### Conveners

#### Section D

- Edmond Iancu (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))

#### Section D

- Piotr Bozek (AGH University of Science and Technology)

#### Section D

- Aleksi Vuorinen (University of Helsinki)

#### Section D

- Chihiro Sasaki (University of Wroclaw)

#### Section D

- Ilias Kyritsis (University of Crete (GR) and APC (FR))

#### Section D

- Jacopo Ghiglieri (Universitaet Bern (CH))

#### Section D

- Edmond Iancu (CEA/IRFU,Centre d'etude de Saclay Gif-sur-Yvette (FR))

#### Section D

- Aleksi Vuorinen (University of Helsinki)

#### Section D

- Malgorzata Anna Janik (Warsaw University of Technology (PL))

#### Section D

- Nan Su (Frankfurt Institute for Advanced Studies)

#### Section D

- Malgorzata Anna Janik (Warsaw University of Technology (PL))

### Description

Section D: Deconfinement

QCD at finite temperature; quark-gluon plasma detection and characteristics; jet quenching; transportation coefficients; lattice QCD and phases of quark matter; QCD vacuum and strong fields; heavy-ion experiments.

Conveners: C. Allton (Swansea U.), E. Iancu (CEA/DSM/Saclay), M. Janik (WUT), P. Petreczky (BNL), A. Vuorinen (U. Helsinki), Y. Foka (GSI)

Kinetic theory is one of the main dynamical frameworks to model ultrarelativistic heavy-ion collisions at RHIC and the LHC. For example, it has been used to study i) thermalization during the early partonic stage of the collision, ii) hadronic mixture evolution in late stages of the reaction, and more recently also iii) proper inclusion of nonthermal phase space density corrections for...

N/A

We numerically solve 2+1D effective kinetic theory of weak coupling QCD under longitudinal

expansion relevant for early stages of heavy-ion collisions. We find agreement with viscous hydrodynamics and classical Yang-Mills simulations in the regimes where they are applicable. With a reasonable initial condition for the anisotropic system in the heavy ion collisions, we found that the system...

Soft particle production in ultrarelativistic heavy-ion collisions is surprisingly well described by the "flow paradigm" which states that particles are emitted independently, according to a one-particle probability distribution that fluctuates event to event. I review some consequences of this flow paradigm and show how it can be used to relate correlations of different orders.

Anisotropic flow studies play a crucial role in improving our understanding of the behaviour and the nature of matter created in collisions of heavy ions. The different flow harmonics ($v_n$) harmonics for identified particles can be used to constrain the initial conditions and the value of shear viscosity over entropy density ratio. These studies allow also to reveal the role of the hadronic...

General aspects of the application of hydrodynamics in theoretical description of heavy-ion collisions are shortly reviewed with the emphasis on the following issues: fluid variables, the form of hydrodynamic expansion, early thermalization vs. early hydrodynamization scenario, the use of the realistic equation of state, incorporation of the phase transition and pre-equilibrium flow, free...

Observation of novel long-range collective phenomena in high-multiplicity pp and pA collisions at the LHC has opened up new opportunities of exploring QCD dynamics in a high-density environment. Major progress in experimental and theoretical community has been made in recent years to unravel the physical origin of the observed phenomena. In this talk, I will review the experimental results...

Anisotropic hydrodynamics is a reformulation of relativistic viscous hydrodynamics which allows one to more reliably describe non-equilibrium fluid dynamics. This is accomplished by taking into account inherent local-rest-frame momentum-space anisotropies at leading order. Through comparisons with recently obtained exact solutions to the Boltzmann equation, it has been shown that anisotropic...

I discuss calculations of the Polyakov loop and of Polyakov loop correlators using lattice gauge theory.

I briefly review recent calculations (since Conf. 2014) of the Polyakov loop and static quark correlators.

I cover in detail results in QCD with 2+1 flavors and almost physical quark masses using the highly improved staggered quark action (HISQ).

I examine the short- and long-distance...

Due to the non-Abelian nature of QCD and the existence of the 3-gluon coupling, the wavefunction of a high energy hadron at small-x is dominated by gluons (with x the longitudinal momentum fraction of a parton). The occupation numbers for these soft gluons increase rapidly with decreasing x and eventually saturate to their maximal allowed value, in a region where the coupling is still weak....

