Table of contents

The 5th edition of the Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus–Nucleus Collisions (Hot Quarks 2012) was held in Copamarina, Puerto Rico from 14–20 October 2012. As in previous years, this meeting gathered more than 70 participants in the early years of their scientific careers. This issue contains the proceedings of the workshop.

As in the past, the Hot Quarks workshop offered a unique atmosphere for a lively discussion and interpretation of the current measurements from high energy nuclear collisions. Recent results and upgrades at CERN's Large Hadron Collider (LHC) and Brookhaven's Relativistic Heavy Ion Collider (RHIC) were presented. Measurements from the proton-led run at the CERN-LHC were shown for the first time at this meeting. Recent theoretical developments were also extensively discussed, as well as the proposals for future facilities such as the Facility for Antiproton and Ion Research (FAIR) at Darmstadt, the Electron-Ion Collider at Brookhaven, and the LHeC. The conference's goal to provide a platform for young researchers to learn and foster their interactions was successfully met.

We wish to thank the sponsors of the Hot Quarks 2012 Conference, who supported the authors of this volume: Brookhaven National Laboratory (USA), European Laboratory for Particle Physics CERN (Switzerland), European Research Council (EU), ExtreMe Matter Institute EMMI (Germany), Helmholtz International Center for FAIR (Germany), IN2P3/CNRS (France) and the European Research Council via grant #259612, Lawrence Berkeley National Laboratory (USA), Lawrence Livermore National Laboratory (USA), Los Alamos National Laboratory (USA), National Science Foundation (USA), and Netherlands Organization for Scientific Research (Netherlands).

The PDF also contains the conference poster.

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.

Relativistic heavy ion collisions allow one to study Quantum Chromodynamics (QCD) under extreme temperature and density conditions. A new form of matter formed at energy densities above ~ 1 GeV/fm³, Quark-Gluon Plasma (QGP), is predicted in Lattice QCD calculations. One of the most interesting experimental signatures of QGP formation is jet-quenching due to in-medium energy loss when hard-scattered partons pass through the QGP. Direct jet reconstruction in heavy ion collisions has opened a new era of precision studies of jet-quenching. In this summary talk, recent jet measurements in heavy ion collisions and their implications are reviewed and discussed.

We explore phenomenological signatures of light quark jet quenching within the AdS/CFT correspondence. Firstly, we note that the numerical studies indicate a linear path dependence of the instantaneous energy loss of light quarks modeled as falling strings. Secondly, we propose a phenomenological model for generic description of their energy loss and use it to compute the nuclear modification factor R_AA for light quarks in an expanding plasma with Glauber initial conditions. Comparing with the light hadron R_AA data at the LHC, a qualitative agreement is shown. Thirdly, we show how the observed quantitative disagreement can be partially alleviated by including the effects from higher derivative corrections to AdS₅.

High momentum jets and hadrons are important probes for the quark gluon plasma (QGP) formed in nuclear collisions at high energies. We investigate how fluctuations in the background density of the QGP and fluctuations in the spatial distribution of the hard process create azimuthal asymmetries of the high momentum hadron spectrum, described by the Fourier coefficients v_n, n > 0 . We estimate the coefficients up to v₆ in a simple energy loss model tuned to single inclusive hadron suppression.

The study of jets, collimated sprays of particles associated with hard partons, is an important tool in testing perturbative quantum chromodynamics (pQCD) and probing hot and dense nuclear matter created in high energy heavy-ion collisions. Jets enable the study of hard scatterings, fragmentation and hadronisation and their modification in the presence of a nuclear medium with respect to baseline vacuum measurements, which is acquired from jet measurements in proton-proton collisions.

We have analysed data from proton-proton collisions at = 7 TeV measured by the ALICE experiment at the LHC and reconstructed the inclusive spectra of charged particle jets at mid-rapidity using anti-k_T clustering algorithm. We present the jet spectra corrected for detector effects using several unfolding methods. Furthermore, we examine various properties of jets, such as their charged particle multiplicity and jet shapes.

Reconstruction of jets in high-energy heavy-ion collisions is challenging due to the large and fluctuating background coming from the underlying event. We report results on full jet reconstruction, obtained from data collected in 2011 by the ALICE detector at LHC for Pb-Pb collisions at = 2.76 TeV. The analysis makes use of the tracking system and the electromagnetic calorimeter. Signal jets, which come from hard scattered partons, are reconstructed using the anti-k_T jet finder algorithm. The average background is subtracted on a jet-by-jet basis to reduce the contribution to the jet reconstructed energy coming from the underlying event. The jet spectrum is corrected to account for fluctuations in the background momentum density and detector effects through unfolding.

