV Pb-Pb collisions with the ATLAS detector 20m
Anisotropy 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))
• 5:05 PM
Shear viscosity of the quark-gluon plasma from flow in heavy-ion collisions 20m
We 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)
• 5:25 PM
Pseudorapidity density of charged particles in a wide pseudorapidity range and its centrality dependence in Pb-Pb collisions at 2.76 TeV 20m
In 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))
• 5:45 PM
Pseudorapidity and centrality dependence of transverse energy flow in PbPb collisions at 2.76 TeV from CMS 20m
The 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))
• 6:05 PM
E-by-E MUSIC Afterburner 20m
Hydrodynamic 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)
• 4:45 PM 6:30 PM
Parallel 2B: Jets (Chair P. Jacobs) Palladian

• 4:45 PM
Studies of jet quenching and b-jet tagging in PbPb collisions at 2.76 TeV with CMS 20m
This 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))
• 5:05 PM
Measurements of jet suppression with ATLAS 20m
The 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))
• 5:25 PM
Inclusive jet and charged hadron nuclear modification factors in PbPb collisions at 2.76 TeV with CMS 20m
Measurements 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))
• 5:45 PM
Quantifying a Possibly Reduced Jet-Medium Coupling of the sQGP at the Large Hadron Collider 20m
Recent 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)
• 6:05 PM
Inclusive jet spectra in 2.76 TeV Pb-Pb collisions from the ALICE experiment 20m
Measurements 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))
• 4:45 PM 6:30 PM
Parallel 2C: Correlations & Fluctuations (Chair X. Dong) Diplomat

### Diplomat

• 4:45 PM
Search for QCD Phase Transitions and the Critical Point Utilizing Particle Ratio Fluctuations and Transverse Momentum Correlations from the STAR Experiment. 20m
Dynamical 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)
• 5:05 PM
Studies of net-charge fluctuations and balance functions with the ALICE detector at the LHC 20m
The 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))
• 5:25 PM
Study of the Sixth Order Cumulant of Net-proton Distributions Measured in STAR at RHIC 20m
In 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)
• 5:45 PM
Mixed harmonic charge dependent azimuthal correlations in Pb-Pb collisions at 2.76TeV measured with the ALICE experiment at the LHC 20m
The 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))
• 6:05 PM
Charge balancing and the fall off of the ridge 20m
The 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
• 4:45 PM 6:30 PM
Parallel 2D: Heavy Flavor & Quarkonia (Chair J.-P. Blaizot) Empire

### Empire

• 4:45 PM
Detailed measurements of bottomonium suppression in PbPb collisions at 2.76 TeV with CMS 20m
The 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))
• 5:05 PM
Momentum dependences of charmonium properties from lattice QCD 20m
We 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 Speaker: Heng-Tong Ding (Brookhaven National Lab) • 5:25 PM J/psi production at mid-rapidity in Pb-Pb collisions at 2.76 TeV 20m The 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)) • 5:45 PM Gluon saturation effects on the color singlet J/Psi production in high energy dA and AA collisions 20m We 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) • 6:05 PM High transverse momentum quarkonium production and dissociation in heavy ion collisions 20m We 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_TJ/\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$in the most central nuclear reactions suggests the presence of thermal effects at the level of the quarkonium wavefunction, even at large transverse momentum. Speaker: Dr Rishi Sharma (TRIUMF) • 7:00 PM 8:00 PM Energy for the 21st Century World Economy: Problems and Opportunities 1h Regency 2/3 ### Regency 2/3 Speaker: Prof. Wolfgang Bauer (Distinguished University Professor, Michigan State University) • Wednesday, 15 August • 8:30 AM 10:30 AM Parallel 3A: Global & Collective Dynamics (Chair T. Kodama) Regency 2/3 ### Regency 2/3 • 8:30 AM Bulk viscosity, particle spectra and flow in heavy-ion collisions 20m We study the effects of bulk viscosity on$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) • 8:50 AM Initial state fluctuations and higher harmonic flow in heavy-ion collisions 20m We 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 • 9:10 AM Higher harmonics flow measurement of charged hadrons and electrons in wide kinematic range with PHENIX VTX tracker 20m Collective 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) • 9:30 AM Two- and Multi-particle cumulant measurements of vn and isolation of flow and nonflow in 200 GeV Au+Au Collisions by STAR 20m Azimuthal 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) • 9:50 AM Study of higher harmonics based on (3+1)-dimensional relativistic viscous hydrodynamics 20m Currently 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) • 10:10 AM Systematic Investigation of Partonic Collectivity through Centrality Dependence of Elliptic Flow of Multi-strange Hadrons in Au+Au collisions at 200 GeV in STAR 20m One 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$and$pv_{2}$measurements at the low transverse momentum ($p_{T}$). Speaker: Mr NASIM MD (Variable Energy Cyclotron Centre) • 8:30 AM 10:30 AM Parallel 3B: Jets (Chair S. Mioduszewski) Palladian ### Palladian • 8:30 AM