Table of contents

The 7th edition of the Workshop for Young Scientists on the Physics of Ultra-relativistic Nucleus-Nucleus Collisions (Hot Quarks 2016) was held on South Padre Island, Texas, United States from September 12-17, 2016. Following the traditions of the conference, the meeting gathered almost 70 participants in the first years of their scientific careers. The present issue contains the proceedings of this workshop.

As in the past, the Hot Quarks workshop offered a unique atmosphere for lively discussions and interpretation of the current measurements from high-energy nuclear collisions. Dedicated time at the end of each session for questions, including anonymous questions from the "box", are crucial for this workshop. Recent results and upgrades at CERN's Large Hadron Collider (LHC) and Brookhaven's Relativistic Heavy Ion Collider (RHIC) were presented. Recent theoretical developments were also extensively discussed as well as the perspectives for future facilities such as the Facility for Antiproton and Ion Research (FAIR) at Darmstadt and the Electron-Ion Collider at Brookhaven. 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 2016 Conference, who supported the authors of this volume: European Laboratory for Particle Physics CERN (Switzerland), Cyclotron Institute at Texas A&M University (USA), ExtreMe Matter Institute EMMI (Germany), Helmholtz Association and GSI under grant VH-NG-822 (Germany), Helmholtz International Center for FAIR (Germany), National Science Foundation (USA), Netherlands Organization for Scientific Research (Netherlands), Nuclear Physics Institute of the CAS (Czech Republic), the Ministry of Education, Youth and Sport (Czech Republic) and 3 sponsors who wish to remain anonymous.

Javier López Albacete, Universidad de Granada (Spain)

Jana Bielcikova, Nuclear Physics Inst. of the Czech Academy of Sciences (Czech Republic)

Rainer J. Fries, Texas A&M University (USA)

Jiangyong Jia, Stony Brook University and Brookhaven National Laboratory (USA)

André Mischke, Utrecht University and Nikhef Amsterdam (The Netherlands)

Hannah Petersen, Goethe University, FIAS and GSI (Germany)

Lijuan Ruan, Brookhaven National Laboratory (USA)

Sevil Salur, Rutgers University, (USA)

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.

High energy collisions of heavy nuclei permit the study of nuclear matter at temperatures and energy densities so high that the fundamental theory for strong interactions, QCD, predicts a phase transition to a plasma of quarks and gluons. This matter, called a Quark Gluon Plasma (QGP), has been studied experimentally for the last decade and has been observed to be a strongly interacting liquid with a low viscosity. High energy partons created early in the collision interact with the QGP and provide unique probes of its properties. Hard partons fragment into collimated sprays of particles called jets and have been studied through measurements of single particles, correlations between particles, and measurements of fully reconstructed jets. These measurements demonstrate partonic energy loss in the QGP and constrain the QGP's properties. Measurements of the jet structure give insight into the mechanism of this energy loss. The information we have learned from studies of jets and challenges for the field will be reviewed.

In this proceedings I briefly review the recent progress achieved on the calculation of v_n at high p_T via the coupling of a jet energy loss model with full event-by-event viscous hydrodynamics. It is shown that this framework can simultaneously describe experimental data for R_AA, v₂, and v₃ at high p_T. High p_T v₂ is found to be approximately linearly correlated with the soft v₂ on an event-by-event basis, which opens up a new way to correlate soft and hard observables in heavy ion collisions.

We report the results of γ_dir- and π⁰–hadron azimuthal correlations as a measure of the away-side jet-like correlated yields in central Au+Au and p+p collisions at $\sqrt{{s}_{{NN}}}=200$ GeV in the STAR experiment. The charged-hadron per-trigger yields at mid-rapidity with respect to high-p_Tγ_dir and π⁰ in central Au+Au collisions are compared with p+p collisions. Within uncertainties, the same ${z}_{T}({p}_{T}^{\rm{assoc}}/{p}_{T}^{\rm{trig}})$ dependence of the suppression is observed for γ_dir- and π⁰- triggers. The results are compared with energy-loss model predictions. The γ − jet measurements can provide further understanding on the redistribution of in-medium energy loss. Ongoing γ − jet studies in the STAR experiment are also discussed.

Key features of jet-medium interactions in heavy-ion collisions are modifications to the jet structure. Recent results from experiments at the LHC and RHIC have motivated several theoretical calculations and Monte Carlo models towards predicting these observables simultaneously. In this proceedings, the recoil picture in JEWEL is summarized and two independent procedures through which background subtraction can be performed in JEWEL are introduced. Information of the medium recoil in JEWEL significantly improves its description of several jet shape measurements.

A hot medium with a high density of unscreened color charges is produced in relativistic heavy-ion collisions. Jets are produced at the early stages of these collisions and are known to become attenuated as they propagate through the hot matter. One manifestation of this energy loss is a lower yield of jets emerging from the medium than expected in the absence of medium effects. Another manifestation of the energy loss is the modification of the dijet balance and the modification of fragmentation functions. In these proceedings, the latest ATLAS results on single jet suppression, dijet suppression, and modification of the jet internal structure in Pb+Pb collisions are presented.

These proceedings discuss the sensitivity of the nuclear modification factor R_AA of fully reconstructed jets to cold nuclear matter effects. To test the parton energy loss interpretation of the observed R_AA of ∼0.3, obtained from reconstructed jets in Pb–Pb collisions at $\sqrt{{s}_{{\rm{NN}}}}$ = 2.76 TeV, we measured the inclusive jet production in minimum bias p–Pb collisions at $\sqrt{{s}_{{\rm{NN}}}}$ = 5.02 TeV for resolution parameters R=0.2 and 0.4. The reconstructed jets incorporate the neutral and charged energy component and cover a momentum range ${p}_{\rm{T}}^{{\rm{jet}}}$ = 20-90 GeV. The comparison of the jet yield to PYTHIA simulations shows no significant depletion in the measured jet cross section attributed to cold nuclear matter effects present in p–Pb collisions.