Measurements of the suppression of high-p_T particles and the away-side jets from heavy-ion collisions at RHIC have shown that medium-induced energy loss affects partons produced in the early stage of a heavy-ion collision. At LHC energies the initial production cross-section is much higher, which allows jets to be reconstructed with a wide kinematic range. Measuring fully reconstructed jets by taking advantage of the ALICE Electromagnetic Calorimeter allows for a more differential investigation of the parton energy loss. Parton energy loss will allow us to access key observables of the hot, dense matter created in heavy ion collisions. The data presented was collected during the 2.76 TeV Pb-Pb runs, as well as baseline measurements from the 2.76 TeV pp run. The procedures used to reconstruct jets and extract them from a fluctuating background will be discussed. The procedure for quantifying the background with a limited acceptance will also be discussed. These results are compared to pp measurements and simulations.

The first measurement of the transverse momentum imbalance of isolated-photon-jet pairs and the modification of fragmentation function of the inclusive jets in relativistic heavy ion collisions are reported. The analysis uses data from PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair and corresponding to an integrated luminosity of 150 μb⁻¹ recorded by the CMS experiment at the LHC in 2011. For events containing an isolated photon with transverse momentum p_T > 60 GeV/c and an associated jet with p_T > 30 GeV/c, the photon-jet p_T imbalance is studied as a function of collision centrality and compared to pp data and PYTHIA calculations at the same center-of-mass energy. Using the p_T of the isolated photon as an estimate of the energy of the associated parton at production, this measurement allows an unbiased characterization of the in-medium parton energy loss. In addition, further study on the modification of jet fragmentation function was studied using inclusive jets with p_T > 100 GeV/c. Both show the gradual centrality dependence of jet energy loss and fragmentation function modification.

We present a study of the dijet suppression at RHIC using the parton cascade model. We examine the modification of the dijet asymmetry A_j and the fragmentation distributions z and j_T in terms of: ; the path length of leading and sub-leading jets; cuts on the jet energy distributions; jet cone angle and the jet-medium interaction mechanism. We have introduced a string hadronization model and present hadronic jet fragmentation distributions. We find that A_j is most sensitive to and less sensitive to the nature of the jet-medium interaction mechanism. The fragmentation distributions show jet modification and differentiate between elastic and radiative+elastic modes.

Jet quenching has been observed at both RHIC and LHC energies, indicating that partons lose energy as they traverse the medium. To probe the effects of this partonic energy loss, measurements of the angular correlations between fully reconstructed jets and charged tracks in Pb-Pb collisions are studied. Fully reconstructing a jet provides access to the kinematics of the initial hard scattering while allowing us to study the distribution of hadrons on the away side from the modified recoil jet. Here we present first measurements of jet-hadron correlations in pp collisions at =2.76 TeV and an outlook for Pb-Pb collisions. The jets in this analysis are reconstructed from the 2011 data set using both charged tracks and neutral energy measured in the ALICE tracking system and the electromagnetic calorimeter respectively.

Coherence between multiple emitters is one of the most remarkable properties of QCD jet physics in vacuum. In the presence of a QCD medium one expects that the coherence pattern between multiple emitters is affected. In this work we calculate the gluon emission spectrum off an "asymptotic quark" traversing a dilute QCD medium. When interferences between initial and final quark are included, the medium induced gluon distribution gets modified. The coherent, incoherent and soft limit of the medium induced spectrum are studied. In the soft limit we find an elegant and intuitive probabilistic interpretation. We comment on possible phenomenological applications of this setup for studying coherence effects on observables studied in high energy nuclear collisions.

I discuss recent results on the lattice with the main emphasis on the thermodynamics of the crossover region, restoration of the chiral symmetry and fluctuations of conserved charges as an indicator of deconfinement, that may also be used to determine the chemical freeze-out conditions in heavy-ion collision experiments.

We report the first measurements of azimuthal anisotropy at midrapidity originated from the dipole asymmetry due to fluctuations in the initial geometry in Au+Au collisions at = 200 GeV, based on data from the STAR experiment at the Relativistic Heavy Ion Collider. The signal is almost symmetric in pseudorapidity and we report it as a function of pseudorapidity and transverse momentum for different centrality. Results are compared with available model predictions.