Understanding LHC jets in the light of RHIC data 20m Hard 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) • 8:50 AM Jet structure in 2.76 TeV Pb–Pb collisions at ALICE 20m To 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) • 9:10 AM Jet shapes in pp and PbPb collisions at the CMS Experiment 20m Jet 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)) • 9:30 AM Jet fragmentation and jet properties in 2.76 TeV Pb+Pb collisions using the ATLAS Detector at LHC 20m The 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)) • 9:50 AM Jet fragmentation functions in PbPb and pp collisions at 2.76 TeV with CMS 20m The 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)) • 10:10 AM Medium-induced soft gluon distribution inside a jet 20m The 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) • 8:30 AM 10:30 AM Parallel 3C: Electro-Weak Probes (Chair J. Kapusta) Diplomat ### Diplomat • 8:30 AM Thermal dileptons in high-energy heavy ion collisions with 3+1D relativistic hydrodynamics 20m The 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) • 8:50 AM Dielectron measurements by PHENIX using the HBD 20m Measurements 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$Dalitz decays. It was successfully operated in RHIC run years 2009 to 2010, where Au+Au and reference p+p data sets were taken. We will present the dielectron results from the analysis of these data sets. Speaker: Dr Ermias Atomssa (Stony Brook University) • 9:10 AM Di-electron differential cross section in Au+Au collisions at different beam energies at STAR 20m Di-leptons serve as clean and bulk penetrating probes to study the properties of the strongly interacting hot and dense medium created in heavy ion collisions. They are produced in all stages of the heavy-ion collisions and are not affected by strong interactions, hence can probe the entire evolution of the collision. Di-lepton production in the low mass range ($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
Speaker: Dr Huang Bingchu (Brookhaven National Lab)
• 9:30 AM
Jet-Tagged Back-Scattering Photons For Quark Gluon Plasma Tomography 20m
We 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)
• 9:50 AM
Measurement of direct photons in pp and Pb-Pb collisions with ALICE 20m
Direct 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))
• 8:30 AM 10:30 AM
Parallel 3D: Pre-Equilibrium & Initial State (Chair K. Eskola) Empire

### Empire

• 8:30 AM
Studies of the nuclear stopping power in PbPb collisions at 2.76 TeV with CMS 20m
The 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))
• 8:50 AM
Highly-anisotropic hydrodynamics in 3+1 space-time dimensions and the early thermalization puzzle 20m
Speakers: Michael Strickland (Gettysburg College) , Wojciech Florkowski (Institute of nuclear Physics, Krakow)
• 9:10 AM
Azimuthal angular correlations in two-particle production in proton-nucleus collisions 20m
Di-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)
• 9:30 AM
Cold Nuclear Matter Effects in 200 GeV d+Au Collisions at PHENIX 20m
While 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
• 9:50 AM
Jet probes of cold and hot QCD matter 20m
Parton 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)
• 10:10 AM
Gravitational collapse and holographic thermalization 20m
A 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)
• 8:30 AM 10:30 AM
Poster Viewing Regency 1/3 and Ambassador

• 10:30 AM 11:00 AM
Coffee Break 30m Bird Cage & Regency Gallery

### Bird Cage & Regency Gallery

• 11:00 AM 12:40 PM
Parallel 4A: Global & Collective Dynamics (Chair P. Sorenson) Regency 2/3

### Regency 2/3

• 11:00 AM
Deviation from quark number scaling of the anisotropy parameter v2 of pions, kaons, and protons in Au+Au collisions at 200 GeV 20m
The 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)
• 11:20 AM
Measurement of dipole flow associated with initial geometry fluctuations in Pb-Pb collisions with the ATLAS detector 20m
A 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)
• 11:40 AM
Baryon anomaly in heavy-ion collisions and colour correlations in QGP 20m
A 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)
• 12:00 PM
Midrapidity antibaryon-to-baryon ratios in pp and Pb-Pb collisions measured by the ALICE experiment 20m
The 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)) • 12:20 PM Late Result - Ds RAA from ALICE 20m The 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)) • 11:00 AM 12:20 PM Parallel 4B: Jets (Chair N. Armesto) Palladian ### Palladian • 11:00 AM Jet-medium interactions in Pb-Pb collisions 20m Previous 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)) • 11:20 AM Study of jet fragmentation with particle correlations in Pb-Pb collision at 2.76 TeV by ALICE 20m A 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}$) in central \pbpb\ collisions at \snn=2.76 \tev\ which may be also interpreted as a hint of the modification of the fragmentation function due to induced gluon radiation. In order to study further the nature of the intra-jet correlation yield enhancement an analysis of the jet-fragmentation transverse momentum was performed. Modification of this distribution with the centrality of the collision will be presented. A possible path length dependency of the induced radiation is studied using a comparison of the two-particle correlation for different orientations of the trigger particle with respect to the event plane and comparing the jet-fragmentation