# Heavy Ion Collisions in the LHC Era

Asia/Ho_Chi_Minh
Quy Nhon, Vietnam

#### Quy Nhon, Vietnam

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Description
Heavy Ion Collisions in the LHC Era will focus on the physics of proton-nucleus and nucleus-nucleus collisions at RHIC and LHC energies. Results accumulated by the RHIC/LHC experiments and recent theoretical developments will be presented on the following topics:
• A: Global and Collective Dynamics
• B: Jet quenching
• C: Heavy Flavor and Quarkonia Production
• D: Electroweak Probes
• E: QCD at High Temperature and Density & Phase Diagram
• F: Pre-equilibrium and Initial State Physics

We will aim to achieve a balance between review talks given by recognised specialists, and shorter contributions, special emphasis being placed on active participation by younger researchers and post-docs. Parallel sessions are foreseen, and are being organised as the need arises.

This will be part of a series of international meetings held regularly in Vietnam, created by Jean Tran Thân Van in 1993. Their purpose is to stimulate the development of advanced research in Vietnam and more generally in South East Asia, and to establish collaborative research networks with Western scientific communities. All sessions take place in the Seagull Hotel, where participants are also lodged. Meals are served in the hotel to all participants.

### Financial support

The conference is supported in part by the ExtreMe Matter Institute EMMI at GSI, Darmstadt (Germany), the grant PARTONPROP from the French funding agency ANR, and the European funding agency ERC.

Participants
• Andreas Ipp
• Che-Ming Ko
• Christoph Blume
• Elena Gonzalez Ferreiro
• Francois Arleo
• Gastao Krein
• Guillaume Beuf
• Hao Qiu
• Hirotsugu Fujii
• Hyunchul Kim
• Ilkka Helenius
• In-Kwon Yoo
• Jean Tran Thanh Van
• Jean-Paul Blaizot
• Jian-Xiong Wang
• Jorge Casalderrey Solana
• Kazunori Itakura
• Klaus Werner
• Lamia Benhabib
• Livio Bianchi
• Marcella Bona
• Marcus Bluhm
• Marlene Nahrgang
• Masayuki Asakawa
• Nestor Armesto
• Ngoc Diep Pham
• Nicole Bastid
• Pasquale Di Nezza
• Pengfei Zhuang
• Qun Wang
• Rajeev S. Bhalerao
• Sangyong Jeon
• Sarah Campbell
• Shougaijam Somorendro singh
• Shusu Shi
• Sourendu Gupta
• Stephane PEIGNE
• Takafumi Niida
• Tapan Nayak
• William Llope
• yogesh Kumar
• Monday, 16 July
• 09:00 12:30
Opening Session

This session will gather the participants of both confererences (on BSM and heavy-ion physics). Three pedagogical overview seminars will be given.

• 09:00
Conference opening 30m
• 09:30
Coffee break and late registration 45m
• 10:15
Overview on HEP in summer 2012 45m
Speaker: Greg Landsberg (Brown University (US))
• 11:00
New results and Perspectives in Heavy Ion Physics 45m
Speaker: Jean-Paul Blaizot (IPhT Saclay)
• 11:45
Results from Daya Bay 30m
Speaker: Harry Themann (Stony Brook)
• 12:30 14:00
Lunch 1h 30m
• 14:00 17:00
Pre-equilibrium and Initial State Physics
Conveners: Guilherme Teixeira De Almeida Milhano (Instituto Superior Tecnico (PT)), Kazunori Itakura (KEK)
• 14:00
Small-x physics at RHIC and LHC 30m
Speaker: Tapan Nayak (Department of Atomic Energy (IN))
• 14:30
Strong field physics as probe of early-time dynamics of heavy-ion collisions 30m
Speaker: Kazunori Itakura (KEK)
• 15:00
Forward particle productions in proton-nucleus collisions at the LHC 30m
We present the current theory status on the particle productions in the forward region in proton-nucleus collisions based on the Color Glass Condensate framework. We use the factorized formula, where the proton is described with the collinear parton distributions while the nuclear side with the unintegrated gluon distributions (uGD). The uGD is obtained from the x-evolution equations and parameters are fixed by Albacete et al. using HERA data.The transverse geometry of the target is described with the random sampling of the nucleons with Woods-Saxon distribution.