Femtoscopic two-particle correlations carry important information about the particle emitting source. Of particular interest is the m_T dependence of extracted source radii, which is introduced by the dynamics of the system created in heavy-ion collisions. The reach in m_T of the traditional pion-pion correlation measurements is limited by the small rest mass of the examined particles. Thus, it can be extended with the analysis of pairs of heavier particles: kaons and protons, and proton-lambda pairs, being the heaviest system to extract source sizes so far. The excellent particle identification capabilities and high statistics datasets of ALICE allow to extract source radii differentially in transverse mass and provide new constraints on hydrodynamic models.

Azimuthal emission spectra of various hadron species in ultra-relativistic heavy ion collisions at ≈ 200 GeV exhibit a curious hierarchy at intermediate p_t (≈ 2 – 3 GeV). Rather than being ordered by mass, the spectra seem to be ordered by whether the species is a baryon or meson. It is seen that when the elliptic flow v₂ and transverse momentum p_T are both scaled by the number of quarks in each hadron, the spectra fall in line with each other. This number of constituent quark (NCQ) scaling suggests a system where the relevant degrees of freedom are colored partons as opposed to hadrons: the quark-gluon plasma (QGP). Thus, a break down of this scaling as beam energy is reduced could be indicative of the QGP threshold. However, at lower energies, there is also an increase in the number of entrance-channel partons transported to mid-rapidity due to baryon stopping, which can violate NCQ scaling even above the QGP threshold. We describe a specific pattern for the break down of the scaling that includes the observed difference in elliptic flow for positive and negative pions. We also contrast baryon stopping with the Chiral Magnetic Effect (CME)–an alternative model for π₊/π₋ flow difference–and discuss results from tests that can distinguish between them.

In 2010 and 2011, RHIC ran the first phase of a planned beam energy scan program to probe, among other things, the nature of the phase transition between hadrons and Quark Gluon Plasma as the matter vs anti-matter excess increases. Many experimental findings are now available from that scan. In this talk, I discuss the meaning of those results and the future plans and motivation for the second phase of the RHIC beam energy scan.

The most recent lattice results on the QCD phase diagram in the presence of a strong magnetic field strongly disagree with results from previous lattice simulations and several model calculations. The most remarkable difference is the qualitative behavior of the critical temperature as a function of the magnetic field intensity, which in later results are shown to decrease in opposition to what was found previously. According to the authors, such a discrepancy in lattice simulations could be due to different lattice spacing, or different number of flavors and quark masses. We investigate the influence of quark masses on the Polyakov-Quark-Meson model and show that, although quantitatively the results are sensitive to those parameters, the qualitative behavior remains the same.

The nuclear modification factors R_AA and R_CP have been used to measure medium-induced suppression in heavy-ion collisions at = 200 GeV which was among the earliest evidence for the existence of a strongly interacting medium called a quark-gluon plasma (QGP). Nuclear modification factors for asymmetric collisions (R_dA) have measured the Cronin Effect, an enhancement of high transverse momentum particle yields in deuteron-gold collisions relative to proton-proton collisions. A similar enhancement is observed in data presented in these proceedings and competes with the quenching caused by partonic energy loss in the QGP. In these proceedings we will present charged-hadron R_CP at mid-rapidity for = 7.7 – 62.4 GeV as well as identified π⁺, K⁺, and pR_CP. Comparisons to HIJING motivate possible methods for disentangling competing modifications to nuclear transverse momentum spectra.

In this article we discuss the issue of the quark to gluon ratio in the Quark Gluon Plasma (QGP). Our model to describe the QGP evolution is based on transport theory including the mean field dynamics described by a quasi-particle model.The last is able to take into account for the lattice QCD thermodynamics and implies a "chemical" equilibrium ratio between quarks and gluons strongly increasing as T approaches to the temperature of the phase transition T_c. We present first the tests performed in a fixed box to check that our code is able to reproduce the equilibrium ratio and then the results obtained for the simulations of ultra-Relativistic Heavy Ion Collisions (uRHIC's) at RHIC and LHC energies. We observe a rapid evolution from a gluon dominated initial state to a quark dominated plasma and we see that near T_c almost 80% of the particles composing the plasma are quarks. This has potentially a strong impact on several quantitative aspects of QGP probes and furnishes a justification to the coalescence hadronization model.

