Table of contents

The 4th Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus–nucleus Collisions (Hot Quarks 2010) was held in La Londe-Les-Maures, France, from June 21–26, 2010. Following the traditions of the conference, this meeting gathered more than 70 participants in the first years of their scientific careers. The present issue contains the proceedings of this workshop.

The articles published in this volume clearly show the presence of a dynamic new generation of physicists interested in the different aspects of high energy nuclear collisions. The newest results from RHIC at Brookhaven and SPS at CERN were presented, as well as the latest results from the proton–proton programme from the LHC at CERN, while waiting for the data of the lead–lead collisions only available some months after the meeting. Along with these experimental findings, the corresponding theoretical research was also extensively discussed as well as the new perspectives for future facilities like FAIR, EIC and LHeC.

We wish to thank the sponsors of the Hot Quarks 2010 Conference, who supported the authors of this volume: IN2P3/CNRS (France), EMMI (Germany), Institut Pluridisciplinaire Hubert Curien (France), National Science Foundation (USA), CERN (Switzerland), Helmholtz International Center for FAIR (Germany), Xunta de Galicia (Spain) and the Journal of Physics G.

Markus Bleicher (Frankfurt (HIC4FAIR), Germany) Helen Caines (Yale University, USA) Manuel Calderon de la Barca Sanchez (UC Davis, USA) Alessandro de Falco (Cagliari/INFN, Italy) Rainer Fries (Texas A & M University, USA) Raphael Granier de Cassagnac (Ecole Polytechnique, France) Boris Hippolyte (IPHC, Strasbourg, France) Andre Mischke (Utrecht University, The Netherlands) Marzia Nardi (Torino/INFN, Italy) Carlos A Salgado (Universidade de Santiago de Compostela, Galicia, Spain)

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The CERN Large Hadron Collider (LHC) started operation a few months ago. The machine will deliver proton-proton and nucleus-nucleus collisions at energies as high as = 14 TeV and luminosities up to ~ 10³⁴ cm⁻²s⁻¹ never reached before. The main open scientific questions that the seven LHC experiments - ATLAS, CMS, ALICE, LHCb, TOTEM, LHCf and MOEDAL - aim to solve in the coming years are succinctly reviewed.

The ALICE experiment, designed primarily for studying heavy-ion collisions at the Large Hadron Collider, has several features in its apparatus that allow it to contribute significantly to the first proton–proton physics. ALICE started proton–proton data taking at the end of 2009: data collected at a centre-of-mass energy of 0.9, 2.36 and 7 TeV allowed several first physics studies to be carried out. In this contribution, the first measurements of the charged-particle pseudorapidity density at the three energies will be presented. These measurements have been obtained using mainly the two innermost layers of the inner tracking system. The reconstruction algorithm and the analysis procedure are described and the results are compared to other measurements and model predictions.

With the large acceptance and excellent granularity of its tracking system, the CMS experiment is well-equipped to explore the bulk properties of the quark-gluon plasma with the first Pb+Pb collisions recorded at the LHC. Given the twenty-fold increase in collision energy compared to previous experiments, CMS measurements will be a powerful test of parton saturation, jet quenching, and hydrodynamic models, which have been successful in describing many features of particle production at RHIC. In preparation for early measurements of charged multiplicity, transverse-momentum spectra, and two-particle angular correlations, the corresponding measurements performed on p+p collision data are reviewed.

The electromagnetic calorimeters, PHOS (PHOton Spectrometer) and EMCAL (Electro-Magnetic CALorimeter) have been designed for photon detection and jet measurement in ALICE experiment at LHC. We discuss the strategy adopted for calorimetric π⁰ measurements via the π⁰ → 2γ channel in ALICE and present the two-photon invariant mass spectra obtained in p+p collisions at .

This article presents the ratio of the yields of antiprotons to protons in pp collisions as measured by the ALICE experiment at = 0.9 and 7 TeV. The ratio is measured to be R_|y|<0.5 = 0.957 ± 0.006(stat.) ± 0.014(syst.) at 0.9 TeV and R_|y|<0.5 = 0.991 ± 0.005(stat.) ± 0.014(syst.) at 7 TeV independent of both rapidity and transverse momentum. The results are compared with theoretical predictions.

The method used by ALICE to measure identified charged hadron spectra in the Inner Tracking System (ITS) is presented. The analysis results are compared with measurements using the Time Projection Chamber and Time-of-Flight detector at larger transverse momentum.

