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Int. Conference on the Initial Stages of High-Energy Nuclear Collisions
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Hotel Louxo - Illa da Toxa - Galicia (Spain)
Hotel Louxo - Illa da Toxa - Galicia (Spain)
Description
The meeting will be focused on the discussion of the present experimental and theoretical knowledge of the partonic structure of protons and nuclei; the corresponding conditions at the initial stages of the collision, including the role and nature of fluctuations; the subsequent hydrodynamical evolution; and the determination of viscosity or other medium properties. Providing a framework for cross-talk among different subfields is one of the main goals of the conference.
The conference will be held in September 8-14 2013 in Illa da Toxa (Galicia-Spain), a pleasant island joined to the mainland by a bridge. All sessions, lunches and lodging for registered participants will take place at hotel Louxo.
Participants
Adrian Dumitru
Alberica Toia
Aleksandra Romaszko
Alexander Milov
Alexis Moscoso Rial
Alina Czajka
Andrea Beraudo
Andrea Festanti
Andry Rakotozafindrabe
Anna Julia Zsigmond
Anne Sickles
Anthony Robert Timmins
Antonio Ortiz Velasquez
Axel Drees
Berndt Mueller
Berndt Mueller
Bjoern Schenke
Blaizot Jean-Paul
Brijesh Kumar Srivastava
Camelia Mironov
Carlos A. Salgado
Carlos Pajares Vales
Carlota Andrés
Carsten Greiner
Chin-Hao Chen
Constantinos Loizides
Cyrille Marquet
Daniel Pablos
Daniele De Gruttola
David Mateos
DIONYSIS TRIANTAFYLLOPOULOS
Dirk Rischke
Dmitri Kharzeev
Doga Can Gulhan
Eero Aleksi Kurkela
Ekaterina Retinskaya
Elena Gonzalez Ferreiro
Elena Petreska
Evgeny Shulga
Ferenc Sikler
Fernando Navarra
Francesco Barile
Frederique Grassi
Gabriel Denicol
Gay Ducati M.Beatriz
Gian Michele Innocenti
Giovanni Antonio Chirilli
Grigori Feofilov
Guilherme Teixeira De Almeida Milhano
Guillaume Beuf
Gunther Roland
Hannu Paukkunen
Hao Ma
Harri Niemi
Heikki Mäntysaari
Hideaki Iida
Hugo Denis Antonio Pereira Da Costa
Ian Brock
ismail zahed
Jan Rak
Javier Lopez Albacete
Jean-Philippe Lansberg
Jean-Yves Ollitrault
Jianwei Qiu
Jiri Kral
Johan Blouw
Jorge Casalderrey Solana
Julia Velkovska
Jurgen Schukraft
Kari J. Eskola
Katarzyna Deja
Koichi Murase
Konrad Tywoniuk
Larry McLerran
Laurent Aphecetche
Li Yi
Liliana Apolinario
Lukasz Kamil Graczykowski
Malgorzata Anna Janik
Manoel Anxo Rodríguez-Moldes Díaz
Manoel Rodriguez Calvo
Marcus A. Torres
Maria Zurita
Marina Nielsen
Mark Strikman
Masaru Hongo
Mateusz Ploskon
Matthew Luzum
Mauricio Martinez Guerrero
Michael Strickland
Michal P. Heller
mikhail braun
Nan Su
Nestor Armesto Perez
Paul Kuijer
Peter Christiansen
Piotr Bozek
Radoslaw Ryblewski
Raju Venugopalan Venugopalan
Rik Yoshida
Risto Paatelainen
Rudy Marty
Sanghoon Lim
Sarah La Pointe
Sergei Voloshin
Shengquan Tuo
Shingo Sakai
Shoichiro Tsutsui
Souvik Priyam Adhya
Stanislaw Mrowczynski
Stefan Floerchinger
Stephen Sanders
Tetsufumi Hirano
Thomas Epelbaum
Tolga Altinoluk
Urs Wiedemann
Vadim Guzey
Vincenzo Greco
Vinod Chandra
Volodymyr Konchakovski
Volodymyr Magas
Wilke van der Schee
Wojciech Florkowski
Xabier García Feal
Yan Zhu
Yaxian Mao
Yogesh Kumar
Yuji Hirono
Support
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Reception of the participants
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10:30
Coffee Break
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Thermalization (I)
- 4
- 5
- 6
- 7
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13:00
Lunch break
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Collectivity in small systems: pp and pA (I)
- 8
- 9
- 10
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16:00
Coffee break
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Collectivity in small systems: pp and pA (II)
- 11
- 12
- 13
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Partons in high energy hadronic and nuclear collisions (I)
- 14
- 15
- 16
- 17
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11:00
Coffee break
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Partons in high energy hadronic and nuclear collisions (II)
- 18
- 19
- 20
- 21
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13:30
Lunch break
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Partons in high energy hadronic and nuclear collisions (III)
- 22
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23
Coherence effects between the initial and final state radiation in a dense QCD mediumIn this work we investigate medium modifications to the interference pattern between initial and final state radiation. We compute single gluon production off a highly energetic parton that undergoes a hard scattering and subsequently crosses a dense QCD medium of finite size. We extend our previous studies obtained at first order in opacity by providing general results for multiple soft scatterings and their specific formulation within the harmonic oscillator approximation. We study the interplay of the two relevant scales of the problem: the medium length L and the decorrelation time of the gluon due to the medium $\tau_f$. This interplay gives origin to two different asymptotic limits of the gluon spectrum: the coherent ($\tau_f\gg L^+$) and incoherent regime ($\tau_f\ll L^+$). We discuss the main characteristics of each regime. We comment on possible phenomenological consequences of this setup in high-energy nuclear collisions.Speaker: Mauricio Martinez Guerrero (Universidade de Santiago de Compostela)
- 24
- 25
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17:00
Coffee break
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Discussion session on centrality in pPbConvener: Jorge Casalderrey Solana (University of Barcelona (ES))
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26
ALICE Measurements in p-Pb collisions: Multiplicity, Centrality and Implications for Binary ScalingMeasurements of particle production in proton-nucleus collisions provide a reference to disentangle final state effects, i.e. signatures of the formation of a deconfined hot medium, from initial state effects, already present in cold nuclear matter. Since many initial state effects are expected to vary as a function of the number of collisions suffered by the incoming projectile, it is crucial to estimate event-by-event the centrality of the collision. In p-Pb collisions, the low particle multiplicities and the large multiplicity fluctuations influence the way collisions are categorized into different centrality classes using a particle multiplicity distribution. We present ALICE measurements of particle production in p-Pb collisions at sqrt(s_NN)=5.02 TeV, including the pseudo-rapidity and transverse momentum dependence, we discuss the event classification in centrality classes and its implications for the measurements of nuclear modification factors.Speaker: Dr Alberica Toia (Universita e INFN (IT))
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27
Centrality determination in pPb collisions with CMSCentrality is very important for defining the collision system size in heavy ion collisions. It provides a tool for selecting events in a similar way in different experiments and facilitates the comparison of experimental results and theoretical calculations. The progress of centrality determination in pPb collisions at CMS is presented. The choice of variables used for event classification will be discussed. The method for the estimation of geometric quantities, such as the number of nucleon participants, nucleon-nucleon collisions, and impact parameter will be shown.Speaker: Mr Shengquan Tuo (Vanderbilt University)
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26
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Global and collective dynamics (I)
- 28
- 29
- 30
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10:30
Coffee break
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Global and collective dynamics (II)
- 31
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- 33
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34
Mode-by-mode hydrodynamicsThe heavy ion experimental programs at the LHC and RHIC provide evidence that relativistic hydrodynamics can well describe many of the dynamical properties of the hot and dense medium produced there. Moreover, event-by-event fluctuations in the initial configuration play an important role, in particular they determine to a large extent the correlations of particles in azimuthal angle and rapidity. We propose here a new, more differential characterization of fluctuations in the hydrodynamical initial state and discuss the influence of these fluctuations on experimental observables such as particle spectra and harmonic flow coefficients.Speaker: Stefan Floerchinger (Deutsche Forschungsgemeinschaft (DE))