The AdS/CFT correspondence may offer new and useful insights into the non-perturbative regime of strongly coupled gauge theories such as Quantum Chromodynamics. Soft-wall AdS/QCD models have reproduced the linear trajectories of meson spectra by including background dilaton and chiral condensate fields. Efforts to derive these background fields from a scalar potential have so far been unsuccessful in satisfying the UV boundary conditions set by the AdS/CFT dictionary while reproducing the IR behavior needed to obtain the correct chiral symmetry breaking and meson spectra.

We present a three-field scalar parametrization that includes the dilaton field and the chiral and glueball condensates. This model is consistent with linear trajectories for the meson spectra and the correct mass-splitting between the vector and axial-vector mesons. We also present the resulting meson trajectories.

I give a brief overview of flow phenomena in relativistic heavy-ion collisions and the hydrodynamic models used to simulate these systems, aimed at new and young researchers, such as those attending the Hot Quarks 2012 conference.

Using a recursive solution of the Yang-Mills equation, we calculate analytic expressions for the gluon fields created in ultra-relativistic heavy ion collisions at small times τ. We have worked out explicit solutions for the fields and the energy momentum tensor up to 4th order in an expansion in τ. We generalize the McLerran-Venugopalan model to allow for a systematic treatment of averaged charge densities μ² that vary as a function of transverse coordinates. This allows us to calculate radial, elliptic and directed flow of gluon fields. Our results can serve as initial conditions for hydrodynamic simulations of nuclear collisions that include initial flow.

Using a partonic transport model we investigate the evolution of conical structures in ultrarelativistic matter. Using two different source terms and varying the transport properties of the matter we study the formation of Mach Cones. Furthermore, in an additional study we extract the two-particle correlations from the numerical calculations and compare them to an analytical approximation. The influence of the viscosity to the shape of Mach Cones and the corresponding two-particle correlations is studied by adjusting the cross section of the medium.

Measurements of 2D transverse momentum correlations on (p_t1, P_t2) from minimum-bias Au+Au collisions at = 200 GeV at STAR are presented and discussed. These correlations, formed from all charged particles with p_t ≥ 0.15 GeV/c, |η| ≤ 1, and 2π in azimuth, show a broad peak extending from p_t=0.5–4.0 GeV/c. The broad peak is observed in both like- and unlike-sign charge combinations and for same- and away-side relative azimuth angles. Interestingly, the peak in the data for away-side or back-to-back pairs persists even in more-central collisions, remaining at approximately the same p_t for all centralities. These data are compared to theoretical models and the p_t dependence of the same-side angular correlation structure.

In recent years, the measurement of harmonic flow coefficients v_n has provided important insight into the hot and dense matter created in heavy ion collisions at RHIC and LHC. These coefficients are now understood to reflect the hydrodynamic response of the produced medium to the collision geometry. Due to finite number of nucleons in the system, the collision geometry can fluctuate from one event to another, and hence measuring the full distribution of the event-by-event v_n coefficients can provide better insights on the nature of these fluctuations and possible non-linear effects in the hydrodynamic response. This proceeding presents the first measurements of the event-by-event v_n distributions for n=2–4 in Pb-Pb collisions at = 2.76 TeV with the ATLAS detector.

We discuss the build up of the elliptic flow v₂ in a transport approach at fixed viscosity. We point out that in the indermediate transverse momentum region flows are also sensitive to microscopic details of the cross section, while hydrodynamics suffers from large uncertainties due to the non-equilibrium correction to the distribution function. We show, exploring the temperature dependence of η/s, that a study of v₂ in a wide p_T range allows to understand the difference behind the collective flows at LHC respect to RHIC. In particular the transport approach provides a tool able to naturally describe the rise and fall and saturation of the v₂(p_T).

We apply a nonlinear flow response formalism to the recently measured event plane correlations. We find that the observed event plane correlations can be understood as a result of the averaged effect of linear and quadratic flow response.

The pseudorapidity density and anisotropic flow of charged-particles provide fundamental information about global variables and correlations in heavy-ion collisions. The pseudorapidity density is related to the energy available for particle production while the anisotropic flow is related to collective effects from interactions between these particles. Extending these measurements to very forward pseudorapidities yields information about the longitudinal expansion of the system. The first measurements performed at the LHC over more than 8 units of pseudorapidity are presented. The longitudinal scaling of the measurements is analyzed and comparison to models is performed.