Measurements of dijet p_T correlations in both Pb+Pb and pp collisions at a nucleon–nucleon centre-of-mass energy of $\sqrt{{s}_{{\rm{NN}}}}$ = 2.76 TeV are presented. The measurements were performed with the ATLAS detector at the Large Hadron Collider (LHC) using Pb+Pb and pp data samples with integrated luminosities of 0.14 nb⁻¹ and 4.0 pb⁻¹, respectively. Jets were reconstructed using the anti-k_t algorithm with R = 0.4. A background subtraction procedure was applied to correct the jets for the large underlying event present in Pb+Pb collisions. The leading and subleading jet transverse momenta are denoted p_T1 and p_T2. An unfolding procedure is applied to the two-dimensional p_T1-p_T2 distributions to account for experimental effects in the measurement of both jets. Distributions of $\frac{1}{N}\frac{{\rm{d}}N}{{\rm{d}}{x}_{{\rm{J}}}}$, where ${x}_{{\rm{J}}}=\frac{{p}_{{{\rm{T}}}_{2}}}{{p}_{{{\rm{T}}}_{1}}}$, are presented as a function of p_T1 and collision centrality. The distributions are found to be similar in peripheral Pb+Pb collisions and pp collisions, but highly modified in central Pb+Pb collisions. The results are qualitatively consistent with expectations from partonic energy loss.

We present the configuration in which a quark-antiquark pair with a fixed opening angle emits a hard gluon inside a medium, and an additional very soft emission afterwards (double antenna). We discuss the coherence effects in terms of the survival probability, which describes the interaction of the q$\bar{q}$g system with the medium. We generalize previous studies of the antenna radiation to the case of more than two emitters and prove that this generalization provides further support to the picture of jet quenching with effective emitters in the parton cascade.

The observed suppression of particle production at high transverse momentum in nucleus-nucleus collisions at high energies is an effect of the energy loss of partons as they propagate through the hot and dense deconfined QCD medium. The measurement of transverse momentum spectra of primary charged particles in Pb–Pb collisions and the comparison to the measurement in pp collisions are important to study the properties of the deconfined medium. In 2015, pp and Pb–Pb collisions have been recorded at the LHC at the energy of $\sqrt{{s}_{NN}}$ = 5.02 TeV. The inclusive charged particle production is measured with the ALICE detector in the pseudo-rapidity range |η| < 0.8 and in the transverse momentum range 0.15 < p_T < 40 GeV/c. The spectra in Pb–Pb, determined for several centrality intervals, are compared to the reference spectrum in pp collisions by calculating the nuclear modification factor R_AA. The data are compared to measurements at the lower collision energy of 2.76 TeV and to model predictions.

Jet quenching is observed at both RHIC and LHC energies. This suggests that partons lose energy as they traverse the medium. When the trigger jet is studied relative to the event plane, the path length dependence of medium modifications can be studied. We present measurements of the angular correlations relative to the event plane between reconstructed jets and charged hadrons in Pb–Pb collisions at $\sqrt{{s}_{{NN}}}$ = 2.76 TeV in ALICE. A newly implemented, robust background subtraction method to remove the complex, flow dominated, combinatorial background is used in this analysis.

The ALICE experiment at the LHC is optimized to study the quark-gluon plasma (QGP), created in heavy-ion collisions. The medium-induced energy loss of particles can be investigated via the measurement of neutral meson spectra in heavy-ion collisions as well as via neutral meson-hadron correlations. Neutral mesons are identified from decay photon pairs via the invariant mass technique. Photons are measured in ALICE directly in the two electromagnetic calorimeters (PHOS and EMCal), as well as via the method of photon conversion (PCM) into electron-positon pairs, where the latter are measured in the inner tracking system (ITS) and the time projection chamber (TPC). Results obtained from EMCal, PHOS and PCM are consistent and allow measurements of spectra with high precision over a wide kinematical range. Suppression of the high-p_T meson production is observed through the mesasurement of nuclear modification factor (R_AA), which decreases with increasing the centrality of the collision. The suppression of the per-trigger yield on the away side in high-p_Tπ⁰ hadron correlations as measured by the modification factor (I_AA) also shows evidence for parton energy loss in the medium.

sPHENIX is a new collaboration and future detector project at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC). It seeks to answer fundamental questions on the nature of the quark gluon plasma (QGP), including its coupling strength and temperature dependence, by using a suite of precision jet and upsilon measurements that probe different length scales of the QGP. This is possible with a full acceptance, |η| < 1 and 0-2π in φ, electromagentic and hadronic calorimeters and precision tracking enabled by a 1.5 T superconducting magnet. With the increased luminosity afforded by accelerator upgrades, sPHENIX is going to perform high statistics measurements extending the kinematic reach at RHIC to overlap the LHC's. This overlap is going to facilitate a better understanding of the role of temperature, density and parton virtuality in QGP dynamics and, specifically, jet quenching. This paper focuses on key future measurements and the current state of the sPHENIX project.

The final day of the Hot Quarks 2016 conference was focused on the discussions of the initial stages of colliding nuclei and hadrons. In this conference proceedings we give a brief overview of a few selective topics discussed at the conference that include latest developments in the theoretical description of the initial state towards understanding a number of recent experimental results from RHIC and LHC.