ALICE is the LHC experiment mainly dedicated to the study of hot and high energy density nuclear matter created in heavy-ion collisions. ALICE has also developed a detailed proton-proton physics programme, in order to exploit its capabilities to investigate the novel energy regime made available by LHC, which turns out to be quite interesting in itself besides being important as a baseline for the heavy-ion data. Results will be presented of the ϕ resonance measurements done with the first data sets taken at LHC between 2009 and 2010, in pp collisions at 900 GeV. ϕ transverse momentum spectra and global yields will be shown.

Non-extensive thermodynamics is a novel approach in high energy physics. In high-energy heavy-ion, and especially in proton-proton collisions we are far from a canonical thermal state, described by the Boltzmann-Gibbs statistic. In these reactions low and intermediate transverse momentum spectra are extremely well reproduced by the Tsallis-Pareto distribution, but the physical origin of Tsallis parameters is still an unsettled question.

Here, we analyze whether Tsallis-Pareto energy distribution do overlap with hadron spectra at high-pT. We fitted data, measured in proton-proton (proton-antiproton) collisions in wide center of mass energy range from 200 GeV RHIC up to 7 TeV LHC energies. Furthermore, our test is extended to an investigation of a possible -dependence of the power in the Tsallis-Pareto distribution, motivated by QCD evolution equations. We found that Tsallis-Pareto distributions fit well high-pT data, in the wide center of mass energy range. Deviance from the fits appears at p_T > 20–30 GeV/c, especially on CDF data [7]. Introducing a pT-scaling ansatz, the fits at low and intermediate transverse momenta still remain good, and the deviations tend to disappear at the highest-pT data.

We investigate the gluon radiation pattern of a quark-antiquark pair traversing a dense QCD medium at high energy. We show that the medium-induced gluon radiation spectrum is logarithmically divergent and that the angular distribution exhibits an anti-angular ordering of soft-gluon emissions in contrast with angular ordering in in-vacuum radiation.

Preliminary results from the STAR collaboration of the azimuthal anisotropy (v2) of π0 and direct photon (γdir) at high transverse momentum (pT) from Au+Au collisions at center-of-mass energy = 200 GeV are presented. A shower-shape analysis is used to select a sample free of direct photons (π0) and a sample rich in direct photons γrich. The relative contribution of background in the γrich sample is determined assuming no associated charged particles nearby γdir. The v2 of direct photons (vγdir2) at mid-rapidity (|ηγdir| < 1) and high pT (8 < pγdirT < 16 GeV/c) is extracted from those of π0 and neutral particles measured in the same kinematic range. In mid-central Au+Au collisions (10–40%), the v2 of π0 (vπ02(pT)) and charged particles (vch2(pT)) are found to be ~ 0.12 and nearly independent of pT. The measured vγdir2(pT) is positive finite and systematically smaller than that of π0 and charged particles by a factor of ~ 3. Although the large vπ02 at such high pT might be partially due to the path-length dependence of energy loss, the non-zero value of vγdir2 indicates a bias of the reaction plane determination due to the presence of jets in the events. Systematic studies are currently in progress.

Jet fragmentation in p+p and Au+Au collisions is studied via back-to-back correlations of direct photons and charged hadrons. The direct photon correlations are obtained by statical subtraction of the background from decay photons. Results on the nuclear modification to the associated charged hadron yields are reviewed. Further studies of jet fragmentation in p+p using isolated direct photons are also presented. A k_T -smeared LO pQCD calculation is used to interpret the data. The sensitivity of the data to the underlying fragmentation function is tested and the results are found to be compatible with expectations of a sample dominated by quark jet fragmentation.

Employing a microscopic transport model we investigate the evolution of high energetic jets moving through a viscous medium. For the scenario of an unstoppable jet we observe a clearly strong collective behavior for a low dissipative system η/s ≈ 0.005, leading to the observation of cone-like structures. Increasing the dissipation of the system to η/s ≈ 0.32 the Mach Cone structure vanishes. Furthermore, we investigate jet-associated particle correlations. A double-peak structure, as observed in experimental data, is even for low-dissipative systems not supported, because of the large influence of the head shock.

We present a study of the performance of jet reconstruction algorithms for Pb+Pb collisions at = 5.52 TeV based on a full GEANT simulation of the ATLAS detector. It is shown that ATLAS can provide measurements that are sensitive to different in-medium energy loss scenarios leading to the jet quenching. The capability of measurements of fragmentation function and j_T distribution are presented. We concentrate on some biases in these measurements that might be due to the detector effects or to the choice of a jet finding algorithm.