We present the first measurement of the direct-photon elliptic flow v^γ,dir₂ in Pb-Pb collisions at = 2.76 TeV with data taken by the ALICE experiment at the LHC. The measurement provides evidence for a non-zero v^γ,dir₂ for 1 < p_T < 3GeV/c with a magnitude similar to the observed charged pion . In order to explain the large inverse slope parameter T_eff of the low p_T direct-photon spectrum observed at LHC and RHIC, recent hydrodynamical descriptions of the direct-photon production include a substantial portion of thermal photons from the hot plasma phase. As a consequence of the early production time, v^γ,dir₂ is expected to be small compared to hadrons. A large v^γ,dir₂ might lend support for a significant direct-photon emission from late stages of the system evolution where hadron flow has developed.

Interest in the development of the theory of fluctuating hydrodynamics is growing. Early efforts suggested that viscous diffusion broadens the rapidity dependence of transverse momentum correlations. That work stimulated an experimental analysis by STAR. We study the hydrodynamic evolution using second order causal viscous hydrodynamics including Langevin noise. We obtain a deterministic evolution equation for the transverse momentum density correlation function. We use the latest theoretical equations of state and transport coefficients to compute the STAR observables. The results are in excellent accord with the measured broadening. In addition, we predict features of the distribution that can distinguish 2nd and 1st order diffusion.

The first measurement of two-particle correlations in pPb collisions at a center-of-mass energy of 5.02 TeV is presented. The correlations are studied in azimuth, ϕ, and pseudorapidity, η, as a function of charged-particle transverse momentum, p_T, and multiplicity. A total of two million collisions are used in this analysis. A long range (2 < |Δη| < 4), near-side (Δϕ ≈ 0) ridge-like structure emerges in the two-particle Δη−Δϕ correlation functions of high-multiplicity events. This is the first time such a correlation has been seen in proton-nucleus collisions, which which resembles the correlations seen in a broad energy range of nucleus-nucleus collisions and in high-multiplicity proton-proton collisions at = 7 TeV. The correlation strength rises approximately linearly with multiplicity and has a maximum in the range of p_T = 1 – 1.5 GeV/c.

The large multiplicities at the LHC may permit flow harmonics to be determined on an event-by-event basis in Pb-Pb collisions. We extract these harmonics from event-by-event di-hadron correlations. Within a fine centrality bin, we find the correlation function varies substantially on an event-by-event basis beyond expectations from statistical fluctuations. This implies large fluctuations in the initial conditions occur for a given impact parameter. Such large fluctuations lead to some events being highly triangular or highly elliptical, where the angular correlation function is completely dominated by the respective second and third Fourier harmonics. We will show unfolded v₂ distributions for various centralities, and implications for our understanding of the initial conditions.

In this talk I consider the deconfining phase transition at nonzero temperature in a SU(N) gauge theory, using a matrix model. I present some results including the position of the deconfining critical endpoint, where the first order transition for deconfinement is washed out by the presence of massive, dynamical quarks, and properites of the phase transition in the limit of large N. I show that the model is soluble at infinite N, and exhibits a Gross-Witten-Wadia transition.

The influence of ground-state properties of nuclei on the initial state geometry of strongly interacting matter in relativistic heavy ion collisions is discussed. Self-orientation effect in very-high-multiplicity collisions of deformed nuclei is explained. Deformation and wave function of Au, Cu nuclei are discussed in connection to the initial excentricity simulations. Suggestion for colliding selected isotopes of Sm, Zr and Ru nuclei is presented.

We present an overview of the phenomenology and experimental results on open heavy-flavour and quarkonium production in heavy-ion collisions at RHIC and at the LHC.

We study heavy quark energy loss in a hot and dense nuclear matter in the framework of Langevin equation coupled to a (2+1)-dimensional hydrodynamic model. The classical Langevin framework is modified such that both quasi-elastic scattering and gluon radiation are incorporated. We provide good description of D meson suppression measured by the ALICE collaboration. We further investigate the angular correlation function of c pairs, and find that it can be potentially employed to distinguish different energy loss mechanisms of heavy quarks inside QGP.

ALICE is the LHC experiment dedicated to the study of the Quark Gluon Plasma (QGP) in high-energy nuclear collisions. Due to their large mass and their production at the early collision stage, heavy quarks (charm and beauty) are well-suited probes to study the properties of the QGP. The open charm baryon Λ_c is reconstructed in ALICE in the decay channels Λ_c⁺ → π⁺ + K⁻ + p and Λ_c⁺ → K⁰_S + p, exploiting both topological selections and particle identification. We report about the analysis strategy to observe the signal in pp collisions for both decay channels and then show the invariant mass plots where the Λ_c peak is clearly visible.