Speaker: Hirotsugu Fujii (University of Tokyo)
• 15:30
Coffee break 30m
• 16:00
Unstable dynamics of Yang-Mills fields at early times of heavy ion collisions 30m
The quark gluon plasma as produced in heavy ion collisions is exposed to early anisotropies in momentum space due to its rapid expansion. Such anisotropies can lead to unstable gluonic modes that can grow exponentially fast. In this talk, I present the 3+1 dimensional simulations of non-Abelian plasma instabilities. The simulations are based on gaugecovariant Boltzmann-Vlasov equations that include the Yang-Mills fields for gauge group SU(3). A turbulent cascade forms in the strong-ﬁeld regime, which is associated with an approximately linear growth of energy in collective ﬁelds.
Speaker: Andreas Ipp (V)
• 16:30
Gluon saturation at higher orders and improvement of kinematics 30m
The first part of the talk will be a brief overview of some recent theoretical progresses about DIS and pA processes within the Color Glass Condensate effective theory and related formalisms, in particular concerning higher order calculations. Then, I will present new results concerning the improvement of the treatment of kinematics in high-energy evolution equations like the Balitsky-Kovchegov equation. This amounts to perform a resummation of the largest spurious corrections appearing at each perturbative order in the Regge limit.
Speaker: Dr Guillaume Beuf (Universidade de Santiago de Compostela)
• Tuesday, 17 July
• 09:00 12:30
QCD at High Temperature and Density & Phase Diagram
• 09:00
Physics across the phase diagram of QCD 30m
Speaker: Sourendu Gupta (TIFR)
• 09:30
Studies on the QCD Phase Diagram at SPS and FAIR 30m
Speaker: Christoph Blume (Johann-Wolfgang-Goethe Univ. (DE))
• 10:00
Search for a Possible QCD Critical Point in the RHIC Beam Energy Scan using the STAR Experiment 30m
At the sqrt(sNN)=200 GeV top beam energy of the Relativistic Heavy Ion Collider (RHIC), collisions of two 197-Au nuclei result in dense and strongly interacting systems of partons at high temperatures, T, and low baryo-chemical potentials, muB. In central collisions, these systems hadronize at (muB,T) values near (~20,~160) MeV via a crossover-type transition. Systems formed at larger values of the baryo-chemical potential may undergo a first-order transition. This implies the possible existence of a critical point. Nuclear systems passing through such a critical point are expected to exhibit divergences of the thermodynamic susceptibilities and correlation lengths that are analogous to those seen in many liquids. The observation of a Quantum ChromoDynamic (QCD) critical point would transform the phase boundaries in (muB,T) space. Increasing the baryo-chemical potential in Lattice QCD calculations is computationally difficult, but it can be accomplished experimentally by reducing the beam energy. In the year 2010 and 2011 runs, the RHIC provided Au+Au collisions at seven beam energies ranging from 7.7 to 200 GeV, which spanned a range of muB from ~20 to ~420 MeV. The spectra and event-by-event multiplicities of numerous species of charged hadrons were measured in the wide and azimuthally complete acceptance of the Solenoidal Tracker at RHIC (STAR) experiment. The (muB,T) values at chemical freeze-out for the different beam energies and collision centralities can be inferred from the spectra. The shapes of the event-by-event multiplicity distributions, quantified by their statistical moments, mean, variance, skewness, and kurtosis, are expected to diverge non-monotonically as a result of the divergence of the correlation length expected if the system has passed close to the critical point. In this talk, we will present the status of the STAR Collaboration's exploration of the QCD phase diagram. This will include the study of the identified particle yield ratios to extract the (muB,T) values, and the statistical moments of the multiplicity distributions of several different species of charged hadrons. The particle identification is performed using the ionization energy loss in the Time Projection Chamber and the information from the then newly installed Time of Flight system. The moments values will be compared to the "baseline" behavior implied by the Hadron Resonance Gas model and Poisson statistics.