The ALICE collaboration is interested in measuring the ξ = ln(p^jet_T/p^hadron_T) distribution of hadrons in jets known as the Hump-backed plateau (HBP). After an introduction to color coherence effects responsible for the shape of the HBP, we discuss the ALICE capabilities to perform such a study. Preliminary results from ALICE for non corrected charged particle and jet spectra measurement in p+p collisions at = 900 GeV and 7 TeV are presented. Finally, we show the results of a MC based analysis of intrajet radiations. It supports the idea of jet collimation which increases with increasing jet energy as expected from QCD and show the feasability of this study with ALICE.

Full jet reconstruction in heavy-ion collisions is a promising tool for the quantitative study of properties of the dense medium produced at RHIC. Measurements of d+Au collisions are important to disentangle initial state nuclear effects from medium-induced k_T broadening and jet quenching. Study of jet production and properties in d+Au in combination with similar studies in p+p is an important baseline measurement needed to better understand heavy-ion results. We present mid-rapidity inclusive jet p_T spectra and di-jet correlations (k_T) in 200 GeV p+p and d+Au collisions from the 2007–2008 RHIC run. We discuss the methods used to correct the data for detector effects and for background in d+Au collisions.

We investigate whether and how different fragmentation properties of quarks and gluons affect identified particle spectra. We present a systematic study of π K and p production in minimum bias (inelastic, non-diffractive), two- and three-jet events at RHIC, Tevatron and LHC energies. Through the study of two- and three-jet events and various jet-production channels we can directly access the fragmentation properties of quark and gluon jets. We present Monte-Carlo estimate for the contribution of quark and gluon jets to individual particle species spectra, that can be compared to experimental results and test our current knowledge of the physics behind particle production inside jets.

Jet-matter interaction remains a central question and a theoretical challenge in heavy-ion physics and might become important in high-multiplicity events in proton-proton collisions at LHC energies. Full jet measurement at LHC offer the proper tool to investigate energy loss process and fragmentation of hard parton in the medium. Since jet reconstruction will be constrained to small cone sizes, then study of the connection between jets and surrounding environment provides a further possibility to extend our exploration. We study jets at = 14 TeV and pp collisions at = 7 TeV. We analyze the flavor components in jet-like environments. We introduce a definition for surrounding cones/belts and investigate flavor dependence and correlation of different hadron species produced in jets. Here, we focus on proton-triggered correlations. Our analysis can be extended for heavy ion collisions.

Dihadron correlations in nuclear collisions continue to serve as an important tool for accessing energy loss and medium modification of jet shapes and yields, particularly in comparison to p+p reference data. However, there remain unsettled issues in the methodology and interpretation of dihadron correlations. In particular, the disentanglement and subtraction of event anisotropy from a correlated and (possibly highly quenched) jet signal in a large heavy-ion background is not a closed case. A new technique for reducing background in a triggered correlation analysis is to require trigger particles to reside within the cone radius of a reconstructed jet. A simulation study of the influence of background on dihadron correlations is presented together with improvements afforded by using jet reconstruction for purity enhancement of trigger particles. Additionally, progress using these techniques in Au+Au data from the STAR detector is reported along with discussion of their relation to existing results.

Charm and bottom quarks have been proposed as probes to study partonic matter produced in high-energy heavy-ion collisions. The detailed understanding of the production mechanisms in proton-proton collisions is of considerable interest as a QCD test tool and as reference calibration for heavy-ion studies. Measurements of the D meson yield in jets probe the production processes in which the observed D mesons are formed primarily from gluon splitting into c or b pairs. The charm content in jets is calculable in perturbative QCD, and the leading non-perturbative correction is expected to be significant at LHC energies. In this contribution we present a performance study of the reconstruction of charged D^*± mesons in jets based on the first data collected by the ALICE experiment in minimum bias p+p collisions at = 7 TeV . D^*+ mesons are reconstructed through the decay sequence D^*+ → D⁰π⁺ and D⁰ → K⁻π⁺ (and its charge conjugate channel).

The status of the charged multi-strange baryon analysis at LHC energies is presented. This report is based on the results obtained with ALICE (A Large Ion Collider Experiment), profiting from the characteristic cascade-decay topology. A special attention is drawn to the early pp data-taking period (2009–2010) and subsequently, on the uncorrected p_T-spectra extracted at mid-rapidity for centre of mass energies of 0.9 TeV and 7 TeV.

We present preliminary results on strangeness and dilepton production in Ar+KCl reactions at 1.76 AGeV. For the first time an ω signal could be extracted in heavy-ion collisions in this energy region. Furthermore we find a strong enhancement of yield in the low invariant lepton pair mass region over an elementary reference suggesting the onset of non trivial effects of the medium. This hint is supported by a nearly complete vanishing of the OZI suppression of the ϕ to ω ratio which is characteristic for elementary reactions.