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13:00
Lunch break
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14:30
Free afternoon
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20:00
Walk and tapas in San Vicente
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Thermalization (II)
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Isotropization of the GlasmaIn recent years, the problem of thermalization in Heavy Ion Collision has received much attention, but has yet to be solved. The issue is that on the one hand, viscous hydrodynamics simulations suggest that the matter produced in such collisions (called the Quark Gluon Plasma, or QGP) behaves like a nearly perfect fluid, and does so very shortly after the collision (around 1 fm/c). Since hydrodynamics requires local thermal equilibrium, this tends to show that the QGP has thermalized during the very early stages of the collision. On the other hand, theoretical models (based on microscopic theories like the Color Glass Condensate, or CGC) predict that the QGP is very far from local thermal equilibrium at the initial time (its energy-momentum is very anisotropic). One of the approaches developed to study this non-perturbative problem in QCD is a resummation scheme that amounts to averaging over classical fields, with random initial conditions. Its numerical implementation is presented here for the case of a scalar field theory with quartic coupling, that shares some important features with QCD. In particular, we will show the relevance of this resummation in capturing the physics relevant for thermalization. Analytical and numerical results concerning the case of QCD will also be presented.Speaker: Mr Thomas Epelbaum (IPhT)
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11:00
Coffee break
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Global and collective dynamics (III)
- 39
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- 41
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13:00
Lunch break
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Parallel talks - Session 1A
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42
Stabilizing Perturbative Yang-Mills Free Energy with Gribov QuantizationWe evaluate the free energy of the Yang-Mills theory using the Gribov quantization that copes with non-perturbative resummation. The magnetic scale is automatically incorporated in the framework and we find it efficient to stabilize the perturbative expansion of the free energy. In the range of the temperature T=Tc~2Tc major uncertainty in our results comes from the non-perturbative running coupling that is adopted from the lattice simulation, while the convergence above 2Tc is impressively robust.Speaker: Dr Nan Su (Bielefeld University)
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Numerical Simulation of Anomalous HydrodynamicsAnomaly induced transport effects, like the Chiral Magnetic Effect or the Chiral Separation Effect, have recently attracted much attention and are expected to be observed in ultra-relativistic heavy-ion collisions. So far, the evidence in the experiments has been elusive, mainly due to the lack of quantitative theoretical predictions. In order to asses the contributions from anomalous transport in heavy-ion collisions, we consider a hydrodynamic model in the presence of anomaly. We numerically solve the anomalous hydrodynamic equations under a background electromagnetic field and calculate the propagation of the chiral magnetic wave in an expanding quark-gluon plasma. The charge-dependent elliptic flow ($v_2^\pm$) is recently proposed as a signal of the chiral magnetic effect. We calculate the charge-dependent particle distributions and estimate the contribution from anomaly to $v_2^\pm$.Speaker: Masaru Hongo (The University of Tokyo)
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The influence of initial conditions on the final observables for heavy-ion collisions at RHIC energiesEvery dynamical description of heavy-ion collisions --whether based on hydrodynamics or on a parton cascade-- starts out with the modeling of the 'initial condition', i.e. the state of the system after the first initial energetic collisions between target and projectile nucleons. Usually it is assumed that the whole system or at least the quark-gluon plasma comes to a thermal equilibrium after 1fm/c and then hydrodynamics can be employed. We present a systematic study of the influence of the initial conditions on the final observables for heavy-ion reactions by investigating this reaction for different intial conditions with the novel molecular dynamics (MD) transport approach based on the the Nambu-Jona-Lasinio (NJL) model. The NJL Lagrangian whose parameters are adjusted to properties of free mesons and their decay constants allows for a description of the expansion of a quark-antiquark plasma whose constituents interact by potential and collisional interactions. It describes as well the transition of the plasma to the hadronic world. For our comparison we use a 'smooth' initial conditions of the Glauber type as well as the 'lumpy' energy density profile from the microscopic PHSD (Parton-Hadron-String-Dynamics) transport approach which incorporates the hadronic and partonic interactions. For these different initial conditions we present the results for the transverse differential spectra dN/dpt and the elliptic flow v2 for Au+Au at RHIC energies. We analyse furthermore the origin of these differences and whether the experimental spectra allow for a conclusion about the structure of the initial conditions.Speaker: Rudy Marty (FIAS (Frankfurt, GERMANY))
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45
Multi-parton interactions, color reconnection and collective dynamicsMulti-parton interactions (MPI) is a key ingredient in the successful phenomenological description of hadron-hadron collisions. In the hadronization of MPI, final partons originating from different partonic sub-collisions can interact with each other through color strings: the so-called color reconnection (CR) mechanism. In this work we show that CR produces a radial flow-like effect giving rise to mass ordering. The study is done within the framework of Pythia 8. We present results for different observables with identified hadrons in minimum bias pp collisions at sqrt(s)= 7 TeV. We show that the flow-like effect increases in events with large MPI activity and therefore with increasing multiplicity. We discuss how CR generates radial and possibly elliptic flow and what the role of this mechanism could be in other systems like p-Pb.Speaker: Antonio Ortiz Velasquez (Lund University (SE))
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46
Fluctuations in an integrated dynamical approach for heavy-ion collisionsRecently, the higher harmonics v_n (n>2) are systematically observed at RHIC and LHC and attract a lot of theoretical and experimental interests. Initial state fluctuations turned out to be important to explain these higher harmonics through event-by-event hydrodynamic simulations. In addition attempts are made to extract transport properties of the created matter such as shear viscosity from the higher harmonics data. In the heavy-ion reactions, the higher harmonics are created not only by initial state fluctuations. For example, thermal fluctuation in the hydrodynamic stage of the quark-gluon plasma also plays an important role in event-by-event descriptions. To obtain the properties of the quark-gluon plasma from experimental data quantitatively, an integrated dynamical approach which describe all the stages of the heavy-ion reaction is required. The approach includes models of initial states, hydrodynamics of quark-gluon plasma and subsequent hadronic cascades. It is important to properly implement all the possible sources of fluctuations in an integrated model and perform event-by-event simulations for quantitative analysis. First, we formulate the relativistic fluctuating hydrodynamics with the thermal fluctuaion by putting an emphasis on non-linearity and causality, and discuss significant behavior of the fluctuations using the fluctuation-dissipation relations. Also, recent results obtained by massive number of event-by-event simulations are shown.Speaker: Koichi Murase (The University of Tokyo)