transverse momentum distribution measured in different event-by-event anisotropy classes. Speaker: Filip Krizek (Helsinki Institute of Physics (FI)) • 11:40 AM Measurements of the Correlation between Jets and the Reaction Plane in STAR at RHIC 20m The relationship between jet properties and the underlying geometry of the medium produced in heavy ion collisions can be explored through a measurement of the correlation between the axes of reconstructed jets and the reaction plane (defined as jet$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) • 12:00 PM Neutral meson production in pp and Pb-Pb collisions at the LHC measured with ALICE 20m Identified 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)) • 11:00 AM 12:20 PM Parallel 4C: Electro-Weak Probes (Chair D. D'Enterria) Diplomat ### Diplomat • 11:00 AM Measurement of isolated direct photons in lead-lead collisions at 2.76 TeV with the ATLAS detector 20m Direct 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)) • 11:20 AM Inclusive isolated photons in pp and PbPb collisions at 2.76 TeV with CMS 20m Final 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)) • 11:40 AM Measurements of W and Z boson production in Pb+Pb collisions at 2.76 TeV with the ATLAS detector. 20m Collisions 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)) • 12:00 PM Z and W boson production in PbPb collisions at 2.76 TeV with CMS 20m The 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)) • 11:00 AM 12:40 PM Parallel 4D: Pre-Equilibrium & Initial State (Chair T. Ludlam) Empire ### Empire • 11:00 AM Multigluon correlations in the color glass condensate 20m Multiparticle 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) • 11:20 AM Effect of longitudinal fluctuation in event-by-event (3+1)D hydrodynamics 20m Hadron 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) • 11:40 AM Imprinting quantum fluctuations on hydrodynamic initial conditions 20m The 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) • 12:00 PM The spectrum of quantum fluctuations and space-time evolution in the little bang 20m We 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) • 12:20 PM Forward azimuthal correlations in 200 GeV p+p and d+Au collisions at STAR 20m The 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 Speaker: Xuan Li (Shandong University) • 11:00 AM 6:00 PM Poster Viewing Regency 1/3 and Ambassador ### Regency 1/3 and Ambassador • 12:40 PM 6:00 PM Lunch time and afternoon free for discussions and excursions 5h 20m • Thursday, 16 August • 8:30 AM 10:10 AM Plenary IVA: Real & Virtual Photons (Chair: T. Nayak) Regency 2/3 ### Regency 2/3 • 8:30 AM Di-Lepton Physics Program at STAR 25m Speaker: Frank Geurts (Rice University (US)) • 8:55 AM PHENIX Low Mass Di-leptons 25m Speaker: Itzhak Tserruya (Weizmann Institute of Science (IL)) • 9:20 AM Photons and electroweak probes in ATLAS 25m Speaker: Peter Alan Steinberg (Brookhaven National Laboratory (US)) • 9:45 AM Overview of results on photon and electroweak boson production from the CMS collaboration 25m Speaker: Raphael Granier De Cassagnac (Ecole Polytechnique (FR)) • 10:10 AM 10:25 AM Award of Zimanyi Award (Chair M. Gyulassy) 15m • 10:25 AM 11:05 AM Coffee Break 40m • 11:05 AM 12:45 PM Plenary IVB: Quarkonia, Real & Virtual Photons (Chair Y. Schutz) Regency 2/3 ### Regency 2/3 • 11:05 AM Overview of results on heavy flavor and quarkonia from the CMS collaboration 20m Speaker: Camelia Mironov (Ecole Polytechnique (FR)) • 11:25 AM Results on quarkonia from ALICE 20m Speaker: Enrico Scomparin (Universita e INFN (IT)) • 11:45 AM Heavy quarkonium in hot medium 20m Speaker: Tetsuo Hatsuda (Unknown) • 12:05 PM Quarkonia Discussion 15m • 12:20 PM Search for Chiral Magnetic Effects in High-Energy Nuclear Collisions 25m Speaker: Gang Wang (UCLA) • 12:45 PM 2:00 PM Lunch 1h 15m Blue Room #### Blue Room • 2:00 PM 4:00 PM Parallel 5A: Hadron Thermodynamics and Chemistry (Chair R. Stock) Regency 2/3 ### Regency 2/3 • 2:00 PM Identified charged hadron production at the LHC with the ALICE experiment 20m Identified 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)) • 2:20 PM The statistical model in Pb-Pb collisions at the LHC 20m We 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)) • 2:40 PM Strange hadrons and resonances in Pb-Pb collisions at sqrt_NN = 2.76 TeV with ALICE experiment at LHC 20m The 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)) • 3:00 PM Beam Energy Dependence of Strange Hadron Production from STAR at RHIC 20m Strange 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) • 3:20 PM (Anti) matter and hyper-matter production at the LHC with the ALICE experiment 20m The 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)) • 3:40 PM Beam Energy Dependence of Hypertriton Production and Lifetime Measurement at STAR 20m The 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:1203.2547v1 Speaker: Ms Yuhui Zhu (Shanghai Institute of Applied Physics) • 2:00 PM 4:00 PM Parallel 5B: QCD at Finite Temperature and Density (Chair F. Karsch) Palladian ### Palladian • 2:00 PM Photon production in hot QCD plasmas at NLO and two-to-three processes 20m We 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) • 2:20 PM Transverse Momentum Broadening in Weakly Coupled Quark-Gluon Plasma 20m We 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) • 2:40 PM Electric and baryonic charge fluctuations from lattice QCD 20m We 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) • 3:00 PM Lattice QCD thermodynamics in the presence of the charm quark 20m We 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) • 3:20 PM Freeze-out conditions from lattice QCD 20m Traditionally 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) • 3:40 PM The QCD Equation of State with 2+1 flavors of Highly Improved Staggered Quarks 20m The 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) • 2:00 PM 4:00 PM Parallel 5C: High pt and Jets (Chair B. Cole) Diplomat ### Diplomat • 2:00 PM Systematic Monte-Carlo studies of dijets at the LHC and RHIC 20m Recent 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) • 2:20 PM Production of Charged Pions, Kaons, and Protons in 2.76 TeV Pb-Pb Collisions at high p_t measured with the ALICE Experiment. 