Heavy quarks produced in pp and heavy ion collisions are studied using heavy-flavour decay electrons and heavy-flavour mesons. Detailed understanding of the production processes and fragmentation of heavy quarks can be obtained by studying the azimuthal angular correlation of heavy-flavour hadrons. The azimuthal angular correlations of heavy-flavour mesons and charged hadrons can be used to disentangle charm and beauty-hadrons in pp collisions. In this contribution the fraction of electrons from beauty-hadron decays in the heavy-flavour decay electron yield is shown as well as the beauty production cross section in pp collisions at = 2.76 TeV. The measurements are compared to the predictions from next-to leading order perturbative QCD calculations. We also show the results from correlation analysis of charged D* mesons and hadrons performed using pp collision data at = 7 TeV.

Heavy quarks are produced in early partonic hard scatterings and experience the full history of a heavy-ion collision. Consequently heavy quarks are a good tool to study properties of the hot and dense medium. In proton-proton collisions, the study of the production of heavy quarks provides an important test for perturbative QCD and serves as a reference for heavy ion collisions. Heavy-flavour measurements in the semi-electronic channel are performed with ALICE at midrapidity. We present the measurement of the p_T-differential cross section in proton-proton collisions at = 7 TeV, and of the nuclear modification factor and elliptic flow in Pb-Pb collisions at = 2.76 TeV.

These proceedings present the D⁰, D⁺ and D^*+ meson v₂ measured by ALICE in Pb-Pb collisions at = 2.76 TeV with various methods (the standard event plane, the scalar product and the Q-cumulant) and in different centrality classes.

We present the measurements of the D^+s production in pp collisions at = 7 TeV and in Pb-Pb collisions at = 2.76 TeV performed in the central rapidity region with the ALICE detector through the reconstruction of the hadronic decay channel D⁺_s → ϕπ⁺ → K⁺K⁻π⁺. The ratios of the yields of D⁺_s and non-strange D mesons as a function of the transverse momentum are also shown for both pp and Pb-Pb collisions.

Heavy quarks are important probes to understand the properties of the Quark Gluon Plasma (QGP) created in the relativistic heavy-ion collision. The PHENIX measurement of electrons from heavy-flavor decays shows large flow and strong suppression in Au+Au collisions at 200 GeV [1][2], which is not well understood. In these proceedings, we will present both the new PHENIX heavy-flavor electron v₂ results in Au+Au collisions at 62.4 GeV collisions using the Hadron Blind Detector (HBD) and the latest PHENIX measurement of charm and bottom separately in p+p collisions at 200 GeV with the recently installed Silicon Vertex Track (VTX).

Quarkonium states are expected to provide essential information on the properties of the high-density strongly-interacting system formed in the early stages of heavy-ion collisions. In particular the J/ψ suppression via color screening is a direct consequence of deconfinement. ALICE is the LHC experiment specifically designed to study nucleus-nucleus collisions. The production of heavy quarkonium states is measured by ALICE down to zero transverse momentum via the μ⁺μ⁻ decay channel in the Forward Muon Spectrometer (2.5 < y < 4) and via the e⁺e⁻ decay channel in the central barrel at mid rapidity (|y| < 0.9). The analysis of the inclusive J/ψ production in Pb-Pb collisions at a center of mass energy per nucleon pair =2.76 TeV is presented. The inclusive J/ψ nuclear modification factor as a function of centrality, transverse momentum and rapidity is shown and compared to similar measurements by other experiments and to theoretical predictions. Finally, a hint of a low transverse momentum J/ψ yield excess, with respect to the expected hadronic channel production, is discussed.

The sequential suppression of the individual Υ states in PbPb collisions with respect to their yields in pp data has been measured. The PbPb and pp datasets used in these proceedings correspond to integrated luminosities of 150/μb and 230/nb, respectively, collected by the CMS experiment at the LHC at 2.76 TeV in 2011. The relative suppression of the excited Υ states has been measured with respect to the Υ(1S) ground state, expressed as a double ratio [Υ(nS)/Υ(1S)]_pbPb/[Υ(nS)/Υ(1S)]_pp. The absolute suppression of the Υ(nS) yields in PbPb relative to the yields in pp scaled by the number of nucleon-nucleon collisions, R_AA, is measured as a function of the collision centrality. Integrated over centrality, the R_AA values for Υ(1S), Υ(2S), and the upper limit of Υ(3S) R_AA are reported in this proceeding, which demonstrate the sequential suppression of the Υ(nS) states in PbPb collisions at LHC energies.