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Elliptic Flow from Non-equilibrium Initial Conditions with a Saturation ScaleA current goal of relativistic heavy ion collisions experiments is the search for a Color Glass Condensate (CGC) as the limiting state of QCD matter at very high density. In viscous hydrodynamics simulations, a standard Glauber initial condition leads to estimate $4\pi \eta/s \sim 1$, while employing the Kharzeev-Levin-Nardi (KLN) modeling of the glasma leads to at least a factor of 2 larger $\eta/s$. Within a kinetic theory approach based on a relativistic Boltzmann-like transport simulation, our main result is that the out-of-equilibrium initial distribution reduces the efficiency in building-up the elliptic flow. At RHIC energy we find the available data on $v_2$ are in agreement with a $4\pi \eta/s \sim 1$ also for KLN initial conditions. More generally, our study shows that the initial non-equilibrium in p-space can have a significant impact on the build-up of anisotropic flow.Speaker: Vincenzo Greco (University of Catania)
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42
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Parallel talks - Session 1B
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48
Color Class Condensate from electron-proton DIS to proton-nucleus collisionsThe Color Class Condensate offers a consistent framework to describe high-energy (small-x) data from various experiments. The non-perturbative input for these calculations, the dipole-target amplitude at initial Bjorken-x, is obtainable from electron-proton deep inelastic scattering processes. Once that is known, one can compute, for example, single and double inclusive particle production in proton-proton and proton-nucleus collisions. Proton-nucleus collisions are especially interesting as the saturation scale is expected to scale as A^1/3, making saturation phenomena easier to observe in pA than pp collisions. We discuss how tightly the electron-proton DIS data constrains the initial condition for the dipole amplitude and how the LHC single inclusive spectra can be used to further test the CGC picture. Then using only information from DIS experiments we generalize the dipole amplitude to nuclear targets and compute particle production in proton-nucleus collisions [1]. We present predictions for the nuclear suppression factor R_pA at forward rapidities and compare with pQCD calculations. We also discuss how the back-to-back structure of the forward dihadron production cross section is modified when moving from proton-proton to proton(deuteron)-nucleus collisions, as naturally understood in the CGC [2]. References: [1] T. Lappi, H. Mäntysaari, in progress [2] T. Lappi, H. Mäntysaari, Nucl. Phys. A908 (2013) 51-72Speaker: Heikki Mäntysaari (University of Jyväskylä)
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49
JIMWLK evolution for multi-particle production in Langevin formWe study multi-particle production with rapidity correlations in proton-nucleus collisions at high energy in the Color Glass Condensate framework. The high-energy evolution responsible for such correlations is governed by a generalization of the JIMWLK equation describing the simultaneous evolution of the strong nuclear color fields in the direct amplitude and the complex conjugate amplitude. This functional equation can be used to derive ordinary evolution equations for the cross-sections for particle production but the ensuing equations appear to be too complicated to be useful in practice, even at large Nc. We propose an alternative formulation based on a Langevin process, which is better suited for numerical implementations, and we present the stochastic equations appropriate for two gluon production.Speaker: DIONYSIS TRIANTAFYLLOPOULOS (ECT*)
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50
From full stopping to transparency in a holographic model of heavy ion collisionsNumerically simulating colliding planar gravitational shock waves in AdS gives rise to rich and interesting dynamics. Wide shocks come to a full stop and expand hydrodynamically, as was found in [1]. High energy collisions (corresponding to thin shocks) pass through each other, after which a plasma forms in the middle, quite akin to heavy-ion collisions. After an initial stage of far-from-equilibrium evolution the pressures become positive and are governed by hydrodynamics within a proper time 1/T, with T the local temperature at that time. In the end I will comment on recent results where we were able to perform a somewhat similar simulation for central collisions and matched this with recent hydrodynamic and hadronic cascade codes, which enables an interesting comparison with transverse spectra for light particles. [1] P.M. Chesler, L.G. Yaffe, (PRL 2011) [2] J. Casalderrey-Solana, M.P. Heller, D. Mateos, W. van der Schee, 1305.4919 [3] W. van der Schee, P. Romatschke, S. Pratt (to appear)Speaker: Wilke van der Schee (U)
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51
Solution of the NLO BFKL Eq. and analytic NLO $\gamma^*$-$\gamma^*$-cross section from High-Energy OPE in Wilson-linesI will present the solution of the next-to-leading order (NLO) BFKL equation obtained by constructing its eigenfunctions perturbatively, using an expansion around the LO BFKL (conformal) eigenfunctions. This method can be used to construct the solution of the BFKL equation with the kernel calculated to an arbitrary order in the coupling constant. Then, using the solution of the NLO BFKL equation and the NLO pomeron impact factor recently calculated by using the high-energy Operator Product Expansion (OPE) in Wilson lines, I will construct the analytic NLO cross section of $\gamma^*$-$\gamma^*$-scattering process at high-energy.Speaker: Giovanni Antonio Chirilli (The Ohio State University)
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52
Thermalization and entropy production from Glasma-like initial condition in classical Yang-Mills dynamicsThermalization process in classical Yang-Mills (CYM) field theory starting from noisy Glasma-like initial conditions is studied by investigating the initial-value sensitivity of trajectories [1]. The Kolmogorov-Sinai (KS) entropy, which gives the entropy production rate in classical chaotic system, is calculated numerically for CYM fields starting from Glasma-like initial conditions with and without fluctuations. For small random fluctuations we observe initial-value sensitivity of the system, while no sensitivity is observed without fluctuations. We analyze the intermediate time Lyapunov spectrum for several time windows and calculate KS entropy defined by the sum of positive Lyapunov exponents. We find a large number of positive Lyapunov exponents at the early stages of time evolution. Also for later times their number is a sizeable fraction of the total number of degrees of freedom. Thus we conclude that for glasma-like initial conditions a significant amount of entropy is produced by classical gluon field dynamics. Reference: [1] H.Iida, T.Kunihiro, B.Muller, A.Ohnishi, A.Schafer and T.T.Takahashi, arXiv:1304.1807 (2013), to appear in Phys. Rev. D.Speaker: Dr Hideaki Iida (Kyoto University)
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53
Inclusive hadron and photon production at LHC in dipole momentum spaceUsing a momentum space model for the dipole scattering ampli tude we present an analysis of the saturation effects at LHC energies, describing the data on proton-proton and proton-lead collisions.The model is based on the asymptotic solutions of the Balitsky-Kovchegov equation, being ideal in the saturation domain where the target wave function has a high occupation number. We also make predictions for the nuclear modification ratios on charged hadron and prompt photon production in the forward region, where the high parton density effects are important.Speaker: Prof. Maria Beatriz Gay Ducati (UFRGS)
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48
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16:30
Coffee break
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Parallel talks - Session 2A
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54