20m The 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)) • 2:40 PM Charged particle spectra and nuclear modification factor in lead-lead collisions at 2.76 TeV with the ATLAS detector at the LHC. 20m The 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)) • 3:00 PM 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 20m The 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}$suppression in nuclear collisions. Speaker: Evan Sangaline (UC Davis) • 3:20 PM Strange hadrons at intermediate and high transverse momentum in p+p, d+Au, Cu+Cu and Au+Au collisions at 200 GeV measured with PHENIX detector 20m The hadrons containing strange quark(s) are among the most interesting probes of the hot and dense matter produced in heavy ion collisions at Relativistic Heavy Ion Collider (RHIC). While p+p collisions are used as a baseline for comparison with heavier collision systems and provide a cross check for pQCD calculations, d+Au collisions are used to study cold nuclear matter effects for mesons and baryons and their dependence on particle mass and flavor. Heavy ion collisions provide an insight into effects of quark recombination and jet quenching. Experimental measurements reveal if strange particles are suppressed at high transverse momentum ($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$range for p+p, d+Au, Cu+Cu and Au+Au collisions at \sqrt{s_{NN}} = 200 GeV. The nuclear modification factors are obtained for d+Au and heavy ion collisions at different centralities. These systematic study advance the understanding of the strange meson and baryon production and their difference from light hadrons. Speaker: Dr Prashant Shukla (Bhabha Atomic Research Centre (IN)) • 3:40 PM A Running Coupling Explanation of the Surprisingly Transparency of the QGP at LHC 20m The CUJET1.0 Monte Carlo Jet Energy loss model is applied to predict the jet flavor, centrality and density dependence of the nuclear modification factor$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}$data from ALICE, ATLAS, and CMS. (Ref: 1: W.H.Horowitz et al, NPA872(2011)265, A.Buzzatti et al, PRL108(2012)022301, B.Betz et al arXiv:1201.0281 [nucl-th]) Speaker: Alessandro Buzzatti (Columbia University) • 2:00 PM 4:00 PM Parallel 5D: New Theoretical Developments (Chair B. Sinha) Empire ### Empire • 2:00 PM Calculating Jet Transport Coefficients in Lattice Gauge Theory 20m The in-medium modification of a hard jet is reformulated to consider the process of a hard parton propagating through a finite sized QCD medium, held at a fixed high temperature and vanishing chemical potential. The process is factorized into a hard part representing the propagation and scattering of the parton, and a soft part representing the non-perturbative color field experienced by the jet in the medium. A series of such non-perturbative, soft, transport coefficients are identified, and formulated in terms of well defined operator products. These operator products are then expanded in a series of power suppressed local operators, which are then evaluated non-perturbatively using quenched lattice gauge theory. Speaker: Dr Abhijit Majumder (Wayne State University) • 2:20 PM A Non-AdS/CFT bound on eta/s 20m Hydrodynamics predicts long-lived sound and shear waves. Thermal fluctuations in these waves can lead to the diffusion of momentum density, contributing to the shear viscosity and other transport coefficients. Within viscous hydrodynamics in 3+1 dimensions, this leads to a positive contribution to the shear viscosity, which is finite but inversely proportional to the microscopic shear viscosity. Therefore the effective infrared viscosity is bounded from below. The contribution to the second-order transport coefficient$\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$. Speaker: Paul Romatschke (FIAS Frankfurt) • 2:40 PM Coupling dependence of jet quenching in hot strongly-coupled gauge theories 20m Previous top-down studies of jet stopping in strongly-coupled QCD-like plasmas with gravity duals have been in the infinite 't Hooft coupling limit$\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) • 3:00 PM Shining a Gluon Beam through Quark-Gluon Plasma 20m A 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) • 3:20 PM Color decoherence of jets in Heavy Ion Collisions 20m The 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
Speaker: Dr Yacine Mehtar-Tani (IPhT-Saclay)
• 3:40 PM
Temperature dependence of the shear viscosity in the semi-QGP 20m
An 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.)
• 4:00 PM 6:00 PM
Poster Session Reception 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.