The production and space-time evolution of heavy quarks and J/ψ in the quark gluon plasma is studied within the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS). This framework allows interactions among all partons: gluons, light quarks and heavy quarks. Heavy quarks, in particular, interact with the rest of the medium via binary scatterings with a running coupling and a more precise Debye screening which is derived from hard thermal loop calculations. We compare our results of the elliptic flow and nuclear modification factor not only to experimental data of heavy flavor electrons at RHIC, but also to LHC data of heavy flavor electrons, muons, D mesons, and non-prompt J/ψ. Where no data is available yet, we make predictions for those observables. Furthermore, results on prompt J/ψ elliptic flow are reported for RHIC energy within the same framework, taking the dissociation as well as regeneration of J/ψ in the quark-gluon plasma into account.

The production of direct photons in pp collisions via Compton scattering and q annihilation leading order processes is of great interest to test pQCD predictions and also to study parton fragmentation. The fragmentation of the recoil scattered parton can be studied using correlation between the photon and the charged particles emitted in the opposite direction. We present the study of the parton fragmentation in pp collisions at = 7 TeV measuring the imbalance parameter . Furthermore, a first uncorrected direct photon spectrum measured with the ALICE electromagnetic calorimeter (EMCal) is shown. These measurements open the way to a straightforward comparison between pp and Pb-Pb collisions concerning parton fragmentation and direct photon production.

Electroweak gauge bosons W and Z, do not interact strongly, and thus constitute clean probes of the initial state of nucleus-nucleus collisions. The comparison of their production cross-sections in pp and in nuclear collisions provides an estimate of the nuclear parton distribution functions. Despite the low production cross section of weak bosons compared to other nuclear processes, the relatively clean signal of their leptonic decay channel allows their detection. This paper reports measurements of Z and W bosons, produced in PbPb and pp collisions both at nucleon-nucleon center of mass energy =2.76 TeV with the CMS detector. The Z boson yield and the nuclear modification factor (R_AA) corresponding to the integrated luminosity of 150 μb⁻¹ for PbPb collisions are presented. The search for W bosons has been performed in the muon plus neutrino channel, using the data sample with integrated luminosity of 7.2 μb⁻¹ for PbPb collisions. Event centrality an muon pseudorapidity dependencies are studied for the complete W candidate sample as well as samples separated by charge (W⁺ and W⁻).

In minimum-bias (0–80%) Au+Au collisions at = 200 GeV, the elliptic flow (v₂) measurements of di-electrons for the low mass region (M_ee < 1.1 GeV/c²) are presented. The differential v₂ as a function of transverse momentum in different mass regions are also reported. The simulated and measured v₂ of di-electrons are compared in the low mass region.

Dielectrons play an important role in heavy ion collisions since they are produced during all stages of the collision and interact only electromagnetically. The PHENIX experiment was upgraded with the Hadron Blind Detector which provides excellent background rejection by removing pairs from both partially reconstructed Dalitz decays and photon conversions. In these proceedings we will report on the results obtained from 2009 data in p+p collisions using the HBD as well as the Au+Au results obtained in 2010.

We report on the first dielectron measurement in pp collisons at = 7 TeV with the ALICE detector system. The results are compared to the expected hadronic sources. The hadronic cocktail agrees to the measured dielectron continuum within statistical and systematic uncertainties. The status of the dielectron measurement in Pb–Pb collisions at = 2.76 TeV is addressed.

Jet related observables have been some of the most powerful and exciting probes for understanding the matter produced in ultra-relativistic heavy ion collisions. Full jet reconstruction was begun at RHIC, and the LHC experiments have shown the power and kinematic reach of these observables. Here we discuss the sPHENIX detector and physics program which aims to bring full calorimetric based jet reconstruction to RHIC in order to explore the temperature dependence of the strongly interacting Quark Gluon Plasma.

Despite decades of high-energy nuclear physics experiments, relatively little is known about the structure of nuclei outside of the valence region. In order to explore this region, nuclear Deep Inelastic Collisions are required. The proposal to build an electron accelerator at RHIC (to form eRHIC) will be able to answer some of these outstanding questions. This paper will outline a couple of measurements that could be made at the new accelerator.