Bose-Einstein correlations between identified charged pions are measured for p+Pb collisions at $\sqrt{{s}_{{\rm{NN}}}}$ = 5.02 TeV with the ATLAS detector using a total integrated luminosity of 28 nb⁻¹. Pions are identified using ionisation energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of average transverse pair momentum (k_T) and rapidity (${y}_{\pi \pi }^{* }$) as well as collision centrality. Pairs are selected with a rapidity −2 < ${y}_{\pi \pi }^{* }$ < 1 and with an average transverse momentum 0.1 < k_T < 0.8 GeV. The effect on the two-particle correlation function from jet fragmentation is studied, and a new method for constraining its contributions to the measured correlations is described. The measured source sizes are substantially larger in more central collisions and are observed to decrease with increasing pair k_T. A correlation with the local single-particle multiplicity dN_ch/dy* is demonstrated. The scaling of the extracted radii with the mean number of participants is also used to compare a selection of initial-geometry models. The cross term R_ol, which couples radial and longitudinal expansion, is measured as a function of rapidity, and a departure from zero is observed with 4.8 σ combined significance for ${y}_{\pi \pi }^{* }$ > −1 in the most central events.

The ALICE detector has excellent Particle IDentification (PID) capabilities in the central barrel (|η| < 0.9). This allows identified hadron production to be measured over a wide transverse momentum (p_T) range, using different sub-detectors and techniques: their specific energy loss (dE/dx), the velocity determination via time-of-flight measurement, the Cherenkov angle or their characteristic weak decay topology. Results on identified light flavour hadron production at mid-rapidity measured by ALICE in proton-proton collisions at $\sqrt{s}$ = 13 TeV are presented and compared with previous measurements performed at lower energies. The results cover a wide range of particle species including long-lived hadrons, resonances and multi-strange baryons over the p_T range from 150 MeV/c up to 20 GeV/c, depending on the particle species.

We use leading order effective kinetic theory to simulate the pre-equilibrium evolution of transverse energy and flow perturbations in heavy-ion collisions. We provide a Green function which propagates the initial perturbations of the energy-momentum tensor to a time when hydrodynamics becomes applicable. With this map, the pre-thermal evolution from saturated nuclei to hydrodynamics can be modeled in the framework of weakly coupled QCD.

Drell-Yan pair production off nuclei is an ideal tool to test the cold nuclear effects occurring before a hard collision since no interaction in the final state is expected, neither energy loss or absorption. We present for the first time a comprehensive study of the nucleus-to-nucleon production ratio (the nuclear modification factor) within the color dipole approach using the Green function formalism which naturally incorporates for the color transparency and quantum coherence effects. We study a different onset of nuclear shadowing in various kinematical regions. At large values of the Feynman variable x_F and dilepton invariant mass M we include also a suppression factor due to restrictions caused by the energy conservation induced by multiple initial state interactions (ISI effects). We present a variety of predictions for the nuclear suppression as a function of x_F and M that can be verified by experiments at RHIC and LHC. The mixing of coherence effects with ISI effects can be eliminated going to large values of the dilepton invariant mass. Then predictions for the nuclear suppression is a direct manifestation for the onset of net ISI effects that can be verified by the future measurements.

The early time dynamics of heavy ion collisions can be described by classical fields in an approximation of Quantum ChromoDynamics (QCD) called Color Glass Condensate (CGC). Monte-Carlo sampling of the color charge for the incoming nuclei are used to calculate their classical gluon fields. Following the recent work by Chen et al. we calculate the energy momentum tensor of those fields at early times in the collision event-by-event. This can then be used for subsequent hydrodynamic evolution of the single events.

The large statistics of data collected at the high energies reached at the Large Hadron Collider have provided unprecedented opportunities to probe in more detail the mechanisms of particle production in small collision systems such as proton–proton (pp) and proton–lead (p–Pb) collisions. It is particularly interesting to perform such studies in high-multiplicity events, where, in the last years, features where found that are reminiscent of phenomena interpreted as signs of collective behaviour in lead–lead (Pb–Pb) collisions. These observations justify a comprehensive study of the production of identified particles to further investigate the dynamics in small collision systems. The ALICE detector, thanks to its excellent particle identification capabilities, allows the measurement of identified particles over a wide range of transverse momentum (p_T). In these proceedings we report on the p_T distributions of π, K, p, ${K}_{S}^{0}$, K^*, Λ, Ξ and Ω measured as function of the charged-particle multiplicity density in pp collisions at $\sqrt{s}$ = 7 TeV. We further report on the study of particle ratios in comparison to Monte Carlo models and in different collision systems. In particular, the production of hadrons containing strange quarks is also discussed as a function of the event multiplicity.

Hadrons containing heavy-flavors are unique probes of the properties of the hot and dense QCD medium produced in heavy-ion collisions. Due to their large masses, heavy quarks are produced at the initial stage of the collision, almost exclusively via hard partonic scattering processes. Therefore, they are expected to experience the full collision history propagating through and interacting with the QCD medium. The parton energy loss, which is sensitive to the transport coefficients of the produced medium, can be studied experimentally by measuring the nuclear modification factor which accounts for the modification of the heavy–flavored hadron yield in Pb–Pb collisions with respect to pp collisions. In semi-central Pb–Pb collisions, the degree of thermalization of charm quarks in the QCD medium can be accessed via the measurement of the heavy flavor elliptic flow v₂ at low pT. Furthermore, the measurement of heavy-flavors production in pp collisions allows testing the perturbative QCD calculations. The PHENIX and STAR Collaborations at the Relativistic Heavy-Ion Collider and ALICE, CMS and ATLAS Collaborations at the Large Hadron Collider have measured the production of charmonium and bottonium states as well as open heavy flavor hadrons via their hadronic and semi-leptonic decays at mid-rapidity and in the semi-muonic decay channel at forward rapidity in pp, p-A and A–A collisions in an energy domain that ranges from $\sqrt{s}$ = 0.2 TeV to $\sqrt{s}$ = 13 TeV in pp collisions and from $\sqrt{{s}_{{\rm{NN}}}}$ = 0.2 TeV to $\sqrt{{s}_{{\rm{NN}}}}$ = 5.02 TeV in A–A collisions. In this contribution the latest experimental results will be reviewed.