Light-flavour hadron production in p-Pb collisions measured with the ALICE detector at the LHCThe LHC has recently provided p-Pb collisions at √sNN = 5.02 TeV which play a fundamental role in the understanding of cold nuclear matter effects in heavy ion collisions, providing essential information to discriminate between initial and final state effects. Results from two-particle correlation measurements have revealed an unexpected double ridge structure in these collisions, which could be interpreted either as a sign of collective flow or as an initial state effect related to saturation phenomena. In this talk we present results on identified particles as a function of multiplicity, to investigate possible indications of radial flow. Charged and weakly decaying neutral particles are reconstructed in the ALICE central barrel over a wide momentum range and identified by employing different sub-systems and techniques. Transverse momentum spectra of primary charged particles and identified light flavoured hadrons have been measured. The yields, average pT, and particle ratios are reported as a function of multiplicity, and compared to other collision systems and theoretical models.Speaker: Francesco Barile (Universita e INFN (IT))
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55
Identical pion interferometry in ALICE at the LHCWe report on the results of a femtoscopic analysis with identical pions measured by ALICE in the collisions of protons and lead ions. The technique of femtoscopy, based on intensity interferometry (also known as Hanbury-Brown Twiss interferometry, or HBT) allows one to relate a pair momentum difference to the space-time characteristics of the sources created in particle collisions. The femtoscopic analysis is performed using both the spherical harmonics decomposition and the 3D Cartesian representation. HBT radii, which reflect the size the source, are obtained by fitting the resulting correlation function. We present the dependence of these radii on the pair transverse momentum and the multiplicity of the event and describe the observed scalings.Speaker: Malgorzata Anna Janik (Warsaw University of Technology (PL))
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56
Studying the medium behavior of the dilute system in d+Au collisions via two particle Correlations in PHENIXThe collective flow in the quark gluon plasma has been studied in detail and provides important insights into this QCD medium. However, there is little known about the flow in dilute systems, such as d+Au collisions at RHIC. In high multiplicity 7 TeV p+p collisions and 5.02TeV p+Pb collisions at the LHC, a v2 like structure and long range correlations have been observed. To study the possible flow behavior in d+Au collisions at lower energy, various two particle correlations are measured in PHENIX. When both trigger and partner particles are measured at mid-rapidity, $|\eta|<0.35$, after removing the jet contribution, $v_2$ is extracted from the excess in most central d+Au collision. The result is compared with theoretical calculations. When a trigger particle is correlated with an associated particle at forward/backward rapidity ($3.1<|\eta|<3.9$), a "ridge" like structure has been found in the near-side in the Au-going direction, but is absent in the d-going side. These studies may improve our understanding of the behavior of the medium in small systems.Speaker: Dr Chin-Hao Chen (RIKEN BNL Research Center)
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Long-range correlations in pp and A-A collisions from ALICEThe first experimental results on forward-backward (FB) multiplicity correlations in proton-proton collisions have shown considerable long-range effects. These are seen at all three LHC energies ( 0.9, 2.76 and 7 TeV) and will provide useful input in studying long range correlations in A-A collisions. It is shown that the FB multiplicity correlation measurements, done in ALICE for various configurations of azimuthal sectors, enable separation of the short - and long - range effects. This allows us to determine that the long-range component provides the dominant contribution to the correlation strength in the given case of pp collisions. Results are discussed and compared to PYTHIA and PHOJET MC event generators and to a model based on the string picture of hadronic interactions. All three models indicate that the observed behavior of the correlation strength in azimuth and rapidity is compatible with multi-particle production by independent string emitters. The long-range part arises due to event-by-event fluctuations of the number of emitters while the short-range part is due to pair correlations between particles produced by the same emitter. Theoretical motivations for further search and studies of these correlations in A-A and pp collisions are also discussed briefly including two models: the String Fusion Model (SFM) and the Color Glass Condensate (CGC).Speaker: Grigori Feofilov (St. Petersburg State University (RU))
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58
Angular correlations measured in pp collisions at the LHC by the ALICE experimentDeltaEta-DeltaPhi distributions (the difference of two particle pseudorapidity and azimuthal angle) allow us to study the wide landscape of correlations and are expected to exhibit several structures which arise from different physics mechanisms. They are sensitive to a number of correlations i.e. minijets, elliptic flow, Bose-Einstein correlations, resonance decays, momentum and other conservation laws, etc. The observed features in the final shape of the system arise from the complex interplay of these processes. We attempt to quantify them in this analysis. The results will be compared to theoretical models, to verify their predictions and provide input for their improvement in describing new experimental results. The studies of two-particle angular correlations measured in proton-proton collisions at a center of mass energy 7 TeV registered by ALICE at the LHC will be reported, including the dependence of the correlation function on the multiplicity of the event and on the charge combination of particles in the pair.Speaker: Lukasz Kamil Graczykowski (Warsaw University of Technology (PL))
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On the onset of the ridge structure in the framework of string percolationThe RHIC data on Au-Au collisions at 62.4 and 200 GeV/c show that the strength and width of the ridge structure for near side particles change sharply at different number of charged particle multiplicities. The LHC data on pp and p-Pb show that there is also a change on the strength of the ridge structure above certain number of charged particle multiplicity. We describe an unified picture for every kind of collisions of this onset of the ridge structure in the framework of string percolation. This picture is able to describe the observed different rise of the mean transverse momentum as a function of the multiplicity for pp at 0.9, 2.76 and 7 TeV, p-Pb at 5.02 TeV and Pb-Pb at 2.76 TeV.Speaker: Mr Alexis Moscoso (Universidade de Santiago de Compostela)
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54
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Parallel talks - Session 2B
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60
Analysis of p-Pb data via reweightingNew data form the LHC proton-lead run shall be available soon. Wether it is compatible with previous nuclear data or not should be done by its inclusion in a time consuming full global fit of initial state nuclear effects. One possibility to avoid such a procedure is to employ the reweighting technique, already used by the NNPDF collaboration. In this work we apply the reweighting to the study Drell-Yan and single inclusive hadroproduction pseudodata, and discuss its compatibility with a current sets of nuclear parton distributions.Speaker: Maria Zurita (Buenos Aires University)
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61
J/psi production in p-Pb collisions with ALICE at the LHCALICE, the dedicated heavy-ion detector at the LHC, observed J/psi suppression in Pb-Pb collisions at sqrt(s_NN)=2.76 TeV. The interpretation of that observation can be helped by performing a similar measurement in p-Pb collisions, where only cold nuclear matter effects are relevant. In this talk we will show results on inclusive J/psi production in p-Pb collisions at sqrt(s_NN)=5.02 TeV in the rapidity domains 2.03 < y_cms < 3.53 and -4.46 < y_cms < -2.96. The J/psi measurement is performed in the Muon Spectrometer through the mu+mu- decay mode, down to zero transverse momentum. Cross-sections and nuclear modification factors, integrated as well as differentially in y and pT, will be presented and will be compared to available theory calculations.Speaker: Laurent Aphecetche (Subatech)
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62