• 4:00 PM
"Chemical" composition of the Quark-Gluon Plasma in relativistic heavy-ion collisions 2h
We 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)
• 4:00 PM
${\rm D^+}$ meson production in p-p and Pb-Pb collisions with the ALICE detector 2h
Open 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))
• 4:00 PM
A chiral effective theory for dilepton production in NN and AA collisions 2h
In 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)
• 4:00 PM
A detailed study of open heavy flavor production, enhancement, and suppression at RHIC 2h
The 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)
• 4:00 PM
A direct measure of anisotropic velocity in relativistic heavy ion collisions 2h
The 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)
• 4:00 PM
A GEM-based continuous readout scheme for the ALICE TPC 2h
The 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))
• 4:00 PM
A novel high momentum particle identification detector for the next generation ALICE experiment 2h
A 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))
• 4:00 PM
A QCD-like theory with the Z_{Nc} symmetry 2h
We 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)
• 4:00 PM
Conceived 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)
• 4:00 PM
A Study of High-pT/High-mass Dielectron Production through Trigger Combination in 200 GeV Au+Au Collisions at STAR 2h
Dileptons 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))
• 4:00 PM
A Technique for Charm and Beauty Separation via DCA Unfolding 2h
The 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)
• 4:00 PM
A way to acquire some current quark mass from a general relativistic effect 2h
We 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)
• 4:00 PM
An extreme granularity electromagnetic calorimeter using monolithic pixels for future forward measurements in ALICE 2h
A 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)
• 4:00 PM
Analysis of the pi0-charged hadron correlations using ALICE EMCal 2h
Neutral 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))
• 4:00 PM
Anisotropic flow in event-by-event ideal hydrodynamic simulations of √sNN=200 GeV Au+Au collisions 2h
We 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:1203.2882
Speaker: Dr Frederique Grassi (Universidade de Sao Paulo, Brazil)
• 4:00 PM
Anisotropic flow of φ meson in Pb-Pb collisions at sqrt{s_{NN}} = 2.76 TeV with the ALICE detector 2h
The $\phi$-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))
• 4:00 PM
Anisotropic optical response of dense quark matter under rotation - compact stars as cosmic polarizers - 2h
Quantum 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)
• 4:00 PM
Anomalous soft photon production from QCD vacuum polarization 2h
Anomalous 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)
• 4:00 PM
Antiparticle to particle ratios and identified hadron spectra for p+p collisions in sqrt(s)=62.4 GeV at STAR 2h
Information 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)
• 4:00 PM
Assessment of heavy-ion background fluctuations via Independent Particle Emission in full jet reconstruction measurements 2h
The 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)
• 4:00 PM
Azimuthal angle correlations in forward dihadron production in pA collisions 2h
Single 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)
• 4:00 PM
Azimuthal angular correlations between heavy flavour decay electrons and charged hadrons in pp collisions at 2.76 TeV with the ALICE experiment 2h
The 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))
• 4:00 PM
Azimuthal anisotropy harmonics in ultra-central PbPb collisions at 2.76 TeV from the CMS experiment 2h
Azimuthal 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)
• 4:00 PM
Azimuthal Correlation of Charm at Large Hadron Collider 2h
We 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)
• 4:00 PM
Background-subtraction procedure for the measurement of the elliptic flow of heavy-flavour decay electrons in ALICE 2h
In 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.)
• 4:00 PM
Balance function studies for non–identified particles in Pb–Pb collisions at √sNN = 2.76 TeV 2h
The 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))
• 4:00 PM
Baryon number probability distribution in the presence of the chiral phase transition 2h
We 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)
• 4:00 PM
Baryonic resonances at the LHC energies with the ALICE experiment 2h
The 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))
• 4:00 PM
Beam Energy Dependent Charge Balance Functions in Heavy Ion Collisions at STAR 2h
The 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)
• 4:00 PM
Bulk properties of hot QCD matter at RHIC and LHC and Universal QGP hadronization condition 2h
The 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))
• 4:00 PM
Can baryon stopping explain the breakdown of constituent quark scaling and proposed signals of chiral magnetic waves at RHIC? 2h
Azimuthal 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)
• 4:00 PM
Can falling strings in deformed AdS geometries account for the surprising transparency of the sQGP at LHC? 2h
We 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)
• 4:00 PM
Centrality and pT dependence study of Dielectron Production in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at STAR 2h
Dilepton 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)
• 4:00 PM
Centrality, mass and transverse momentum dependence of di-electron elliptic flow in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at STAR 2h