Speaker: Prof. W.J. Llope (Rice University)
• 10:30
Coffee break 30m
• 11:00
QCD end point, charge fluctuations, and final state interactions 30m
In this talk, we examine some of proposed experimental signals for the QCD end point and QCD phase transition. We then argue that final interaction effects are very important in relating physical quantities around the end point or in the quark-gluon plasma to experimental observables. Finally, we show that it is possible to reconstruct baryon number cumulants at chemical freezeout from observed proton number cumulants.
Speaker: Masayuki Asakawa (Osaka University)
• 11:30
Isospin Matter 30m
Speaker: Pengfei Zhuang (Tsinghua University)
• 12:30 14:00
Lunch 1h 30m
• 14:00 14:30
Future facilities
• 14:00
Physics at low xBj and in eA at the LHeC 30m
I will present the project of an electron-proton/ion collider at CERN using the LHC beams, the Large Hadron Electron Collider. After a brief introduction, I will present the project. Then I will summarize the possibilities for small-x studies and for electron-nucleus collisions. I will conclude with the status of the project and future steps to be taken.
Speaker: Nestor Armesto Perez (Universidade de Santiago de Compostela (ES))
• 14:30 16:30
Electroweak Probes
• 14:30
Modeling the Impact Parameter Dependence of the nPDFs With EKS98 and EPS09 Global Fits 30m
Speaker: Ilkka Helenius (University of Jyväskylä)
• 15:00
CMS results on electroweak boson production in pp and PbPb collisions 30m
Speaker: Lamia Benhabib (Ecole Polytechnique (FR))
• 15:30
Coffee break 30m
• 16:00
Thermal Photons in PHENIX 30m
Thermal radiation emitted by the quark-gluon plasma provides information on the initial temperature of the collision and thermalization of the QGP. Experimentally it is difficult to separate thermal photons from the measured direct photon spectrum. In PHENIX, we measure direct photons in the central arm using two complementary methods, one with the electromagnetic calorimeter (EMC) and another with virtual photons extracted from the dielectron spectrum. Recent measurements with the EMC method have determined the direct photon spectrum out to 25 GeV and 22 GeV in p+p and Au+Au collisions respectively. At these high transverse momenta, photons emitted from hard processes dominate the direct photon spectrum and the measured QGP effects are minimal. The virtual photon method is able to measure direct photons at low pt where the thermal photons are expected to make up more of the direct photon yield. In Au+Au, the low pt virtual photon spectra lies above the T_{AA} scaled p+p spectrum while the d+Au spectrum is in agreement with the scaled p+p. This suggests enhanced thermal photon production in Au+Au and no corresponding cold nuclear matter production or suppression in d+Au. PHENIX's direct photon measurements in p+p, d+Au, Cu+Cu and Au+Au will be presented. The elliptic flow and extrapolated temperature of the Au+Au direct photons will also be discussed.
Speaker: Sarah Campbell (Iowa State University)
• Wednesday, 18 July
• 09:00 12:30
Heavy Flavor and Quarkonia Production
• 09:00
Heavy flavor and Quarkonia in heavy-ion collisions with CMS 30m
Quarkonia are especially important for diagnosing and characterising the quark-gluon plasma since they are produced at early times and propagate through the medium. The Compact Muon Solenoid (CMS) detector at the LHC is ideal to measure muon pairs from quarkonia in the high-multiplicity environment of nucleus-nucleus collisions. Taking this advantage, CMS has measured the nuclear modification factors of prompt J/psi, non-prompt J/psi from b-hadron decays and Y(1S) in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. From the 2010 data sample (7.28 inverse microbarns) large suppressions of all quarkonia states relative to pp were observed in central collisions. A larger suppression of Y(2S+3S) relative to Y(1S) were also observed in minimum bias events. During the 2011 heavy-ion run CMS has collected about a factor twenty more events compared with the 2010 run, which amounts 150 inverse microbarns. With high statistics CMS could analyze psi(2S) and Y(2S) and Y(3S) separately. These new results on the quarkonium production in heavy ions will be also presented in this presentation.