Nuclear Matter effects on Quarkonia and Heavy-QuarksThe recent pPb run at 5 TeV which took place at CERN LHC provides exciting measurements of the Nuclear Matter (NM) effects, especially for the heavy quark and quarkonium sectors. The comparison of the experimental results to the phenomenological inputs at this unprecedented energy is eagerly expected. We study the NM effects on J/psi [1], Upsilon [2] and open beauty [3] production. We consider an exact 2 to 2 kinematics (as expected from LO pQCD) for the bulk of the heavy-quark and quarkonium [4] production process. We show that the evaluation of the J/psi nuclear modification factor R_pPb suffers from large factorisation scale uncertainties, on top of the already large uncertainties due to the current knowledge of the nuclear modifications (shadowing, EMC effects, ...) of the parton distribution. Such scale uncertainties are reduced for the Upsilon case, owing to the larger mass and hence the larger scale of the production process. Also, we advocate that the nuclear absorption of the pre-resonant b\bar{b} pair should be negligible at LHC energies. We finally emphasize the complementarity between the studies of open heavy flavour and quarkonium production in pA collisions. Indeed, there is no debate that the heavy quark propagates as a colored object in the nuclear matter. On the contrary, for the quarkonia, there is neither a consensus on the impact of the possible break-up of the heavy quark pair in the matter nor on whether the pair propagates in a color singlet or octet state and is thus subject to a fractional energy loss, recently revived in the literature [5]. References [1] E. G. Ferreiro, F. Fleuret, J. P. Lansberg and A. Rakotozafindrabe, arXiv:1305.4569 [hep-ph]. [2] E. G. Ferreiro, F. Fleuret, J. P. Lansberg, N. Matagne and A. Rakotozafindrabe, Eur. Phys. J. C 73 2427. [3] E. G. Ferreiro, J. P. Lansberg, F. Fleuret, A. Rakotozafindrabe, in preparation. [4] E. G. Ferreiro, F. Fleuret, J. P. Lansberg and A. Rakotozafindrabe, Phys. Lett. B 680 (2009) 50. [5] F. Arleo, S. Peigne, T. Sami, Phys. Rev. D83 (2011) 114036.Speaker: Andry Rakotozafindrabe (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))
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D-meson production at central rapidity in pp and Pb-Pb collisions at the LHC with the ALICE detectorIn hadron collisions at the LHC, charm quarks are produced almost exclusively in initial hard parton scattering processes because of their large mass. Therefore, charm hadrons are excellent probes to study the dynamics of the hot and dense Quark-Gluon Plasma (QGP) produced in such collisions. For the quantitative interpretation of measurements in heavy-ion collisions it is mandatory to establish a baseline in proton-proton (pp) collisions where the elementary charm production mechanism can be investigated. In a recent measurement with ALICE, the J/Psi yield in pp collisions at c.m. energy of 7 TeV was observed to increase with increasing charged particle multiplicity, which might indicate that multiparton interactions are also relevant for heavy-flavour production. To further substantiate this finding it is crucial to investigate the multiplicity dependence of the total charm yield in pp collisions, e.g. via the measurement of D mesons. We present the current results on the charged particle multiplicity dependence of D0, D+, and D*+ meson yields in pp collisions at 7 TeV c.m. energy. The D mesons were reconstructed exclusively with ALICE in their hadronic decay channels at mid-rapidity in various transverse momentum intervals. The results will be discussed in the context of the previous measurements of J/Psi yields.Speaker: Gian Michele Innocenti (Universita e INFN (IT))
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Leptons from heavy flavour decays in pp, p-Pb, and Pb-Pb collisions with ALICEAt LHC energies heavy-ion collisions produce a high energy density QCD matter. One important probe of this matter are heavy-flavour quarks, as they are primarily produced in the early stage of the collision through initial hard scatterings, thus experiencing the full evolution of the system. In ALICE heavy-flavour production is studied in pp, p-Pb, and Pb-Pb collisions through the measurement of open heavy-flavour hadrons and single leptons from heavy-flavour hadron decays. These final state measurements provide insight into the charm and beauty quark interaction with the hot and dense medium, which can be acquired by measuring correlations of heavy-flavour hadrons (or their decay products) with other particles produced in the collision. For example, properties of the deconfined medium can be studied through the measurement of the elliptic flow (v2), which represents the second Fourier coefficient of the particle azimuthal distribution relative to the reaction plane. In other words, v2 is a correlation of the particle of interest in the transverse plane with all other particles produced in the collision. At low transverse momentum v2 probes the level of thermalization of heavy-flavour quarks, while at high transverse momentum offers information on in-medium, path length dependent, quark energy loss. Another relevant measurement is the azimuthal correlation of heavy-flavour decay electrons and charged hadrons, which can be utilized to estimate the relative contribution of charm and beauty hadrons to the measured heavy-flavour single electron yield in pp collisions, while also providing a tool to examine the the production and fragmentation of heavy quarks in other systems. In this contribution we focus on the measurement of leptons from semi-leptonic decays of heavy-flavour hadrons. We present the elliptic flow measurement of heavy-flavour decay electrons and muons as a function of transverse momentum at mid-rapidity and forward rapidity, respectively, for semi-central (20-40%) Pb-Pb collision at sqrt(s_NN)=2.76 TeV. In addition, we present the relative contributions from beauty and charm hadron decays to the total heavy-flavour electron yield in pp collisions at mid-rapidity as a function of transverse momentum, along with the resulting correlation functions in p-Pb collisions at sqrt(s) = 5.02 TeV and Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV. Comparison to results obtained at lower collision energy at RHIC and various theoretical models will also be shown.Speaker: Sarah La Pointe (University of Utrecht (NL))
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Precision proton-nucleus collision studies at A Fixed-Target ExpeRiment at the LHC (AFTER@LHC)We outline the physics opportunities [1] which are offered by a next generation and multi-purpose fixed-target experiment exploiting the LHC beams extracted by a bent crystal. This mature extraction technique offers an ideal way to obtain a clean and very collimated high-energy beam, without altering at all the performance of the LHC [2,3,4]. The multi-TeV LHC beams grant the most energetic fixed-target experiment ever performed, to study pp, pd and pA collisions at sqrt(s_NN) ~ 115 GeV and PbA collisions at sqrt(s_NN) ~ 72 GeV. AFTER -- for A Fixed-Target ExperRiment -- gives access to new domains of particle and nuclear physics complementing that of collider experiments, in particular RHIC and the projects of electron-ion colliders. The typical instantaneous luminosity achievable with AFTER in pp and pA mode [1] surpasses that of RHIC by more than 3 orders of magnitude and is comparable to that of the LHC collider mode, without pile-up thanks to the slow extraction mode. This provides a quarkonium and heavy-flavour observatory [5] in pp and pA collisions where, by instrumenting the target-rapidity region, gluon and heavy-quark distributions of the proton, the neutron and the nuclei can be accessed at large x and even at x larger than unity in the nuclear case. The nuclear target-species versatility provides a unique opportunity to study the nuclear matter versus the hot and dense matter formed in heavy-ion collisions, including the formation of the quark-gluon plasma. Modern detection technology should allow for the study of quarkonium excited states, in particular the chi(c) and chi(b) resonances, even in the challenging high-multiplicity environment of pA and PbA collisions, thanks to the boost of the fixed-target mode. Precise data from pp, pA should help to better understand heavy-quark and quarkonium production as well as their correlations with isolated photons, to clear the way to use them for gluon and heavy-quark PDF extraction in free and bound nucleons, to unravel cold from hot nuclear effects and to restore the status of heavy quarkonia as a golden probe of the QGP formation. The fixed-target mode also has the advantage to allow for spin measurements with polarized targets. [1] S. J. Brodsky, F. Fleuret, C. Hadjidakis and J. P. Lansberg, Phys. Rept. 108 522 (2013) 239. [2] E. Uggerhøj, U. I. Uggerhøj, Nucl. Instrum. Meth. B 234 (2005) 31. [3] W. Scandale, et al., Phys. Lett. B 703 (2011) 547-551. [4] W. Scandale, et al. [LUA9], CERN-LHCC-2011-007, 2011. [5] J. P. Lansberg, S. J. Brodsky, F. Fleuret and C. Hadjidakis, Few Body Syst. 53 (2012) 11-25Speaker: Jean-Philippe Lansberg (IPN Orsay, Paris Sud U. / IN2P3-CNRS)