Two particle correlations are used to extract information about the characteristic size of the system for proton-proton collisions at =900 GeV measured by the ALICE (A Large Ion Collider Experiment) detector at CERN. The correlation functions obtained show the expected Bose-Einstein effect for identical particles, but there are also long range correlations present that shift the baseline from the expected flat behavior. A possible source of these correlations is the conservation of energy and momentum, especially for small systems, where the energy available for particle production is limited. A new technique, first introduced by the STAR collaboration, of quantifying these long range correlations using energy-momentum conservation considerations is presented here. It is shown that the baseline of the two particle correlation function can be described using this technique.

Event-by-event fluctuations and correlations in azimuthal angle are currently widely investigated in various experiments. In this paper the Φ measure (earlier used in experiments to evaluate fluctuations in p_T) is now applied to azimuthal angle ϕ. Properties of this Φ_ϕ function are investigated through fast generators and with complex models. Preliminary results of NA49 on Φ_ϕ are also presented.

The problem of early thermalization of matter produced in relativistic heavy-ion collisions at RHIC is discussed in the framework of a hybrid model that consists of the transverse-hydrodynamics stage followed by the standard perfect-fluid hydrodynamics stage and freeze-out. The two hydrodynamic regimes are connected with the help of Landau matching conditions. A satisfactory description of the soft hadronic observables is achieved. This indicates that the early-thermalization problem and also the HBT puzzle may be to large extent circumvented.

The recent results on heavy flavor at the Relativistic Heavy Ion Collider will be reviewed. The results on charm cross section, heavy flavor collectivity and energy loss, color screening effect and quarkonia production mechanism will be highlighted. Precise measurements with future detector upgrades will be discussed.

Quarkonia production can be used to investigate the properties of the dense matter produced in heavy-ion collisions at RHIC because the production is theorized to be suppressed due to the Debye color screening of the potential between the heavy quarks. Lattice calculations indicate that a sequential suppression of quarkonia states in heavy-ion collisions will give us a model dependent measurement of the temperature of the Quark Gluon Plasma (QGP). Suppression is determined by calculating R_AA, which is the ratio of the production in p+p scaled by the number of binary collisions to the production in Au+Au. The Υ states are of particular interest because at 200 GeV the effects of recombination and co-mover absoprtion are smaller than for J / ψ, which lowers the systematic uncertainty of the interpretation of the R_AA calculation. It is also important to consider cold nuclear effects, which can be determined from d+Au collisions. We will present our results for mid-rapidity Υ production in p+p, as well as our preliminary results in d+Au and Au+Au at = 200 GeV. These results will then be compared with theoretical QCD calculations.

The Forward Muon Spectrometer of the ALICE experiment is designed for the study of quarkonium resonances and open heavy flavour particles coming from the strongly interacting matter produced in nucleus-nucleus collisions at the LHC, where the formation of the Quark Gluon Plasma is expected. Muon pairs are detected at forward rapidity (−4 < y < −2.5) and in a wide transverse momentum range (from 0 to tens of GeV/c). The proton-proton physics program of the Muon Spectrometer has the aim to define a proper normalization for nuclear collision studies and to deal with some open issues such as quarkonium production mechanism and polarization. The physics performances of the Muon Spectrometer for charmonium studies are presented and the progress of the data taking with the first LHC high energy run is shown.

Production, elliptic flow and the nuclear modification factor of charm and bottom quarks are studied in central and non-central heavy-ion collisions at RHIC and LHC using the partonic transport model Boltzmann Approach of MultiParton Scatterings (BAMPS). Employing an initial heavy quark yield obtained with PYTHIA the full space-time evolution of charm and bottom quarks in the quark-gluon plasma (QGP) is carried out with BAMPS, taking also secondary production in the QGP into account. Only elastic collisions of heavy quarks with particles from the medium cannot describe the experimentally observed elliptic flow and nuclear modification factor. However, using an improved Debye screening and the running coupling yields a result which is much closer to data.

The stochastic dynamics of heavy quarks in the fireball produced in heavy-ion collisions is followed through numerical simulations based on the Langevin equation. The modification of the final p_T spectra (R_AA) of c and b quarks, hadrons and single-electrons with respect to pp collisions is studied. The transport coefficients are evaluated treating separately the contribution of soft and hard collisions. The initial heavy-quark spectra are generated according to NLO-pQCD, accounting for nuclear effects through recent nPDFs. The evolution of the medium is obtained from the output of two hydro-codes (ideal and viscous). The heavy-quark fragmentation into hadrons and their final semileptonic decays are implemented according to up-to-date experimental data. A comparison with RHIC data for non-photonic electron spectra is given.