Di-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 ($1.1 Speaker: Xiangli Cui (U) • 4:00 PM Charge Asymmetry Dependency of$\pi^+/\pi^-$Azimuthal Anisotropy in Au + Au Collisions at STAR 2h A recent theoretical study indicates that a chiral magnetic wave at finite baryon density could induce an electric quadrupole moment in the quark-gluon plasma produced in heavy ion collisions. The quadrupole deformation will lead to a difference in azimuthal anisotropy$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^-$will be shown as a function of net charge asymmetry and centrality. In addition, these results will be compared with model calculations. Speaker: Hongwei Ke (Central China Normal University) • 4:00 PM Charge azimuthal correlations at RHIC and LHC energies 2h With a multi-phase transport model including initial charge separation and string melting, the charge azimuthal correlations for Au+Au collisions at center of mass energies 200, 39, 11.5, 7.7 GeV and Pb+Pb collisions at 2.76 TeV are investigated. Initial charge separations of about 10 % for 200 GeV, 5 % for 39 GeV, 0 % for 11.5 GeV appear to be necessary. This is consistent with decreasing Chiral Magnetic Effect as the incident energy decreases at RHIC. A reduced partonic interaction cross section is also needed for 11.5 GeV, indicating possible significant contributions from the hadronic stage. For Pb+Pb collisions at 2.76 TeV, 10% initial charge separation can produce similar behaviors as those at the top RHIC energy. We will also discuss how the same-charge correlation of <cos(1-2)> changes sign from negative at RHIC to positive at the LHC. Reference: [1] Guo-Liang Ma and Bin Zhang, Phys. Lett. B 700 (2011) 39–43, arXiv:1101.1701 [nucl-th]. Speaker: Guo-Liang Ma (Shanghai INstitute of Applied Physics (SINAP), CAS) • 4:00 PM Charge dependent azimuthal correlations of K-Pi pairs at STAR 2h Three-particle correlations have been used to probe for local parity violation (LPV) in the quark-gluon plasma (QGP) formed during Au+Au collisions at$\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) • 4:00 PM Charge dependent correlations relative to the fourth harmonic event plane and an estimate of the background effects in CME measurements 2h Charge 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)) • 4:00 PM Charm contribution to final hadron yield at LHC 2h Almost 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)) • 4:00 PM Charm production in the early phase and the charm baryon-to-meson ratios at LHC energies 2h The 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)) • 4:00 PM chi_c measurement in PHENIX: the present and the future. 2h Measurement 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) • 4:00 PM Chiral phase transition in a confining cold dense matter 2h The 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) • 4:00 PM Chiral phase transition in a dynamical linear sigma model. 2h One 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) • 4:00 PM Chiral symmetry breaking in QCD and related theories 2h For 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) • 4:00 PM Clustering of Color Sources and the Temperature Dependence of Shear Viscosity of the QGP in Central A-A Collisions at RHIC and LHC Energies 2h The 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) • 4:00 PM 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) • 4:00 PM Cold quark matter in astrophysics of compact stars 2h I 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) • 4:00 PM Collective flow in relativistic heavy ion collisions 2h Heavy-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) • 4:00 PM Collective Flow of Charged Hadrons in Cu+Cu collisions at$\sqrt{s_{NN}}$= 200 GeV at RHIC PHENIX 2h The collective flow of charged hadrons emitted in heavy ion collisions can be characterized using the Fourier coefficient$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$for charged hadrons, will be presented and compared to earlier measurements for Au+Au collisions at the same energy so as to see the effect of system size. Speaker: Damian Reynolds (S) • 4:00 PM Collision energy dependence of high transverse momentum$R_{CP}$of charged hadrons in STAR 2h The observed suppression of high transverse momentum ($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) • 4:00 PM Constraining properties of the deconfined state of matter with CHIMERA 2h Constraining 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) • 4:00 PM Constraining the Nuclear Equation of State by Neutron-Star Observables 2h Recently, 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) • 4:00 PM Construction of LMRPC modules for STAR-MTD 2h Data 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) • 4:00 PM Conventional effects in higher cumulant ratios of conserved charges in relativistic heavy ion collisions 2h Higher 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) • 4:00 PM Critical fluctuations of the higher moments of order parameter and energy from 3D-Ising, O(2) and O(4) models 2h Higher 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) • 4:00 PM Cross section, polarization and multiplicity dependence of J/psi production in pp collisions at the LHC 2h The 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)) • 4:00 PM D mesons$v_{2}$measurement with Q-cumulants and Scalar Product methods in Pb-Pb collisions at$\sqrt{s_{NN}}=2.76$TeV with the ALICE experiment 2h The ALICE experiment at the Large Hadron Collider (LHC) has been designed in order to characterize the quark gluon plasma (QGP) in high-energy heavy-ion collisions. D mesons are powerful probes of the medium since the charm quarks are produced at the early stage of the collision and experience its entire evolution. In particular, the anisotropy parameter$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$decay channels will be reported. Speaker: Grazia Luparello (NIKHEF (NL)) • 4:00 PM D*-hadron azimuthal correlations in pp collisions at$\sqrt{s} =7 TeV$with ALICE 2h Due to their relatively high mass, heavy-flavour quarks, produced in high-energy heavy-ion collisions, are sensitive probes of the interaction dynamics inside the hot and dense QCD matter. Since heavy quarks are produced in pairs during the initial stage of the collision, before the formation of the QGP, the measurement of heavy-flavour hadron production provides profound information on the properties of the produced medium. A detailed understanding of the pair production mechanisms in proton-proton collisions is interesting both as a QCD test tool as well as a reference for future heavy-ion studies. This particular physical process can be investigated using the angular azimuthal correlation between open-charmed mesons and charged hadrons. This correlation exhibits characteristic near-side and away-side structures that are produced by the charged hadrons from the fragmentation and decay of the partner charmed meson. The azimuthal direction is expected to be sensitive to the heavy quark production mechanism and can be compared to the perturbative QCD calculations. D mesons are reconstructed in several hadronic channels in the ALICE experiment at the LHC. Using$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)) • 4:00 PM Decomposition of flow and non flow in di-hardon correlations at RHIC 2h