The study of J/ψ azimuthal anisotropy allows for a disentanglement of various production mechanisms and possibly an access to charm quark azimuthal anisotropy. J/ψ meson produced from direct pQCD processes have little azimuthal anisotropy due to the lack of collectivity or azimuthal preference of initial emitting, while J/ψ meson produced from recombination of charm quarks in the medium are expected to inherit the azimuthal anisotropy of the constituent charm quarks. We present measurements of J/ψ azimuthal anisotropy, with J/ψ reconstructed via the di-electron channel, as a function of transverse momentum in Au+Au collisions at $\sqrt{{s}_{NN}}=200\,\mathrm{GeV}$. This analysis is carried out with data taken by the STAR experiment during RHIC operation in year 2011. Combined with the published results using 2010 data, the updated results provide further support to the conclusion that J/ψ production above 2 GeV/c is unlikely to be dominated by regeneration of fully thermalized charm quarks.

We discuss the propagation of heavy quarks (charm and bottom) through the QGP by means of a relativistic Boltzmann transport approach including both collisional and radiative energy loss mechanisms. In particular we investigate the impact of induced gluon radiation by dynamical QCD medium implementing in our transport model a formula for the emitted gluon spectrum calculated in a higher-twist scheme. We notice that in the region of high transverse momentum (p_T > 10 GeV) radiative processes play an essential role giving a dominant contribution to the generation of R_AA and v₂ at momentum values for which the energy loss by collisions is in the perturbative regime.

An overview of recent D⁺, D⁰, D^*+ and ${{\rm{D}}}_{{\rm{s}}}^{+}$ measurements performed by ALICE at central rapidity in proton-proton collisions at $\sqrt{s}=7$ and 8 TeV, as well as lead-lead collisions at $\sqrt{{s}_{NN}}=2.76\,{\rm{TeV}}$, is presented. An emphasis is put on the discussion of theoretical predictions with respect to the LHC Run I data.

Measurements of heavy (charm and beauty) quarks provide useful insights into the properties of the quark–gluon plasma. The good particle identification capabilities of ALICE make a measurement based on the electrons from semi-leptonic decays of heavy-flavour hadrons feasible. This approach makes use of the large branching ratios (≈ 10 − 20%) of heavy–flavour hadrons into electrons. Separation of the contribution from beauty-hadron decay electrons was achieved by utilizing the large decay length of the associated hadrons, making the investigation of beauty quarks in the medium possible. By comparing measurements in p–Pb and Pb–Pb collisions, it is possible to disentangle effects of cold nuclear matter from those of the hot and dense medium. The results show a strong change in the transverse momentum distribution of electrons from beauty-hadron decays in central Pb–Pb collisions with respect to the proton–proton case. No significant change from proton–proton collisions can be seen in the p–Pb case, suggesting that the modification is a final state effect.

We report on the latest measurements of the production of ϒ mesons in heavy-ion collisions from the STAR experiment at RHIC. New measurements of the nuclear modification factors of the ϒ(1S+2S+3S) and ϒ(1S) states in U+U collisions at $\sqrt{{s}_{{\rm{N}}{\rm{N}}}}=193\,\mathrm{GeV}$ are presented as a function of the number of participants (N_part) in the collisions. In addition, the suppression of ϒ(1S) and ϒ(2S+2S) is presented versus the quark-antiquark binding energy. Preliminary results on ϒ suppression in Au+Au collisions at $\sqrt{{s}_{{\rm{N}}{\rm{N}}}}=200\,\mathrm{GeV}$, reconstructed via the dimuon channel, are also reported.

In this paper, we present measurements of J/ψ cross-section and yield dependence on charged-particle multiplicity in p+p collisions at $\sqrt{s}=500\,{\rm{GeV}}$ at mid-rapidity in the transverse momentum range of 0-20 GeV/c. Measurements of J/ψ nuclear modification factors in Au+Au collisions at $\sqrt{{s}_{NN}}=200\,{\rm{GeV}}$ up to 14 GeV/c via the di-muon channel with the full data sample taken during RHIC 2014 run is also presented.

We report on the results of the charmonium production in Pb-Pb collisions at $\sqrt{{s}_{{\rm{NN}}}}=2.76$ and 5.02 TeV measured with the ALICE detector at the LHC. In particular, we focus on the new measurements obtained at $\sqrt{{s}_{{\rm{N}}{\rm{N}}}}=5.02\,{\rm{TeV}}$ for the J/ψ at forward rapidity in the dimuon decay channel and their comparison with previous measurements at lower energy and model calculations.

Because of their large masses, charm quarks are predominantly produced in the early stages of the heavy-ion collisions via hard scatterings. Therefore, they experience the entire evolution of the Quark-Gluon Plasma created in such collisions. Compared to light quarks, charm quarks thermalize more slowly. Therefore, the open charm hadrons present a unique probe to the properties of the hot and dense nuclear matter by measuring their energy loss and degree of thermalization in the medium. Furthermore, with the combined measurements of D⁰ and D_s mesons, we can study multiple modes of coalescence of charm quarks with light quarks in heavy-ion collisions. Heavy Flavor Tracker at the STAR experiment enables full topological reconstruction of open charm hadrons which greatly improves measurements of D⁰ mesons and opens the door to reconstructing the D_s mesons for the first time at RHIC. In this paper, we present the nuclear modification factor and azimuthal anisotropy for the D⁰ and D_s mesons as well as the ratio of D_s/D⁰ in Au+Au collisions at the center-of-mass energy $\sqrt{{s}_{{\rm{N}}{\rm{N}}}}=200\,\mathrm{GeV}$.