The energy loss of heavy quarks in the hot and dense matter created at RHIC, can be used to probe the properties of the medium. Both charm and beauty quarks contribute to the non-photonic electrons through their semi-leptonic decays. It is essential to determine experimentally the relative contribution of charm and beauty quarks to understand the suppression of heavy flavors at high P_T in central Au+Au collisions. The azimuthal angular correlations of non-photonic electrons with the reconstructed D⁰ allow to disentangle the contribution of charm and beauty and to reduce the background below the D⁰ invariant mass as well. We discuss the STAR measurement of non-photonic electron and D⁰ → Kπ azimuthal correlations in p+p collisions at 200 GeV. Furthermore, we show results from the application of microvertexing techniques for charm and beauty searches in Cu+Cu and Au+Au collisions at 200 GeV using the information of the Silicon tracker of STAR.

Direct photon spectra are calculated within a transport+hydrodynamics hybrid approach, in which the high-density part of the transport evolution has been replaced by a 3+1-dimensional hydrodynamic calculation. We study the effects of changing the parameters of the two interfaces between the transport- and hydrodynamic descriptions on the resulting direct photon spectra.

The properties of γ-jet pairs emitted in heavy-ion collisions provide an accurate mean to perform a tomographic measurement of the medium created in the collision through the study of the medium modified jet properties. The idea is to measure the distribution of hadrons emitted on the opposite side of the direct photon. The feasibility of such measurements is studied by applying the approach on the simulation data, we have demonstrated that this method allows us to measure, with a good approximation, both the jet fragmentation and the back-to-back azimuthal alignment of the direct photon and the jet. Comparing these two observables measured in pp collisions with the ones measured in AA collisions reveals the modifications induced by the medium on the jet structure and consequently allows us to infer the medium properties. In this contribution, we discuss a first attempt of such measurements applied to real proton-proton data from the ALICE experiment.

The production of prompt photons at high transverse momentum in proton-proton collisions (p-p) is a useful tool to study perturbative Quantum-Chromo-Dynamics (pQCD). In particular, they yield valuable information about parton distribution functions in the proton. The experimental measurement of prompt γ is a difficult task due to the large background of decay photons from neutral mesons, mainly π⁰. We present a full simulation and reconstruction study of prompt γ identification in p-p at = 14 TeV in the ALICE electromagnetic calorimeter EMCal, giving details on the methods developed to separate them from decay photons with the help of shower-shape and isolation cuts. We present Monte Carlo predictions for signal and background. The method used to extract the final isolated γ corrected cross-section is presented and the calculation of various experimental corrections is outlined.

We study the spectrum of multi-photon radiation off a fast quark in medium in the BDMPS/ASW approach. We reproduce the medium-induced one-photon radiation spectrum in dipole approximation, and go on to calculate the two-photon radiation in the Molière limit. We find that in this limit the LPM effect holds for medium-induced two-photon ladder emission.

Measurements of π⁰ and η inclusive spectra provide reference data for upcoming heavy ion runs, as well as a check on the applicability of perturbative QCD calculations at LHC energies. The high-resolution central tracking system of ALICE can be used to reconstruct π⁰ and η through photon conversions, as an alternative to direct measurement in the ALICE Calorimeters. Knowledge of the ALICE material budget is crucial for the extraction of the absolute yield from the conversion technique. The statistics availible from this technique are comparable to that of the photon spectrometer (PHOS), and the reconstruction method can also be applied for Pb-Pb collisions. Moreover, the implementation of a photon conversion trigger in the High Level Trigger (HLT) framework gives the possibility of identifying π⁰ and η candidates online, and increasing the statistics at higher momentum. The status of the π⁰ meson reconstruction from photon conversions from p-p collisions at = 900 GeV and = 7 TeV is presented in this article.

We propose to study the quarkonia (ϕ) propagation in the QGP. We are especially interested in the elastic and inelastic scattering process of these quarkonia in the medium. We developed the Bethe-Salpeter formalism to calculate the elastic cross section (σ_elas) for ϕ – gluon/hadron. Results obtained in this work show that σ_elas(ϕ – gluon/hadron) might have non negligible effects in the study of Q propagation.

Di-muons are especially relevant to study the properties of the strongly interacting QCD matter created in Pb+Pb collisions at the LHC, since they are produced at early times and propagate through the medium, mapping its evolution. Simulations of CMS di-muon measurements in such an environment are presented in this paper. In particular, we show that CMS has very good detection conditions for the studies of J/ψ and Υ production, with an excellent di-muon mass resolution and a rather good acceptance. CMS will also be able to measure Z⁰ production in heavy ion collisions for the first time. Early corresponding p+p measurements are reviewed as they will serve as the baseline for the heavy ion measurements.