Speaker: Hyunchul Kim (Korea University (KR))
• 09:30
Heavy flavour and quarkonium measurements in Pb--Pb collisions at $\sqrt {s_{\rm NN}}$ = 2.76 TeV with ALICE 30m
The LHC heavy ion physics program aims at investigating the properties of strongly-interacting matter in extreme conditions of temperature and energy density where the formation of the Quark Gluon Plasma (QGP) is expected. In high-energy heavy ion collisions, heavy quarks and quarkonium states are regarded as efficient probes of the properties of the QGP as they are created on a very short time scale in initial hard scattering processes. ALICE, the only detector designed and optimized for heavy ion physics at the LHC, measures open heavy flavours and quarkonia at mid-rapidity through the semi-electronic channel/dielectron decay channels and at forward rapidity through the semi-muonic/dimuon decay channels. In addition, charmed mesons are also detected at mid-rapidity via their hadronic decay channel. After a short description of the experiment, the latest results on open heavy flavour and quarkonium nuclear modification and elliptic flow in Pb--Pb collisions at $\sqrt {s_{\rm NN}}$ = 2.76 TeV will be presented.
Speaker: Nicole Bastid (Univ. Blaise Pascal Clermont-Fe. II (FR))
• 10:00
Recent Heavy Flavor Results from ATLAS 30m
Speaker: Marcella Bona (Queen Mary, University of London)
• 10:30
Coffee break 30m
• 11:00
Quarkonium Production in pp collisions at RHIC and the LHC 30m
Speaker: Jianxiong Wang (Institute of High Energy Physics, Academia Sinica)
• 11:30
J/psi polarization in pp collisions with ALICE 30m
Speaker: Livio Bianchi (Universita e INFN (IT))
• 12:30 14:00
Lunch 1h 30m
• 14:00 18:00
Social excursion
• Thursday, 19 July
• 09:00 12:30
Heavy Flavor and Quarkonia Production
• 09:00
Heavy Flavor Results from STAR 30m
Speaker: Dr Hao Qiu (Lawrence Berkeley National Lab)
• 09:30
Influence of a realistic medium description including fluctuations on heavy quark observables 30m
The observation of strong jet quenching and of high-$p_T$ hadron suppression in relativistic heavy-ion collisions are striking experimental signatures for the formation of a deconfined QCD plasma in which partons suffer from medium-induced energy loss. In particular, heavy quarks represent key probes for revealing the properties of the produced matter. In this talk, we discuss the consequences of a realistic medium description with fluctuating initial conditions on heavy-quark observables. For this purpose, we combine our Monte-Carlo approach to heavy-quark in-medium propagation MC@sHQ [1] with the full 3+1 dimensional fluid dynamic expansion from EPOS [2]. This allows for a consistent treatment of both the heavy-quark production and the collisional and radiative processes leading to the in-medium energy loss of heavy quarks. On an event-by-event basis, we report on $R_{AA}$ and $v_2$ for D and B mesons for RHIC and LHC conditions and confront our results with recent experimental observations. The use of the lattice equation of state in the EPOS fluid dynamics allows us to study the nature of the effective degrees of freedom in the vicinity of the crossover transition [4], as a proportion of hadronic degrees of freedom above $T_c$ reduces the energy loss of heavy quarks. [1] P. B. Gossiaux and J. Aichelin, Phys. Rev. C 78 (2008) 014904 [2] K. Werner et al., arXiv:1203.5704, [3] P. F. Kolb and U. W. Heinz, In *Hwa, R.C. (ed.) et al.: Quark gluon plasma* 634-714 [4] C. Ratti et al., Phys. Rev. D 85 (2012) 014004
Speaker: Dr Marlene Nahrgang
• 10:00