An overview of ALICE results on the measurement of J/ψ production in pp collisions at $\sqrt{s}=7\,\mathrm{TeV}$ collected during the LHC Run-1 period is presented, as well as first results at forward rapidity from pp collisions at $\,\sqrt{s}=13\,\mathrm{TeV}$ collected during the LHC Run-2 period. In particular, the measurement of J/ψ production as a function of transverse momentum and charged-particle multiplicity are discussed and compared to theoretical model calculations.

We present the current status of the measurement of jets that contain a D meson (D-tagged jets) with the ALICE detector. D⁰-meson candidates, identified via their hadronic decay into a Kπ pair, were combined with the other charged tracks reconstructed with the central tracking system, using the anti-k_T jet-finding algorithm. The yield of D-tagged jets was extracted through an invariant mass analysis of the D-meson candidates. A Monte Carlo simulation was used to determine the detector performance and validate the signal extraction techniques.

The LHC Run 1 results of the analysis of charmonium production in pp, pPb and PbPb collisions with the CMS experiment are reported. The coherent J/ψ photoproduction cross section is measured as a function of rapidity in ultra-peripheral PbPb collisions at 2.76 TeV. The forward-backward ratio of prompt J/ψ yields in pPb collisions at 5.02 TeV is presented as a function of the event activity and p_T. The nuclear modification factor of prompt J/ψ in PbPb collisions at 2.76 TeV is shown as a function of rapidity, centrality and p_T. Finally, the ratio of ψ(2S) to J/ψ yields in PbPb collisions with respect to pp collisions at 2.76 TeV is analysed in different rapidity and centrality bins.

In these proceedings, we will present the new results of the Non-Photonic Electron (NPE) production from semi-leptonic decays of open heavy flavor hadrons at the STAR experiment. Firstly we will report the updated results on NPE production in p+p collisions at $\sqrt{s}=200\,{\rm{GeV}}$ with much improved precision and wider kinematic coverage than previous measurements. Secondly we will report measurements of the nuclear modification factor, R_AA, for NPE production in Au+Au collisions at $\sqrt{{s}_{{\rm{NN}}}}=200\,{\rm{GeV}}$ with this new p+p reference. The NPE R_AA shows large suppression at high transverse momenta (p_T) in central collisions, which reduces gradually towards more peripheral collisions, and an enhancement at low p_T with large systematic uncertainties from the p+p reference. We will compare NPE R_AA to the R_AA of charm decayed electrons, D⁰ mesons and light hadrons in Au+Au collisions as well as to NPE and D⁰ mesons in central U+U collisions and show that they are all consistent within the uncertainties. Finally we will report the results on measurements of NPE from open bottom hadron decays and discuss the prospect of measuring NPE from open bottom and charm hadron decays separately utilizing the Heavy Flavor Tracker.

Heavy flavours (charm and beauty) and electroweak bosons (W and Z) are produced in initial hard partonic scatterings. The former interact strongly with the medium formed in ultra-relativistic heavy-ion collisions throughout its evolution, thus making them well suited to investigate its properties. Furthermore, heavy-flavour measurements in proton-nucleus collisions can be used to investigate initial-state effects whereas in proton-proton (pp) collisions they are considered an important test for perturbative Quantum ChromoDynamics (pQCD) predictions. In addition, open heavy-flavour measurements in pp collisions are used as a reference for proton-lead (p–Pb) and lead-lead (Pb–Pb) collisions. On the other hand, electroweak bosons and their leptonic decay products only interact weakly with the QCD matter and thus are suitable probes to test the validity of binary-collision scaling of hard processes. Moreover, their measurements in p–Pb collisions could help to constrain nuclear parton distribution functions. The ALICE muon spectrometer allows the measurement of open heavy flavour, W- and Z-boson production at forward rapidity (−4.0 < η < −2.5) exploiting their (di)muonic decay channel. In this talk the results obtained with the LHC Run I data in pp, p–Pb and Pb–Pb collisions will be discussed and compared with theoretical predictions.

The quark degrees of freedom of the QGP with special focus on mass effects are investigated. A next-to-leading-order perturbation theory approach with quark mass dependence is applied and compared to lattice QCD results.

An introductory overview of electromagnetic probe production in ultra-relativistic heavy ion collisions is provided. Experimental evidence supporting the production of thermal photons and dileptons in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) are reviewed. Thermal electromagnetic probe production from hydrodynamical models of collisions is discussed.

The production of low-mass dielectrons is measured with ALICE at the LHC in pp, p-Pb and Pb–Pb collisions. The dielectron yield in p-Pb collisions in comparison to the expected hadronic cocktail shows an overall reasonable agreement. The production of direct virtual photons, visible as an excess over the hadronic cocktail, in Pb–Pb collisions is measured in two transverse momentum ranges. A feasibility study for the future LHC Run 3 indicates that it should be possible to extract an effective temperature with a combined statistical and systematic uncertainty of around 30%.