The NA60 experiment has studied low-mass muon pairs production in proton-nucleus collisions at 400 GeV/c at the CERN SPS. The mass spectrum is well described by the superposition of the two-body and Dalitz decays of the light neutral mesons η, ρ, ω, ή and ϕ. The large collected statistics allows to isolate the contributions due to the Dalitz decays of the η and ω mesons, from which the electromagnetic transition form factors of the two mesons have been extracted. The found values agree with the previous available measurements, improving their uncertainty thanks to the higher statistics. The results thus confirm the discrepancy with the prediction of the Vector Meson Dominance model in the case of the electromagnetic form factor of the ω meson.

We study dielectron production in proton-proton collisions at top RHIC beam energy within an extended statistical hadronization model. The invariant mass spectrum of correlated dielectron pairs is evaluated in the low invariant mass region and calculated results are compared with the PHENIX experiment. The model is found to be able to describe the data very well up to invariant masses of 1 GeV with few adjustable parameters.

We analyse dilepton emission from hot and dense hadronic matter using a hybrid approach based on the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model with an intermediate hydrodynamic stage for the description of heavy-ion collisions at relativistic energies. Focusing on the enhancement with respect to the contribution from long-lived hadron decays after freeze-out observed at the SPS in the low mass region of the dilepton spectra (often referred to as "the excess"), the relative importance of the emission from the equilibrium and the non-equilibrium stages is discussed.

The transverse momentum (P_T) and centrality dependence of the azimuthal anisotropy (v₂) are measured for charged hadron species at 62.4 and 200 GeV in Cu + Cu and Au + Au collisions by the PHENIX experiment at RHIC. The results are consistent with eccentricity scaling and with quark number (n_q) + transverse kinetic energy (KEt) scaling. Also, we found that v₂ divided by the participant eccentricity of the initial geometry proportionally increases with the number of participants to the 1/3 power except at small N_part in Cu+Cu at = 62.4 GeV. Taking these scalings (n_q, KE_T, eccentricity and N^1/3_part) into account, there is a universal scaling for v₂ with different energies, collision sizes and particle species. The results indicate that v₂ is determined by more than just the geometrical eccentricity and also depends on the size of the collision. Moreover, using blast wave fitting, we report that both the behaviors of v₂ and P_T distributions can be understood from the thermal nature of produced particles based on hydro-dynamical behavior.

We would like to formulate relativistic dissipative hydrodynamics for multi-component systems with multiple conserved currents. This is important for analyses of the hot matter created in relativistic heavy ion collisions because particle creations and annihilations of various particle species are frequently taking place there. We show that consistent formulation in such systems involves many non-trivialities, and derive constitutive equations that satisfy Onsager reciprocal relations and describe the systems without ambiguity.

The azimuthal anisotropy of charged particle emission in heavy ion collisions is a sensitive probe of the properties and the dynamical evolution of the produced matter. The systematic study of elliptic flow (v₂), and higher order harmonics can yield information about the equilibration timescale, the nuclear equation of state and the viscosity in the different stages of the system evolution, as well as the initial state conditions of the heavy ion collisions. Experimentally, it is important to be able to reconstruct the flow using different methods, since they have different sensitivity to non-flow correlations and fluctuations which affect the extracted signal. In CMS, the nuclear reaction plane can be determined independently using several different detector subsystems. The reconstruction of elliptic flow using calorimetry and the tracking system is presented.

Using ideal and viscous hydrodynamics, the ratio of azimuthal moments v₄(v₂)² is calculated for pions, protons, and kaons in = 200A GeV Au+Au collisions. For any value of viscosity here is little dependence on particle species. Ideal hydrodynamics and data show a flat curve as a function of pt. Adding viscosity in the standard way destroys this flatness. However, it can be restored by replacing the standard quadratic ansatz for δf (the viscous correction to the distribution function at freeze-out) with a weaker momentum dependence.

STAR measurements of v₁ for identified particles for Au+Au collisions at = 200 GeV are presented. A negative v₁ slope is observed for pions, protons, antiprotons and kaons (K⁰_S) in 10-70% central collisions. For pion v₁ slope, the comparison between the current result and available models (RQMD, UrQMD, AMPT, QGSM and hydro model with a tilted source) is made. In 5-30% central collisions, surprisingly sizable difference between v₁ of protons and antiprotons is observed. The centrality and energy dependence of proton v₁ are also presented. The charged hadron v₁ for Cu+Cu collisions at = 22.4 GeV is measured and compared with results obtained previously.