J/psi and Upsilon production in proton-nucleus collisions: lessons from RHIC for the 2012 proton-lead LHC run 30m
Speaker: Elena Gonzalez Ferreiro (Universidad de Santiago de Compostela)
• 10:30
Coffee break 30m
• 11:00
Dynamical Quarkonia Suppression in a QGP-Brick 30m
Speaker: Jorge Casalderrey Solana (University of Barcelona (ES))
• 11:30
Quarkonia production in relativistic heavy ion collisions 30m
Using the hydrodynamic model to describe the dynamics of heavy ion collisions, we have studied quarkonia production in these collisions by including both their dissociation in initial cold nuclear matter and subsequently produced quark-gluon plasma [1-3]. For the latter, we used the screened Cornell potential and the next-to-leading order perturbative QCD to determine, respectively, their in-medium properties and dissociation cross sections. The theoretical results for the dependence of the quarkonia nuclear modification factors on the collision centrality as well as the quarkonia transverse momentum were compared with the experimentally measured values at SPS, RHIC and LHC. Useful information on the properties of quarkonia in the quark-gluon plasma has been obtained. References 1) T. Song, C. M. Ko, S. H. Lee, and J. Xu, J/psi production and elliptic flow in relativistic heavy ion Collisions”, Phys. Rev. C 83, 014914 (2011). 2) T. Song, K. Han, and C. M. Ko, Charmonium production in relativistic heavy-ion collisions", Phys. Rev. C 84, 034907 (2011). 3) T. Song, K. C. Han, and C. M. Ko, Bottomonia suppression in heavy ion collisions at RHIC and LHC", Phys. Rev. C 85, 014902 (2012).
Speaker: Prof. Ko Che-Ming (Texas A&M University)
• 12:00
J/Psi in nuclear matter 30m
Speaker: Gastao Krein (UNESP)
• 12:30 14:00
Lunch 1h 30m
• 14:00 17:00
Jet quenching and energy loss
• 14:00
Probing the medium with hard probes in ALICE 30m
Speaker: Dr Pasquale Di Nezza (INFN Frascati)
• 14:30
J/psi suppression in p-A from parton energy loss 30m
Speaker: Stephane Peigne
• 15:00
Color coherence in jet evolution 30m
• 15:30
Coffee break 30m
• 16:00
Radiative energy loss in absorptive media 30m
In theoretical studies of medium-induced energy loss, it is commonly accepted that the radiative energy loss contribution dominates over the collisional. In these approaches, however, the influence of a damping of bremsstrahlung quanta, leading to a finite lifetime of the latter, has so far been neglected. In this talk it is argued that in an absorptive and polarizable plasma the radiative energy loss becomes significantly affected, in particular, for charges with high initial energy [1]. This is because damping mechanisms in the absorptive medium may influence the formation of radiation itself, prominently, in the case of large formation times. In this case, any suppression of the associated radiation spectrum has to be attributed to absorption rather than to coherence effects [2]. [1] M. Bluhm, P. B. Gossiaux, J. Aichelin, Phys. Rev. Lett. 107, 265004 (2011). [2] M. Bluhm, P. B. Gossiaux, T. Gousset, J. Aichelin, arXiv:1204.2469 [hep-ph].
Speaker: Dr Marcus Bluhm (SUBATECH Nantes)
• 16:30
Probing cold and hot QCD matter through photon+Q production in p-A and A-A collisions 30m
Speaker: Francois Arleo (CERN)
• Friday, 20 July
• 09:00 12:30
Global and Collective Dynamics
• 09:00
Jets, Bulk Matter, and their Interaction in Heavy Ion Collisions at the LHC 30m
Speaker: Klaus WERNER (Subatech)
• 09:30
Recent results from ALICE 30m
Speaker: Prof. In-Kwon Yoo (Pusan National University)
• 10:00
The recent elliptic flow results at STAR 30m
In this talk, we will review the recent elliptic flow results at RHIC-STAR.