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21:00
Conference dinner
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Small-x physics and the parton structure
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10:30
Coffee break
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Global and collective dynamics (IV)
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Constraining models of initial state with v2 and v3 data from LHC and RHICWe present a combined analysis of elliptic and triangular flow data from LHC and RHIC using viscous relativistic hydrodynamics. Elliptic flow v2 in hydrodynamics is proportional to the participant eccentricity eps2 and triangular flow is proportional to the participant triangularity eps3, which means vn_exp=(v_n/eps_n)_hydro*eps_n, n=2,3. Experimental data for v2 and v3 combined with hydro calculations of v_n/eps_n thus provide us with the initial anisotropies eps2 and eps3. By varying free parameters in the hydro calculation (in particular the shear viscosity), we obtain an allowed band in the (eps2, eps3) plane. Comparison with Monte-Carlo models of the initial state allows us to exclude several of these models.Speaker: Ekaterina Retinskaya (CEA)
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Multiplicities, p_T spectra and v_2 in A+A collisions at LHC and RHIC from NLO-improved pQCD + saturation + hydrodynamics modelWe report the results from the recent studies [1,2], where we have brought the EKRT framework [3] to next-to-leading order (NLO) in pQCD, and shown the viability of the model in describing the produced initial QGP energy densities at the LHC and RHIC. Our updated framework [1] combines a rigorous NLO pQCD computation of the minijet transverse energy production with the saturation of gluons and fluid dynamics. Latest knowledge of NLO nuclear parton distributions (nPDFs) is utilized. Identifying the key parameters and charting the uncertainties of the model, we obtain an encouragingly good agreement with the charged-particle multiplicities and identified bulk hadron p_T spectra measured in 5% most central Au+Au collisions at RHIC and Pb+Pb at the LHC [1]. To obtain the initial QGP energy-density profiles dynamically in non-central collisions [2], we supplement the calculation by a local saturation condition and impact-parameter dependent nPDFs (EPS09s [4]). We address the main uncertainties associated with the obtained initial states. Using viscous fluid dynamics, we show that a good simultaneous description of the centrality dependence of multiplicity, p_T spectra and elliptic flow is obtained both at the LHC and RHIC. Ref. [1] R. Paatelainen, K.J. Eskola, H. Holopainen and K. Tuominen, Multiplicities and p_T spectra in ultrarelativistic heavy ion collisions from a next-to-leading order improved perturbative QCD + saturation + hydrodynamics model. Phys. Rev. C 87 (2012) 044904. Ref. [2] R. Paatelainen, K.J. Eskola, and H. Niemi, work in progress. Ref. [3] K.J. Eskola, K. Kajantie, P.V. Ruuskanen, K. Tuominen Scaling of transverse energies and multiplicities with atomic number and energy in ultrarelativistic nuclear collisions. Nuc. Phys. B 570 (2000) 379. Ref. [4] I. Helenius, K.J. Eskola, H. Honkanen and C.A. Salgado, Impact-Parameter Dependent Nuclear Parton Distribution Functions_ EPS09s and EKS98s and Their Applications in Nuclear Hard Processes. JHEP 1207 (2012) 073.Speaker: Risto Paatelainen (Jyvaskyla University)
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13:00
Lunch break
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Parallel talks - Session 3A
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73
Energy-momentum tensor correlators in hot Yang-Mills theoryThe transport coefficients of hot QCD plasma, in particular the bulk and shear viscosities, have attracted a lot of attention in recent years. They can be defined through the infrared limits of the corresponding spectral functions, which, however, are notoriously complicated to determine non-perturbatively. In this talk, I will present recent perturbative results for the bulk and shear thermal correlators in SU(N) Yang-Mills theory, computed to next-to-leading order (NLO) in the coupling. The results are used for direct comparisons with lattice and gauge/gravity predictions for Euclidean correlators as well as to verify and refine known sum rules for the quantities. In addition, we will argue that obtaining accurate information on the UV behavior of the bulk and shear spectral functions will one day aid a more precise lattice determination of the corresponding viscosities.Speaker: Yan Zhu (Bielefeld University)
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QCD Reggeon Field Theory from JIMWLK/KLWMIJ EvolutionWe discuss how the high energy QCD evolution generated by the KLWMIJ Hamiltonian can be cast in the form of the QCD Reggeon Field Theory. We suggest a natural way of defining the Pomeron and other Reggeons in the framework of the KLWMIJ evolution and derive the QCD Reggeon field Theory Hamiltonian which includes several lowest Reggeon operators. This Hamiltonian generates evolution equations for all Reggeons in the case dilute-dense scattering, including the nonlinear BK equation for the Pomeron.Speaker: Tolga Altinoluk (U)
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Plasma instabilities and particle production in GlasmaPlasma instabilities play important roles in thermalization processes of relativistic heavy-ion collisions. We study early-stage instabilities of non-Abelian plasma on the basis of two-particle irreducible(2PI) formalism. In this presentation, We focus on Nielsen-Olesen instability caused by homogeneous but time dependent color magnetic field. For this purpose, We perturbatively solve equations of motion of gluon fields and Scwinger-Dyson (Kadanoff-Baym) equation simultaneously up to 1-loop level. Our results imply that exponential growth of unstable modes directly leads to explosive particle production. Futhermore, the longitudinal fluctuation of gluon fields is found to generate secondary instabilities of all momentum modes in an analytic way.Speaker: Shoichiro Tsutsui (Kyoto University)
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Non-Gaussian initial conditions for evolution of observables in high-energy collisionsThe proper description of the initial states of heavy ion collisions requires complete understanding of the partonic structure of the participants in the process. The essential role in the high-energy nuclear wave-functions of the target and projectile is played by the small-x gluons whose behavior and interactions are studied by the Color Glass Condensate effective theory. We extend the effective McLerran-Venugopalan action for distribution of large-x sources by introducing an additional non-Gaussian term of fourth order in the density of color charges. The effects of the quartic term may explain the observed discrepancy between the MV model and the LHC data on charged hadron transverse momentum distribution and may give a theoretical explanation of the gamma modification contained in the AAMQS global fits. We also attempt to relate the observed KNO scaling law in particle multiplicity distributions to properties of soft gluons. Finally, we obtain an area law behavior for the magnetic Wilson loop in the first moment after the impact, using a Gaussian action, indicating that the structure of the chromo-magnetic fields might be represented as an uncorrelated magnetic vortex configuration.Speaker: Elena Petreska (Graduate Center/Baruch College CUNY)
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Gluon saturation beyond leading logsFor inclusive enough observables in DIS or pp or pA collisions, high energy leading logs are resummed thanks to the Balitsky-Kovchegov equation. I will discuss some effects appearing in this context beyond the strict leading log accuracy, such as the kinematical constraint or the running of the coupling.Speaker: Guillaume Beuf