In this work the non-equilibrium dilepton production from a hadronic transport approach (SMASH) is presented. The dilepton emission from the hadronic stage is of interest for current HADES results measured at GSI in the beam energy range from 1.25 - 3.5 GeV. Also at high collision energies (RHIC/LHC) the later dilute stages of the reaction are dominated by hadronic dynamics. The newly developed hadronic transport approach called SMASH (=Simulating Many Accelerated Strongly-interacting Hadrons) is introduced first. After explaining the basic interaction mechanisms, a comparison of elementary cross sections for pion production to experimental data is shown. The dilepton production within SMASH is explained in detail. The main contribution to the dilepton spectra in the low energy regime of GSI/FAIR/RHIC-BES originates from resonance decays. Results of the dilepton production with SMASH such as invariant mass spectra are shown.

In this study we discuss our results on the spectrum of photons emitted from the quark-gluon plasma produced in heavy ion collisions at RHIC energies. Simulating the space-time evolution of the fireball by solving the relativistic Boltzmann transport equation and including two-particle scattering processes with photon emission allows us to make a first step in the description of thermal photons from the QGP as well as of those produced in the pre-equilibrium stage. Indeed, we consider not only a standard Glauber initial condition but also a model in which quarks and gluons are produced in the very early stage through the Schwinger mechanism by the decay of an initial color-electric field. In the latter approach relativistic kinetic equations are coupled in a self-consistent way to field equations. We aim at spotting the impact of early stage non-equilibrium dynamics on the photon production.

The nuclear phase diagram is mapped using beam energy scans of relativistic heavy-ion collisions. This mapping is possible because different collision energies develop along different trajectories through the phase diagram. High energy collisions will evolve though a crossover phase transition according to lattice QCD, but lower collision energies may traverse a first order phase transition. There are hints for this first order phase transition and its critical endpoint, but further measurements and theoretical guidance is needed. In addition to mapping the phase transition, beam energy scans allow us to see if we can turn off the signatures of deconfinement. If an observable is a real signature for the formation of the deconfined state called quark-gluon plasma, then it should turn off at sufficiently low collision energies. In this summary talk I will show the current state of the field using beam energy scan results from RHIC and SPS, I will show where precise theoretical guidance is needed for understanding recent measurements, and I will motivate the need for more data and new measurements from FAIR, NICA, RHIC, and the SPS.

The understanding of the phase structure and the fundamental properties of QCD matter from its microscopic description requires appropriate first-principle approaches. Here I review the progress towards a quantitative first-principle continuum approach within the framework of the Functional Renormalization group established by the fQCD collaboration. I focus on recent quantitative results for quenched QCD and Yang-Mills in the vacuum before addressing the calculation of dynamical quantities such as spectral functions and transport coefficients in this framework.

Currently at the Beam Energy Scan at RHIC experimental efforts are being made to find the QCD critical point. On the theoretical side, the behavior of higher-order susceptibilities of the net-baryon charge from Lattice QCD at µ_B = 0 may allow us to estimate the position of the critical point in the QCD phase diagram. However, even if the series expansion continues to higher-orders, there is always the possibility to miss the critical point behavior due to truncation errors. An alternative approach is to use a black hole engineered holographic model, which displays a critical point at large densities and matches lattice susceptibilities at µB = 0. Using the thermodynamic data from this black hole model, we obtain the freeze-out points extracted from the net-protons distribution measured at STAR and explore higher order fluctuations at the lowest energies at the beam energy scan to investigate signatures of the critical point.

We report our recent study of the effect of the magnetic field on the elliptic flows of quarks and antiquarks in relativistic heavy ion collisions using the anomalous transport model. We have found that the magnetic field can lead to a charge quadrupole moment in the transverse plane of a heavy ion collisions if the magnetic field lasts sufficiently long and the charge asymmetry of produced matter is nonzero. As the matter expands, the charge quadrupole moment leads to a splitting between the elliptic flows of quarks and antiquarks. However, the elliptic flow difference increases with the charge asymmetry, which is expected from the chiral magnetic wave formed in the quark-gluon plasma, only if the Lorentz force is neglected and the quark-antiquark scattering is dominated by the chirality changing channel.

We show that measurements of the rapidity dependence of transverse momentum correlations can be used to determine the characteristic time τ_π that dictates the rate of isotropization of the stress energy tensor, as well as the shear viscosity ν = η/sT. We formulate methods for computing these correlations using second order dissipative hydrodynamics with noise. Current data are consistent with τ_π/ν ∼ 10 but targeted measurements can improve this precision.

We report measurements of two-particle charge-dependent correlations in pp, p-Pb, and Pb-Pb collisions at $\sqrt{{s}_{{\rm{N}}{\rm{N}}}}=\mathrm{7,\; 5.02}$, and 2.76 TeV, respectively, as a function of pseudorapidity and azimuthal angle differences. These measurements, carried out using the balance function, probe the charge creation time and the development of collectivity in the produced systems. The balance function is studied as a function of the event multiplicity as well as the transverse momentum (p_T) of charged particles detected in the range |η| < 0.8. In the low transverse momentum region, 0.2 < p_T < 2.0 GeV/c, the balance function becomes narrower in both Δη and Δφ directions in all three systems for events with higher multiplicity. For higher values of transverse momenta, the balance function becomes even narrower but exhibits no significant multiplicity dependence, indicating that the observed narrowing with increasing multiplicity at low p_T is a feature of bulk particle production.

The spinodal instabilities of both confined and expanding baryon-rich quark matters are studied in a transport model derived from the Nambu-Jona-Lasino model. Appreciable higher-order density moments are seen as a result of the first-order phase transition in both cases. The skewness of the quark number event-by-event distribution in a small subvolume of the system becomes appreciable for the confined quark matter. For the expanding quark matter, the density fluctuations lead to enhanced anisotropic flows and dilepton yield.