Speaker: Shusu Shi (CCNU)
• 10:30
Coffee break 30m
• 11:00
Higher Harmonics in Event-by-Event Viscous Hydrodynamics 30m
In this era of precision measurement in heavy ion collisions, it is becoming increasingly important that we characterize the flow patterns in each individual event. Such measurements can yield much more precise determination of QGP properties including, but not limited to the value of the shear viscosity. In this talk, I will report on McGill group's efforts in analyzing current RHIC and LHC data on higher harmonics using MUSIC - the event-by-event 3+1D viscous hydrodynamics code developed at McGill.
Speaker: Sangyong Jeon (McGill University)
• 11:30
Global and Collective Dynamics at PHENIX 30m
In order to study the properties of the hot and dense matter created by heavy ion collisions, various physics observables have been measured in RHIC and LHC, such as spectra, collective flow, HBT, and two particle correlations. Collective flow is a sensitive probe to access the early stage of the matter created by the collisions. Especially higher harmonic flow, which are primarily coming from the spatial fluctuation of the initial participant density, can provides the strong constraints for the initial condition and shear viscosity in hydrodynamics calculations. HBT measurement is a powerful tool to study the space-time evolution of particle emitting source and can provide the information on the spatial anisotropy of the source at freeze-out. The spatial anisotropy at freeze-out is created by the balance of the initial geometry, the collective flow and the life time of the source. To study the interaction between hard-scattered patrons and the hot and dense matter, two particle correlations have been measured. Recently, it is considered that higher harmonic flow is a possible source of "ridge" and "mach cone" observed in two particle correlations. Estimation and subtraction of the contribution from collective flow are needed to extract jet components from two correlation measurements. In this talk, we will present higher harmonic flow $v_{n}$ for charged hadrons and azimuthal HBT measurement in Au+Au 200GeV collisions at PHENIX. The relation between higher harmonic flow and spatial anisotropy at freeze-out measured by HBT will be discussed. Besides, we will also present the recent results of azimuthal hadron correlations with the subtraction of backgrounds from higher harmonic flow.
Speaker: Mr Takafumi for the PHENIX Collaboration Niida (University of Tsukuba (JP))
• 12:30 14:00
Lunch 1h 30m
• 14:00 15:00
Global and Collective Dynamics
• 14:00
New Relativistic Dissipative Fluid Dynamics from Kinetic Theory 30m
Speaker: Prof. Rajeev Bhalerao (Tata Institute of Fundamental Research)
• 14:30
Shear and Bulk Viscosities of a Gluon Plasma in Perturbative QCD 30m
We calculate the leading order shear and bulk viscosities, $\eta$ and $\zeta$,of a gluon plasma in perturbative QCD using different treatments for the matrix element of the $gg\leftrightarrow ggg$ (23) process. A comprehensive comparison of different treatments or models has been made. We find that the Gunion-Bertsch (GB) formula can provide a robust approximation to the exact matrix element for the 23 process. Our result for $\eta$ using the exact matrix element for the 23 process agrees with that of Arnold, Moore and Yaffe (AMY) at very weak couplings and is smaller than AMY's by about 10-20% at intermediate couplings, which is partly due to finite angle scatterings. We agree with the Arnold, Dogan and Moore's (ADM) leading order result for $\zeta$ within errors. A better understanding is provided for the equivalence between soft gluon bremsstrahlung in the center of mass frame in the 23 process and collinear splitting in the local rest frame in the leading order, which explains the agreement between the GB formula and AMY's treatment at weak couplings. We also generalize our result to a general $SU(N_{c})$ pure gauge theory and summarize the current status of the viscosity computations in QCD.
Speaker: Prof. Qun Wang (University of Science and Technology of China)
• 15:00 15:30
Coffee break 30m
• 15:30 16:15
Summary talk 45m
Speaker: Nestor Armesto Perez (Universidade de Santiago de Compostela (ES))
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