Angular 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) • 4:00 PM Density fluctuations at the QCD phase transition 2h We 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 • 4:00 PM Development of the Silicon Tracking System for the Compressed Baryonic Matter (CBM) Experiment at FAIR 2h The 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) • 4:00 PM Development of W+Si-pad/micro-pad based Electromagnetic Calorimeter for the ALICE upgrade 2h The 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 Speaker: Taku for the ALICE-FOCAL Collaboration Gunji (University of Tokyo (JP)) • 4:00 PM Di-electron Measurements in$p+p$collisions by PHENIX using the Hadron Blind Detector 2h Di-electrons are among the most promising probes for studying the early, hot and dense stages created in relativistic heavy-ion collisions. They are color neutral and so interact only electromagnetically, thus carrying to the detectors information about the conditions and properties of the medium at the time of their creation. The di-electrons are emitted over the the entire space-time evolution of the collision and their spectrum thus carries a wealth of information. PHENIX has measured a large, unexpected enhancement in$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$HBD analysis will be presented in this poster. Speaker: Deepali Sharma (S) • 4:00 PM Di-jet properties in pp at sqrt(s) = 7 TeV and Pb-Pb at sqrt(s_NN) = 2.76 by LHC-ALICE 2h A di-jet produced by a hard scattering of partons plays a vital role to characterize the properties of hot and dense QCD matter produced in Pb-Pb collisions at LHC. In particular, a di-jet is one of the key probes to look for a medium response due to a strong jet quenching effect, as reported by the CMS and ATLAS collaborations. In this analysis, we used the data collected by the ALICE collaboration, in pp collisions at sqrt(s) = 7 TeV and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. Charged and neutral leading jets have been used to study the momentum balance with the recoiling charged jet. The di-jet momentum balance (A_J) in pp at sqrt(s) = 7 TeV as a function of charged particle multiplicity has been measured and is compared with the PYTHIA simulation. We also report the status of an analysis of di-jet measurement in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV to search for a possible medium response by a propagation of high energy jet, which is sensitive to parton energy loss. Speaker: Tatsuya Chujo (University of Tsukuba (JP)) • 4:00 PM Dielectron Production in Au+Au-Collisions at$\sqrt{s_{NN}}$=39 \& 62.4 GeV at STAR 2h In the years 2010/11, the Solenoidal Tracker At RHIC (STAR) conducted a Beam Energy Scan (BES) over a wide range of center-of-mass energies with the purpose of studying the properties of the Quark-Gluon-Plasma (QGP) as well as searching for the onset of deconfinement and the critical point of the QCD phase diagram. The installation of the Barrel Time-Of-Flight-Detector (TOF) has enabled STAR to identify electrons over a wide momentum range. Combined with its large acceptance, excellent PID, and a low material budget in the runs of 2010/11, STAR now provides unique capabilities for the study of dielectron production in heavy ion collisions. Due to their negligible strong interaction with the dense medium created at RHIC, leptons can escape the interaction region undistorted and thus, carry direct information about the space-time evolution of the fireball created in relativistic heavy-ion collisions. In the special case of dileptons, their invariant mass ($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
Speaker: Mr Patrick Huck (CCNU/LBNL)
• 4:00 PM
Dijet asymmetry A_J within a partonic Boltzmann transport model 2h
Recent 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)
• 4:00 PM
Dimuon measurements in ALICE: The Muon Forward Tracker Upgrade Project 2h
The 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))
• 4:00 PM
Direct Photon - Hadron Pair Correlations Measurement in Au+Au Collision at PHENIX 2h
The 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)
• 4:00 PM
Direct Photon and Lepton Pair Production from Viscous quark-gluon plasma 2h
We 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 published
Speaker: Bikash Sinha (V)
• 4:00 PM
Direct photon capabilities of the proposed MPC-EX detector at PHENIX 2h
The 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)
• 4:00 PM
Direct Photon Measurements at PHENIX 2h
Direct 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
• 4:00 PM
Directed flow at midrapidity at the LHC 2h
We 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)
• 4:00 PM
Directed flow measurement in Pb-Pb collisions with ALICE at the LHC 2h
Directed 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))
• 4:00 PM
Dissipative Hydrodynamic Evolution of the QGP at Finite Baryon Density 2h
The 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)
• 4:00 PM
Dynamical freeze-out in event-by-event hydrodynamics 2h
In 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)
• 4:00 PM
Dynamical higher cumulant ratios of net and total protons at STAR 2h
Higher 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)
• 4:00 PM
Elastic scattering, total cross-section and charged particle pseudorapidity density in 7 TeV pp reactions measured by the TOTEM Experiment at the LHC 2h
The 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-2012-106
Speaker: Mate Csanad (for the TOTEM Collaboration)
• 4:00 PM
Elastic scattering: The undersides of quarkonia propagation and collectivity in the QGP 2h
One 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)
• 4:00 PM
Elliptic azimuthal anisotropy of neutral pions in PbPb collisions at 2.76 TeV with CMS 2h
The 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))
• 4:00 PM
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 2h
Heavy 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))
• 4:00 PM
Elliptic flow of strange and multi-strange hadrons in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV measured with ALICE 2h
Anisotropic 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)
• 4:00 PM
Energy dependence of fluctuations in p+p collisions at the CERN SPS 2h
NA61/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))
• 4:00 PM
Energy dependence of identified hadron multiplicity fluctuations in Heavy Ion collisions at the CERN SPS 2h
The 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)