Event-by-event relativistic hydrodynamics has been extremely successful in describing flow observables in heavy-ion collisions. However, the initial state and viscosity simultaneously affect comparisons to data so a discussion of experimental observables that help to distinguish the two follows. Specific problems that arise in the hydrodynamical modeling at the Beam Energy Scan are also addressed.

This manuscript reviews recent theoretical progress on the understanding of the quark gluon plasma in a magnetic field that I presented on the conference Hot Quarks 2016, held at South Padre Island, Texas, USA, 12-17 September 2016. It is shown that, using a holographic bottom-up Einstein-Maxwell-Dilaton model, one can have a good quantitative agreement with Lattice result for QCD equation of state and Polyakov loop with nonzero magnetic field. I also present results for the anisotropic shear viscosity ratio η_||/η_⊥, with the conclusion that η_|| < η_⊥ for non-zero magnetic field.

This is a contribution for the Proceedings of the Conference Hot Quarks 2016, held at South Padre Island, Texas, USA, 12-17 September 2016. I briefly review some thermodynamic and baryon transport results obtained from a bottom-up Einstein-Maxwell-Dilaton holographic model engineered to describe the physics of the quark-gluon plasma at finite temperature and baryon density. The results for the equation of state, baryon susceptibilities, and the curvature of the crossover band are in quantitative agreement with the corresponding lattice QCD results with 2 + 1 flavors and physical quark masses. Baryon diffusion is predicted to be suppressed by increasing the baryon chemical potential.

The ALICE experiment is designed and optimised to study the properties of the Quark-Gluon Plasma (QGP), a new state of matter, which is expected to be created at the high energy densities reached at the LHC. One of the key observables used to characterise the transport properties and the equation of state of the QGP is the azimuthal anisotropy in particle production, which is usually called anisotropic flow. In this presentation, we report the first measurements of anisotropic flow in Pb–Pb collisions at $\sqrt{{s}_{{\rm{N}}{\rm{N}}}}={\rm{5.02\; TeV}}$, the highest energy ever achieved in heavy–ion collisions, and compare them with both theoretical predictions and experimental measurements at lower energies. This provides a unique opportunity to test the validity of the hydrodynamic paradigm at new energies and to further constrain key transport parameters of the QGP, such as the shear viscosity over entropy ratio.

We show that a transient effective theory for rapid anisotropically expanding systems based on the Boltzmann equation exhibits transient oscillatory behavior.

We study an azimuthally-symmetric boost-invariant quark-gluon plasma using quasiparticle anisotropic hydrodynamics including the effects of both shear and bulk viscosities. We compare results obtained using the quasiparticle method with the standard anisotropic hydrodynamics and viscous hydrodynamics. We consider the predictions of the three methods for the differential particle spectra and mean transverse momentum. We find that the three methods agree for small shear viscosity to entropy density ratio, η/s, but show differences at large η/s. Additionally, we find that the standard anisotropic hydrodynamics method shows suppressed production at low transverse-momentum compared to the other two methods, and the bulk-viscous correction can drive the primordial particle spectra negative at large p_T in viscous hydrodynamics.

Present hydrodynamics-based simulations of heavy-ion collisions neglect the feedback from the frozen-out particles flying back into the hydrodynamical region. This causes an artefact called "negative Cooper-Frye contributions", which is negligible for high collision energies, but becomes significant for lower RHIC BES energies and for event-by-event simulations. To avoid negative Cooper-Frye contributions, while still preserving hydrodynamical behavior, we propose a pure hadronic transport approach with forced thermalization in the regions of high energy density. It is demonstrated that this approach exhibits enhancement of strangeness and mean transverse momenta compared to conventional transport – an effect typical for hydrodynamical approaches.

The transition from a hydrodynamical modeling to a particle-based approach is a crucial element of the description of high-energy heavy-ion collisions. Assuming this "freeze out" happens instantaneously at each point of the expanding medium, we show that the local phase-space distribution of the emitted particles is asymmetric in momentum space. This suggests the use of anisotropic hydrodynamics for the last stages of the fluid evolution. We discuss how observables depend on the amount of momentum-space anisotropy at freeze out and how smaller or larger anisotropies allow for different values of the freeze-out temperature.

We make phenomenological predictions for particle spectra and elliptic flow in heavy-ion collisions using 3+1d anisotropic hydrodynamics (aHydro) including the effects of both shear and bulk viscosities. The dynamical equations necessary are derived by taking moments of the Boltzmann equation allowing for three distinct (diagonal) momentum-space anisotropy parameters. The formulation is based on relaxation-time approximation for the collisional kernel and a lattice-QCD-based equation of state. Evolving the system to late times, we calculate particle production using THERMINATOR 2, modified to account for an ellipsoidal distribution function. We obtain particle spectra for different particle species such as pions, kaons, and protons, and elliptic flow v₂ as a function of centrality, transverse momentum, and rapidity. In our model, we have four free parameters, i.e. freeze-out temperature, initial central energy density, initial momentum-space anisotropies, and shear viscosity to entropy density ratio. Using a multidimensional fit to LHC experimental data, we make a preliminary extraction of these parameters. We find reasonable agreement between 3+1d aHydro and available experimental data for η/s ∼ 0:23.

The azimuthal anisotropy of particle emission is a good observable to study the property of the quark gluon plasma (QGP), from the point of view of not only its collective dynamics but also the energy loss of hard scattered partons in it. We measured charged hadron v₂ as a function of p_T in 0.5 < p_T < 10 GeV/c for minimum bias and several centrality Au+Au collisions at $\sqrt{{s}_{NN}}={\rm{200\; GeV}}$ using the RHIC Year-2014 data, which significantly improved the statistical precision compared to the previous results. It was found that the v₂'s for charged hadrons are consistently above zero up to p_T = 10 GeV/c over the centralities. It was also found that there is a difference in v₂ between charged hadrons and neutral pions for p_T <7 GeV/c.