During the second long shutdown of the LHC in 2018, the ALICE Collaboration plans to install an upgrade of the ALICE Inner Tracking System (ITS) in the central barrel with seven layers of silicon detectors starting at 2.2 cm radial distance from the interaction region and a material budget as low as 0.3 % radiation length per layer. A single-hit resolution of 4 μm and a readout rate capability of up to 50 kHz in Pb–Pb collisions will allow new and unique measurements in the heavy-quark sector, i.e. charm and beauty. Using detailed Monte Carlo simulations of pp and Pb–Pb collisions we study the performance for heavy-flavor detection with an upgraded ITS in the following benchmark analyses: Charm meson and baryon production, i.e. D⁰ → K⁻π⁺ and Λ⁺_c → pK⁻p⁺, and beauty meson and baryon production, i.e. displaced vertices of B⁺ → ⁰π⁺ and Λ_b → Λ⁺_cπ⁻.

In these proceedings I describe how a future electron-ion collider will allow us to directly measure the initial spatial distribution of gluons in heavy ions, as well as its variance ("lumpiness") in exclusive diffraction. I show the feasibility of such a measurement by means of simulated data from the novel event generator Sartre.

The ALICE experiment is dedicated to the study of the quark gluon plasma in heavy-ion collisions at the CERN LHC. The Muon Forward Tracker (MFT) is under consideration by the ALICE experiment to be part of its program of detector upgrades to be installed during the LHC Long Shutdown 2 (LS2) planned for 2018. Designed as a silicon pixel detector added in the Muon Spectrometer acceptance (−4.0 < η < −2.5) upstream of the hadron absorber, the MFT will allow a drastic improvement of the measurements that are presently done with the Muon Spectrometer and, in addition, will give access to new measurements that are not possible with the present Muon Spectrometer setup. Motivations and preliminary results are discussed here, concerning the measurement of prompt and displaced charmonia, open heavy flavors, and low mass dimuons in central Pb–Pb collisions at = 5.5 TeV.

The production of strange and multi-strange hadrons in proton-proton (pp) and lead-lead (Pb-Pb) collisions is studied with the ALICE experiment at the CERN LHC. These particles are reconstructed via their weak decay topologies, exploiting the tracking and particle identification capabilities of ALICE. Measurements of central rapidity yields of Λ, Ξ⁻ and Ω⁻ baryons, their antiparticles and K⁰_S mesons are presented as a function of transverse momentum for Pb-Pb collisions at = 2.76 TeV. They are compared to those observed in pp collisions as well as to results from lower energy nucleus-nucleus measurements.

Measurements of the ratios of hadronic resonance yields to non-resonance yields can be used to study the properties of the hadronic phase of high-energy heavy-ion collisions. A change in resonance masses or widths could be an indication of chiral symmetry restoration. Measurements of resonances in proton-proton collisions provide an important baseline for measurements in heavy-ion collisions as well as data for tuning QCD-inspired particle production models. The ALICE collaboration has measured the K*(892)⁰ and ϕ(1020) resonances in Pb–Pb collisions at = 2.76 TeV and the K*(892)⁰, ϕ(1020), and Σ*(1385)^± resonances in pp collisions at = 7 TeV. These measurements – including transverse momentum spectra, ratios to non-resonances, masses, and widths – are discussed and compared to theoretical predictions.

Strangeness enhancement is one of the possible signatures of the Quark Gluon Plasma formation and can be accessed through the measurement of ϕ meson production with respect to ρ and ω mesons. Vector mesons can be detected through their decays into muon pairs with the ALICE muon spectrometer.

We present transverse momentum spectra of ϕ and ρ + ω mesons in the rapidity range 2.5 < y < 4 in p-p collisions at = 7 TeV, as well as the absolute production cross sections at = 7 TeV and at = 2.76 TeV. We also show the ϕ/(ρ + ω) ratio in Pb-Pb collisions at = 2.76 TeV.

Results from the ALICE experiment on coherent J/ψ photoproduction in ultra-peripheral Pb-Pb collisions at = 2.76 TeV are presented. The J/ψ → μ⁺μ⁻ channel has been used to measure the cross section in the rapidity interval −3.6 < y < −2.6. The photoproduction cross section has been compared to several theoretical models. The best agreement between data and theoretical predictions is found for models which include nuclear gluon shadowing.