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Scattering amplitude and pomeron loops in the perturbative QCD with large $N_c$The amplitude for the collision of two hadrons with the lowest order pomeron loop is calculated. Numerical calculations show that the loop contribution to the amplitude begins to dominate the single pomeron exchange at rapidities $8-10$. Full dependence of the triple-pomeron vertex on intermediate conformal weights is taken into account.Speaker: Prof. Mikhail Braun (S.Petersburg University)
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Parallel talks - Session 3B
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79
Generalized medium-induced gluon radiation and its coherence propertiesIn this work we improve existing calculations of radiative energy loss by computing corrections that implement energy-momentum conservation, previously only implemented a posteriori, in a rigorous way. Using the path-integral formalism, we compute in-medium splittings allowing transverse motion of all particles in the emission process, thus relaxing the assumption that only the softest particle is permitted such movement. This work constitutes the extension of the computation carried out for x → 1 in Phys. Lett. B718 (2012) 160-168, to all values of x, the momentum fraction of the energy of the parent parton carried by the emitted gluon. In order to accomplish a general description of the whole in-medium showering process, in this work we allow for arbitrary formation times for the emitted gluon (the limit of small formation times was previously employed in [J.-P. Blaizot, F. Dominguez, E. Iancu, and Y. Mehtar-Tani, JHEP1301 (2013) 143], for the g → gg splitting). We provide general expressions and their realisation in the path integral formalism within the harmonic oscillator approximation.Speakers: Liliana Apolinario (Universidade de Santiago de Compostela (ES)), Nestor Armesto Perez (Universidade de Santiago de Compostela (ES))
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Energy loss in unstable quark-gluon-plasmaThe quark-gluon plasma at the early stage of relativistic heavy-ion collisions is unstable due chromomagnetic plasma modes. The energy loss per unit path length of a fast parton scattering elastically in such a plasma is studied as an initial value problem. Although the approach is designed to study the unstable plasma, the well known results of equilibrium plasma are also reproduced. The energy loss in unstable QGP is shown to have strong time and directional dependence. Since the magnitude of the energy loss per unit length in an unstable QGP can be much bigger than in an equilibrium plasma, the problem is important for jet quenching in relativistic heavy-ion collisions.Speaker: Stanislaw Mrowczynski (Jan Kochanowski University, Kielce, Poland)
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A hybrid strong/weak coupling approach to jet quenchingWe study the interaction of high energy QCD jets with strongly coupled quark gluon plasma. We explore a hybrid approach, in which the high virtuality splitting processes that dominate the QCD shower proceed as in vacuum while the partons of the shower interact with the system as dictated by strongly coupled computations via the AdS/CFT correspondence. We discuss the Monte Carlo implementation of such approach and explore different implementation of the strongly coupled dynamics.Speaker: Mr Daniel Pablos (Universitat de Barcelona)
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Radiation spectrum of a massive quark-gluon antenna in a QCD mediumWe derive the radiation spectrum of a massive quark-gluon antenna in a QCD medium. The calculation is done in the formalism of the classical Yang-Mills (CYM) equations and interactions with the medium are handled in the harmonic oscillator approximation, valid for soft gluon emissions. We discuss the effect produced by the presence of a mass scale and compare the results with the massless case. We put our findings in relation with the energy loss of heavy quarks in heavy ion collisions, one of the phenomenological puzzles of RHIC and LHC data.Speaker: Mr Manoel Rodríguez Calvo (USC - IPhT CEA Saclay)
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Production of two heavy quark pairs in double parton scattering at LHCThe production of $c\bar{c}c\bar{c}$, $b\bar{b}b\bar{b}$ and $c\bar{c}b\bar{b}$ pairs in double parton scattering at LHC energies is investigated. We estimate the contribution of saturation effects to the different final states and predict the energy dependence of the cross sections. Moreover, we estimate the ratio between the double and single parton scattering cross sections for the full rapidity range of the LHC and for the rapidity range of the LHCb experiment. For the full rapidity range we confirm a previous prediction, namely that for charm production the double parton scattering contribution becomes comparable to the single parton scattering one at LHC energies. We also demonstrate that this result remains valid when one considers saturation effects in the calculations. We also show that the production of $c\bar{c}b\bar{b}$ contributes significantly to bottom production. For the LHCb kinematical range the ratio is strongly reduced.Speaker: Prof. Fernando Navarra (IFUSP)
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A state of the art lattice-QCD + Hadron-Resonance Gas Equation of StateWe present a state of the art QCD Equation Of State (EOS) in the limit of vanishing baryon density. Continuum-extrapolated lattice-QCD data with realistic quark masses by the Budapest-Wuppertal collaboration are employed in the high-temperature regime and are joined to a Hadron-Resonance Gas (HRG) EOS at lower temperatures. Since experimental data from heavy-ion collisions suggest that particle ratios are frozen before kinetic freeze-out, with two different temperatures describing the particle yields and the slope of pT-spectra, we offer the user the possibility of employing both a Chemical Equilibrium EOS and a more realistic Partial Chemical Equilibrium one, with resonant reactions allowed in the hadronic phase but with particle ratios fixed at the chemical freeze-out temperature. Parametrizations of the various thermodynamic quantities are offered to the user so that the whole setup can be easily implemented into existing hydrodynamic codes. A snapshot of preliminary results at non-vanishing baryon density will be possibly displayed.Speaker: Andrea Beraudo (Universita e INFN (IT))
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16:30
Coffee break
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Parallel talks - Session 4A
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85
Tilted initial state: reasons and consequencesThe latest experimental data from ALICE@LHC confirm that the hydrodynamic simulations of the ultra-relativistic heavy ion collisions are very successful in describing these reactions. One of the most important elements of such a hydrodynamic model is the initial state for further hydro evolution. Unfortunately at the moment there is no unambiguous model describing the initial states of energetic heavy ion collisions, and thus all initial states in use are either completely phenomenological or contain some phenomenological elements. In my talk I will argue that from very general principles, like linear and angular momentum conservation, we can expect to form tilted and rotating initial state. I will present initial states generated by the Effective String Rope model [1] for RHIC and LHC heavy ion reactions; and compare it with some other models which intend to calculate initial states for hydrodynamic simulations. Then I will address the most important question - what are the consequences of such a tilted and rotating initial state for further evolution of the fireball, and how it can be confirmed/reconstructed from the observables.Speaker: Volodymyr Magas (University of Barcelona)
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86
Collective excitations in anistropic quark-gluon-plasmaThe quark-gluon plasma at the early stage of relativistic heavy-ion collisions is strongly anisotropic. We systematically study spectrum of collective excitations of such a plasma which is a fundamental characteristic of any many-body system. We demonstrate how the spectrum evolves when the momentum distribution of plasma constituents changes from the extremely prolate – infinitely elongated along the beam direction, through the isotropic one to the extremely oblate – infinitely squeezed in the beam direction. We discuss when unstable modes show up and when they disappear; their role in the plasma dynamics is also considered.Speaker: Katarzyna Deja (National Centre for Nuclear Research)