Proton-proton collisions at LHC energies reach a multiplicity density comparable to nuclear collisions at lower energy. It is therefore natural to ask whether the collective bulk behavior observed in heavy-ion collisions develops already in p-p collisions. In previous experiments, the study of p_t distributions of identified particles in the framework of blast wave models provided considerable insight on the collective behavior and on the freeze-out parameters of the fireball created in heavy-ion collisions. These ideas have recently been applied also to p-p collisions at RHIC. The ALICE experiment, thanks to its excellent PID capabilities and p_t coverage, offers an ideal test-bench for these studies at the LHC. In this work, we discuss the performance and analysis strategy of ALICE for blast wave studies and present some preliminary results on identified particle spectra, based on the data collected in the late 2009.

The azimuthal anisotropy of charged particles in heavy ion collisions is an important probe of quark-gluon plasma evolution at early stages of reaction. Now, with the start of Large Hadron Collider (LHC), the collective effects in proton-proton collisions are also of great interest. In this work we analyze the ability of different methods to extract elliptic flow in pp collisions at LHC. The analysis is based on Monte Carlo simulations of proton-proton collisions with PYTHIA, PHOJET and EPOS event generators at energies = 900 GeV and 7TeV.

The Super Proton Synchrotron (SPS) at CERN covers one of the most interesting regions of the phase diagram (T - μ_B) of strongly interacting matter. The study of central Pb+Pb collisions by NA49 indicate that the threshold for deconfinement is reached already at the low SPS energies. Theoretical considerations predict a critical point of strongly interacting matter at energies accessible at the SPS. The NA61/SHINE experiment, a successor of the NA49 project, will study hadron production in p+p, p+A, h+A, and A+A reactions at various energies. The broad physics program includes the investigation of the properties of strongly interacting matter, as well as precision measurements of hadron spectra for the T2K neutrino experiment and for the Pierre Auger Observatory and KASCADE cosmic-ray projects. The main physics goals of the NA61/SHINE ion program are to study the properties of the onset of deconfinement at low SPS energies and to find signatures of the critical point of strongly interacting matter. To achieve these goals a broad range in the (T - μ_B) phase diagram will be covered by performing an energy (10A-158A GeV/c) and system size (p+p, B+C, Ar+Ca, Xe+La) scan. The first data for this 2-D scan were taken in 2009, i.e. p+p interactions at 20, 30, 40, 80, 158 GeV/c beam energy. This contribution will summarize physics arguments for the NA61/SHINE ion program, show the detector performance and present the current status of the experiment and plans for the next years.

The nuclear matter, deconfined quark matter, and Quarkyonic matter in low temperature region are classified based on the 1/N_c expansion. The chiral symmetry in the Quarkyonic matter is investigated by taking into account condensations of chiral particle-hole pairs. It is argued that the chiral symmetry and parity are locally violated by the formation of chiral spirals, . An extension to multiple chiral spirals is also briefly discussed.

We compute and discuss the temperature-dependence of the shear viscosity, focusing on that around the critical point, using the Nambu–Jona-Lasinio model in the leading order of 1/N_c expansion and the chiral limit. Our calculation is based on a systematic resummation method of the singular diagrams, developed recently by the present authors. In the leading order of the theory, 2 → 2 scattering between quark-quark, antiquark-antiquark and quark-antiquark contributes to the shear viscosity. The ratio of the shear viscosity to the entropy, η/s, decreases as temperature increases, only with a tiny cusp at T = T_c.

The QCD critical point can be found in heavy ion collision experiments via the non-monotonic behavior of many fluctuation observables as a function of the collision energy. The event-by-event fluctuations of various particle multiplicities are enhanced in those collisions that freeze out near the critical point. Higher, non-Gaussian, moments of the event-by-event distributions of such observables are particularly sensitive to critical fluctuations, since their magnitude depends on the critical correlation length to a high power. We present quantitative estimates of the contribution of critical fluctuations to the third and fourth moments of the pion and proton, as well as estimates of various measures of pion-proton correlations, all as a function of the same five non-universal parameters. We show how to use nontrivial but parameter independent ratios among these more than a dozen fluctuation observables to discover the critical point. We also construct ratios that, if the critical point is found, can be used to overconstrain the values of the non-universal parameters.

A brief review of the phenomenological studies in the field of heavy ion collisions based on the Color Glass Condensate theory and, in particular, of those relying in the use of the BK equation including running coupling effects is presented.