Hadronic observables in the final stage of heavy ion collision can be described well by fluid dynamics or blast wave parameterizations. We improve existing blast wave models by adding shear viscous corrections to the particle distributions in the Navier-Stokes approximation. The specific shear viscosity η/s of a hadron gas at the freeze-out temperature is a new parameter in this model. We extract the blast wave parameters with viscous corrections from experimental data which leads to constraints on the specific shear viscosity at kinetic freeze-out. Preliminary results show η/s is rather small.

The determination of transport coefficients plays a central role in characterizing hot and dense nuclear matter. In the present work we calculate the electric conductivity of hot hadronic matter by extracting it from the ρ meson spectral function, as its zero-energy limit at vanishing momentum. Using hadronic many-body theory, we calculate the ρ meson self-energy in a pion gas. This requires the dressing of the pion propagators in the ρ self-energy with π-ρ loops, and the inclusion of vertex corrections to maintain gauge invariance. The resulting spectral function is used to calculate the electric conductivity of hot hadronic matter. In particular, we analyze the transport peak of the spectral function and extract its behavior with temperature and coupling strength. Our results suggest that, while obeying lower bounds proposed by conformal field theories in the strong-coupling limit, hot pion matter is a strongly-coupled medium.

Heavy ion collisions at extremely high energy, such as the top energy at RHIC, exhibit the property of transparency where there is a clear separation between the almost net-baryon-free central rapidity region and the net-baryon-rich fragmentation region. We calculate the net-baryon rapidity loss and the nuclear excitation energy using the energy-momentum tensor obtained from the McLerran-Venugopalan model. Nuclear compression during the collision is further estimated using a simple space-time picture. The results show that extremely high baryon densities, about twenty times larger than the normal nuclear density, can be achieved in the fragmentation regions.

The properties of the quark-gluon plasma have been extensively studied in high-energy nuclear collisions at RHIC. Femtoscopic measurements of two-particle correlations at small relative momenta reveal the space-time characteristics of the system at the moment of particle emission. In comparison to analyses using the most abundant pions, like-sign kaons provide a cleaner probe of the emission source as they less frequently result from resonance weak decays. Additionally, kaons contain strange quarks so these measurements can be sensitive to different effects and earlier collision stages. Pairs of like-sign kaons exhibit correlations due to Coulomb interactions and Bose-Einstein quantum statistics. The system of unlike-sign kaons contains a narrow φ(1020) resonance in the final state. Femtoscopic measurements have been predicted to be particularly sensitive to the source size and momentum-space correlations in the region of this resonance.

In this proceedings, we present the STAR preliminary results on the like-sign and unlike-sign kaon femtoscopic correlation functions in 200 GeV Au+Au collisions at RHIC. Collision centrality and the transverse pair momentum k_T dependence of the radius parameters will be discussed. The results from unlike-sign kaon correlation functions will be compared with model predictions [1].

In order to study the hot hadronic matter created in heavy-ion collisions, it is important to compare particle production in large systems to that in smaller systems, such as proton-proton (pp) and proton-lead (p–Pb) collisions. In particular, resonances with different lifetimes are good candidates to probe the interplay of particle re-scattering and regeneration in the hadronic phase. The yields of the strange and double-strange hyperon resonances Σ(1385)^± and Ξ(1530)⁰ are measured in the rapidity range −0.5 < y_CMS < 0 in p–Pb collisions at $\sqrt{{s}_{{\rm{N}}{\rm{N}}}}={\rm{5.02\; TeV}}$ with the ALICE detector at the LHC. We report on the transverse momentum distributions and mean transverse momentum as a function of the charged-particle multiplicity. These results complement the information derived from the measurements of other resonances such as K*(892)⁰ and ˚(1020). The multiplicity dependence of the integrated yield ratios of excited hyperons to longer-lived particles is discussed and compared to model predictions from pQCD-inspired models such as PYTHIA8 as well as statistical hadronization models.

The high collision energies reached at the LHC open the possibility to study extensively the production of light (anti-)(hyper-)nuclei and exotic bound states in proton-proton (pp), proton-lead (p-Pb) and lead-lead (Pb-Pb) collisions.

ALICE has excellent particle identification (PID) capability which allows the detection of these rarely produced particles. PID is perfomed using several techniques, namely by exploiting the measurement of the specific ionization energy loss in the Time Projection Chamber (TPC) and the information of the Time-Of-Flight (TOF) detector.

The transverse momentum spectra and the yields (dN/dy) of light nuclei and anti-nuclei were obtained and results are discussed here, and the first measurement of deuteron elliptic flow is presented. Furthermore, the study of the production of (anti-)hypertriton and the status of the searches for exotic bound states, i.e. Λ-Λ and Λ-n, are discussed.

Results are compared to predictions from thermal and coalescence models in order to enquire into the production mechanisms of nuclei, hypernuclei and exotic bound states.

Heavier resonances are continually being added to the hadronic spectrum from the Particle Data Group that follow an exponentially increasing mass spectrum. However, it has been suggested that even further states predicted from Quark Models are needed in the hadronic spectrum in order to improve the agreement between the hadron resonance gas model predictions and lattice QCD data. We find that the inclusion of such states with extrapolated branching ratios slightly decreases the freezeout temperature. To eliminate ambiguities, we introduce a first principle method to extract the freeze-out temperature for charged kaons from experimental data, which yields a lower bound of T_fo ≳ 145 MeV for the highest collision energy at RHIC.