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Bulk and Shear Viscosity Effects in Event-by-Event Relativistic Hydr odynamicsBulk and shear viscosity effects on the collective flow harmonics in heavy ion collisions are investigated, on an event by event basis, using a newly developed 2+1 Lagrangian hydrodynamic code named v-USPhydro which implements the Smoothed Particle Hydrodynamics (SPH) algorithm for viscous hydrodynamics. Bulk viscosity is shown to enhance the collective flow Fourier coefficients from v2(pT) to v5(pT) when pT∼1−3 GeV even when the bulk viscosity to entropy density ratio, ζ/s, is significantly smaller than 1/(4π) while shear viscosity has an opposite effect.Speaker: Frederique Grassi
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88
Relativistic viscous hydrodynamic modeling of the Quark-Gluon Plasma with ECHO-QGPWe will present ECHO-QGP (Eulerian conservative higher-order code for QGP), a new (3+1)-dimensional numerical code developed by our team, implementing second-order relativistic viscous hydrodynamics and conceived for the study of the Quark-Gluon Plasma created in heavy ion collisions. ECHO-QGP features second-order treatment of causal relativistic viscous effects both in Minkowski and in Bjorken coordinates; complete or partial (i.e. with particle ratios fixed at the chemical freeze-out) chemical equilibrium before kinetic freeze-out can be imposed on the EOS for the hadronic phase. We provide initialization routines based both on the optical and on the Monte-Carlo (suited to the simulation of event-by-event fluctuating initial conditions) implementation of the Glauber model. Freeze-out is modeled according to the Cooper-Frye prescription. A snapshot of the several tests performed for the validation of the code will be presented: results always appear accurate, as guaranteed by the combination of the conservative (shock-capturing) approach and the high-order methods employed. Some physics results for particle spectra and flow will be displayed. Finally, we shall extend our investigation to the case of fluctuating lumpy initial conditions, illustrating the ECHO-QGP potentiality to address event-by-event hydrodynamic simulations of nucleus-nucleus (A-A) and proton-nucleus (p-A) collisions, with particular emphasis on the role played by viscosity. References: 1. L. Del Zanna, V. Chandra, G. Inghirami, V. Rolando, A. Beraudo, A. De Pace, G. Pagliara, A. Drago, F. Becattini, arXiv:1305.7052[nucl-th]. 2. L. Del Zanna et al., Astro. Astrophys. 473, 11 (2007).Speaker: Dr Vinod Chandra (INFN Florence)
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The parton cascade BAMPS with the improved Gunion-Bertsch matrix elementAn updated version of the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS) is presented, which allows interactions among all partons: gluons, light quarks, and heavy quarks with elastic and inelastic collisions. We introduce the improved Gunion-Bertsch matrix element, which cures problems of the original Gunion-Bertsch result in characteristic regions of the phase space. Verified by extensive numerical calculations, the improved matrix element agrees well with the exact calculation. With the new matrix element, important properties of the quark-gluon-plasma in heavy-ion collisions such as the thermalization time of the plasma and the shear viscosity over entropy density ratio are calculated within the microscopic transport model BAMPS. Furthermore, we compare our results of the nuclear modification factor and elliptic flow to experimental data at RHIC and LHC.Speaker: Carsten Greiner (University of Frankfurt)
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Parallel talks - Session 4B
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90
CMS pA dijet measurementsThe results of the CMS dijet measurements in pPb collisions will be discussed. The dijet pt ratio measurements can provide a limit on the magnitude of a possible jet quenching effect in pPb collisions. We find that the jets are not significantly modified by final state interactions. The result from inclusive centrality measurements are in good agreement with theoretical predictions based on EPS09 nuclear parton distribution functions. However, the dijet pseudorapidity is found to vary significantly as a function of the event activity quantified by the energy deposited in the forward calorimeter. This observation along with other studies will be discussed in the context of the centrality determination. Different choices of centrality variables introduce different biases on the experimental observables. MC studies are useful in understanding these biases and to distinguish different effects.Speaker: Doga Can Gulhan (Massachusetts Inst. of Technology (US))
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Jet production and structure in pp, p-Pb and Pb-Pb collisions measured by ALICEOne of the major goals of jet and high transverse momentum measurements in heavy-ion collisions is to quantify the medium-modified fragmentation of hard scattered partons. Here, the motivation for the reconstruction of jets, as compared to single particle measurements, is to gain a larger sensitivity to the possibly modified structure of the parton shower. It aims at the understanding of the fundamental mechanisms of in medium energy loss and their relation to transport properties of the medium itself. The measurement of the jet production cross section in three different colliding systems pp (QCD vacuum), p-Pb (cold nuclear matter), and PbPb (hot partonic system) allows to extract the modification of jets in the hot and dense medium with respect to two references. We will present recent ALICE results on the jet production in pp, p-Pb and Pb-Pb collisions and discuss their sensitivity to a modified jet fragmentation process beyond leading parton energy loss and explore the impact of cold nuclear matter.Speaker: Jiri Kral (University of Jyvaskyla (FI))
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D-meson production in p-Pb collisions at the LHC with ALICEAt the beginning of 2013 ALICE collected data during the LHC p-Pb run at the energy of sqrt{sNN}=5.02 TeV. The measurement of D-meson production in this collision system is important to study the role of initial-state effects such as shadowing, saturation or k_T broadening. ALICE already measured a modification of the momentum distributions of charmed hadrons in central Pb-Pb collisions with respect to pp collisions providing evidence for heavy-quark energy loss in strongly interacting matter. To better quantify the effect of charm quark energy loss in the observed modification of the D-meson spectra in Pb-Pb, a precise characterization of the initial-state effects in cold nuclear matter is needed. D mesons have been reconstructed via their hadronic decay channels in the central rapidity region. The first measurement of the D0, D+, D*+ and Ds+ production cross sections in minimum bias p-Pb collisions and the transverse momentum dependence of their nuclear modification factors R_{pPb} will be presented.Speaker: Andrea Festanti (Universita e INFN (IT))
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93
On the energy dependence of the $D^+/D^-$ production asymmetryWe discuss the origin of the asymmetry present in $D$ meson production and its energy dependence. In particular, we have applied the meson cloud model to calculate the asymmetries in $D^-/D^+$ meson production in high energy $p-p$ collisions and find a good agreement with recent LHCb data. Although small, this non-vanishing asymmetry may shed light on the role played by the charm meson cloud of the proton.Speaker: Dr Marina Nielsen (Universidade de São Paulo)
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94
Estimation of electric conductivity of the quark gluon plasma via asymmetric heavy-ion collisionsWe show that in asymmetric heavy-ion collisions, especially off-central Cu+Au collisions, a sizable strength of electric field directed from Au nucleus to Cu nucleus is generated in the overlapping region, because of the difference in the number of electric charges between the two nuclei. This electric field would induce an electric current in the matter created after the collision, which result in a dipole deformation of the charge distribution. The directed flow parameters $v_1^{\pm}$ of charged particles turn out to be sensitive to the charge dipole and provide us with information about electric conductivity of the quark gluon plasma.Speaker: Yuji Hirono (The University of Tokyo)
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90
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