Global perturbative QCD analyses, based on large data sets from electron-proton and hadron collider experiments, provide tight constraints on the parton distribution function (PDF) in the proton. The extension of these analyses to nuclear parton distributions (nPDF) has attracted much interest in recent years. nPDFs are needed as benchmarks for the characterization of hot QCD matter in nucleus-nucleus collisions, and attract further interest since they may show novel signatures of non- linear density-dependent QCD evolution. However, it is not known from first principles whether the factorization of long-range phenomena into process-independent parton distribution, which underlies global PDF extractions for the proton, extends to nuclear effects. As a consequence, assessing the reliability of nPDFs for benchmark calculations goes beyond testing the numerical accuracy of their extraction and requires phenomenological tests of the factorization assumption. Here we argue that a proton-nucleus collision program at the LHC would provide a set of measurements allowing for unprecedented tests of the factorization assumption underlying global nPDF fits.

We describe a model for low x DIS off nucleons and nuclei which provides initial conditions for QCD evolution that satisfy unitarity at low-x. We discuss it's extension to the perturbative regime and it's predictions for several DIS observables. We emphasize the well-known connection between rise of the diffractive cross section at high energies and nuclear shadowing.

The physics of the initial conditions of heavy ion collisions is dominated by the nonlinear gluonic interactions of QCD. These lead to the concepts of parton saturation and the Color Glass Condensate (CGC). We discuss recent progress in calculating multi-gluon correlations in this framework, prompted by the observation that these correlations are in fact easier to compute in a dense system (nucleus-nucleus) than a dilute one (proton-proton).

We present the results from global fits of inclusive DIS experimental data using the Balitsky-Kovchegov equation with running coupling.

Recent results on the suppression of hadrons at forward rapidities from the STAR collaboration indicate that high gluon densities play an important role in the initial conditions of heavy-ion collisions. The study of these initial conditions is therefore crucial in the next stage of understanding and quantifying the data from RHIC and the LHC. The best way to perform these measurements is through Deep Inelastic Scattering measurements on nuclei. Currently, there are no accelerator facilities which are able to perform this measurement. In this paper, I will outline the latest developments of the eRHIC proposal at BNL as well as preliminary designs of a new detector as well as an assessment of the current detectors (PHENIX and STAR) abilities to run in an eRHIC era.

We have measured pt-dependent two-particle number correlations on azimuth and pseudorapidity for eleven centralities of = 62 and 200 GeV Au-Au collisions at STAR. 2D fits to these angular correlations isolate the azimuth quadrupole amplitude, denoted 2v²₂{2D}(p_t), from localized same-side correlations. Event-plane V₂(p_t) measurements within the STAR TPC acceptance can be expressed as a sum of the azimuth quadrupole and the quadrupole component of the same-side peak. V₂{2D}(p_t) can be transformed to reveal quadrupole pt spectra which are approximately described by a fixed transverse boost and universal Levy form nearly independent of centrality. A parametrization of V₂{2D}(p_t) can be factored into centrality and p_t-dependent pieces with a simple p_t dependence above 0.75 GeV/c. Results from STAR are compared to published data and model predictions.

We study the chiral phase transition by the non-equilibrium propagation of the sigma field. A quark fluid acts as a heat bath in local thermal equilibrium and evolves fluid dynamically. We allow for dissipative processes and fluctuations since the sigma field is propagated according to a Langevin-type equation of motion. Non-equilibrium fluctuations at the first order phase transition lead to an increase in the intensity of sigma excitations.

Physical observables in relativistic heavy ion collisions are determined by various multi-particle production mechanisms. The simultaneous model treatment of different collective nuclear effects at high energies (such as a hard multi-parton fragmentation in hot QCD-matter, thermal resonance production, hydrodynamical flows, etc.) is actually a rather complicated task. We discuss the simulation of the above effects by means of the Monte-Carlo model HYDJET++.

We introduce a transport approach at fixed shear viscosity to entropy ratio η/s to study the generation of collective flows in ultra-relativistic heavy-ion collisions. Transport theory supplies a covariant approach valid also at large η/s and at intermediate transverse momentum p_T, where deviations from equilibrium is no longer negligible. Such an approach shows that at RHIC energies a temperature dependent η/s enhances significantly the v₄/v²₂ respect to the case of constant η/s. Furthermore if NJL chiral dynamics is self-consistently implemented we show that it does not modify the relation between v₂ and η/s.

We investigate bulk and shear viscosities of the gluon plasma within relaxation time approximation to an effective Boltzmann-Vlasov type kinetic theory by viewing the plasma as describable in terms of quasigluon excitations with temperature dependent self-energies. The found temperature dependence of the transport coefficients agrees fairly well with available lattice QCD results. The impact of some details in the quasigluon dispersion relation on the specific shear viscosity is discussed.