• 4:00 PM
Enhanced Jet Quenching in Strongly Interacting Quark Gluon Plasma 2h
We 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)
• 4:00 PM
Entropy production in classical Yang-Mills system from color-glass condensate initial condition with noise 2h
Possible 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)
• 4:00 PM
Event anisotropy of electrons from charm and bottom quark decays in 200 GeV Au+Au collisions at RHIC-PHENIX 2h
The 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)
• 4:00 PM
Event by event di-hadron correlations in Pb-Pb 2.76 TeV collisions from the ALICE experiment 2h
The 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))
• 4:00 PM
Event-by-event distribution of azimuthal asymmetries in ultrarelativistic heavy-ion collisions 2h
Nowadays, 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)
• 4:00 PM
Event-by-Event Fluctuations in Initial Conditions in Relativistic Hydrodynamic Model 2h
To 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)
• 4:00 PM
Event-by-event generation of electromagnetic fields in heavy-ion collisions 2h
We 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)
• 4:00 PM
Event-by-event mean $p_{\rm T}$ fluctuations measured by the ALICE experiment at the LHC 2h
Results 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))
• 4:00 PM
Exclusive photoproduction of rho0 mesons in ultra-peripheral Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV 2h
The 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))
• 4:00 PM
Extruction of nontrivial correlation between chiral and deconfinement transitions from two-color QCD at imaginary chemical potential 2h
We 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)
• 4:00 PM
Flow correlations to constrain the properties of the initial conditions 2h
In 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)
• 4:00 PM
Fluctuating Hydrodynamics Confronts the Rapidity Dependence of Transverse Momentum Fluctuations 2h
Interest 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)
• 4:00 PM
FoCal - a high granularity electromagnetic calorimeter for forward direct photon measurements as an upgrade of ALICE 2h
We 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))
• 4:00 PM
Formation and decay of hadronic resonances in hot and dense nuclear matter 2h
One 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)
• 4:00 PM
Forward J/psi production in Au+Au and Cu+Au collisions at PHENIX 2h
One 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)
• 4:00 PM
Fourth order corrections to the MV model, multiplicity distributions and KNO scaling 2h
A 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)
• 4:00 PM
From dileptons to chiral symmetry restoration: Sum rules and the axial-vector spectral function. 2h
The 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)
• 4:00 PM
Fully dynamic simulations of heavy ion collisions in a pQCD-based partonic transport model 2h
We 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)
• 4:00 PM
Getteing primordial baryon number fluctuation from observed proton number fluctuation in relativistic heavy ion collisions 2h
We 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)
• 4:00 PM
Hadron-jet correlations measured in pp and Pb-Pb collisions in LHC-ALICE 2h
Heavy-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))
• 4:00 PM
The 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)
• 4:00 PM
Hadronic calorimetry R&D for future PHENIX 2h
Speaker: Dmitri Kotchetkov (Ohio University (US))
• 4:00 PM
Hadronic effects on the X(3872) meson abundance in heavy ion collisions 2h
We 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
• 4:00 PM
Hadronic Resonance States in an Effective Chiral Model 2h
With 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)
• 4:00 PM
Hadronization: does the chemical freeze-out curve meet the lattice QCD parton-hadron phase boundary ? 2h
We 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. C
Speakers: Francesco Becattini (Unversity of Florence) , Mr Tim Schuster (Yale University (US))
• 4:00 PM
Harmonious Harmonics? After the common origin of correlations and flow. 2h
We 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)
• 4:00 PM
HBT Measurements for charged pions in √s_{\text{}NN}=39, 62.4 and 200 GeV Au+Au collisions at RHIC-PHENIX 2h
HBT 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)
• 4:00 PM
HBT scaling results from UrQMD up to LHC energies 2h
We 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)
• 4:00 PM
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 2h
Heavy 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)
• 4:00 PM
Heavy quark energy loss in p+p collisions at the LHC 2h
One 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)
• 4:00 PM
Heavy quark production at forward rapidity in d+Au collisions at sqrt(s) = 200 GeV 2h
The 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)
• 4:00 PM
HEAVY QUARKONIA IN MEDIUM AS OPEN QUANTUM DISSIPATIVE SYSTEM, A WAVE FUNCTION BASED APPROACH 2h
In 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)
• 4:00 PM
Heavy-quark diffusion at the LHC within a UrQMD-hydrodynamical hybrid model 2h
Heavy 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)
• 4:00 PM
High-Energy Nuclear Collisions and the QCD Phase Structure 2h
One 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)
• 4:00 PM
High-pT direct photons in nuclear collisions: from RHIC to LHC 2h
We 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))
• 4:00 PM
High-pT neutral pion nuclear modification in PHENIX detector 2h
Neutral-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 Speaker: Norbert Novitzky (Helsinki Institute of Physics (FI)) • 4:00 PM Higher moments of Net Kaon multiplicity distributions at RHIC energies for the search of QCD Critical Point 2h The 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) • 4:00 PM Higher moments of net-charge multiplicity distributions at RHIC energies from STAR 2h To 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 calculations
Speaker: NIHAR R SAHOO (Variable Energy Cyclotron Centre)
• 4:00 PM
Hot quarkonium spectral functions from QCD sum rules and the maximum entropy method 2h
Quarkonia 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)
• 4:00 PM
How do Jets Affect the Collective Flow of the Quark-Gluon Plasma? 2h
In 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).
Jets 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.