A full understanding of the spacetime evolution of the QCD matter created in a heavy ion collision requires understanding the properties of the initial stages. In the weak coupling picture these are dominated by classical gluon fields, whose properties can also be studied via the scattering of dilute probes off a high energy hadron or nucleus. A particular challenge is understanding small...

The magnitude of axial U(1) symmetry breaking is believed to affect the nature of phase transition in QCD with two light quark flavors. I review the recent studies on the fate of axial U(1) in finite temperature QCD using lattice techniques. Most of them investigate the eigenvalue spectrum of the fermion Dirac operator in QCD. The current understanding from majority of these studies is that...

We will present recent results regarding chiral symmetry restoration and other hadronic properties at finite temperature. In particular, we will discuss the interpretation of the temperature dependence of lattice screening masses through Ward identities relating pseudoscalar susceptibilities and quark condensates. Such identities are derived for two and three flavours and studied within the...

The combination of multiple particle identification systems along with the excellent tracking capabilities makes ALICE a unique tool for the measurement of light flavor hadron production over a broad transverse momentum ($p_{\rm T}$) range.

The production of $\pi^{\pm}$, $\mathrm{K}^{\pm}$, ${\rm K}^{0}_{S}$, $\rm p$,

$\rm\overline{p}$, $\Lambda$, $\bar{\Lambda}$, $\Xi^-$,...

We discuss the importance of initial state effects with regard to the theoretical understanding of long range azimuthal correlations observed in high-multiplicity p + p and p + A collisions at RHIC and the LHC. Starting with a brief overview of different effects, we perform a systematic comparison of initial state calculations with experimental data and briefly discuss progress towards...

At zero temperature nucleons and their parity partners have non-degenerate

masses due to spontaneous breaking of chiral symmetry.

However, chiral symmetry is expected to be restored at sufficiently high temperature,

in particular when going from the hadronic to the quark-gluon plasma (QGP) phase,

implying that the parity partners should become degenerate.

We study the nucleon (spin 1/2)...

A novel approach to identify the geometrical (anti)clusters formed by the Polyakov loops of the same sign and to study their properties in the lattice SU(2) gluodynamics is developed. The (anti)cluster size distributions are analyzed for the lattice coupling constant $\beta$=[2.3115; 3]. The found distributions are similar to the ones existing in 2- and 3-dimensional Ising systems [1]. Using...

Identified hadron spectra are considered to be sensitive to transport properties of strongly interacting matter produced in high-energy nucleus-nucleus collisions.

π0 and η mesons in ALICE are identified via their two-photon decays by using calorimeters and the central tracking system. In the latter, photons are measured via their conversion to electron-positron pairs on the material of the...

Heavy quarkonium presents a unique observable for the study of the quark-gluon plasma in relativistic heavy-ion collisions. While Bottomonium is expected to act as a test particle traversing the medium in the collision center, recent measurements of finite $J/\psi$ flow by the ALICE collaboration hint at the participation of the charm quarks in the collectivity of the bulk.

Here we present...

Based on arXiv:1410.6448, arXiv:1512.06445 and ongoing works

We explain the approach to thermal equilibrium of strongly coupled non-conformal plasmas using the AdS/CFT correspondence. The theories we study are the holographic duals to Einstein gravity coupled to a scalar with an exponential potential. The coefficient in the exponent, X, is the parameter that controls the deviation from the conformally invariant case. For these models we obtain analytic...

The modification of charmonium and bottomonium production in heavy ion collisions can provide information about the properties of the QGP, including the color screening length. But heavy quarkonia production can be modified by effects that precede QGP formation, as well as by effects that occur after hadronization. This requires that we study quarkonia formation in p+A collisions as well as...

Since the first heavy-ion collisions which date back to thirty years ago, quarkonium is considered one among the most important probes of the formation of a plasma of quarks and gluons.

Quarkonium production is, in fact, expected to be strongly modified by the creation of a hot medium. On one side, quarkonium yields are suppressed, due to the Debye screening, with respect to those measured in...

Using the AdS/CFT correspondence, phenomenological models based on five-dimensional Einstein-Dilaton gravity can be constructed which give a realistic description of several non-perturbative properties of Yang-Mills theory at thermal equilibrium. These models can also be used to describe time-dependent and out-of-equilibrium processes, and to compute observables related to heavy quark...

Heavy quarks, i.e. charm and beauty, are produced primarily in the initial, hard partonic scatterings in hadronic collisions.

In pp collisions, their production is well described by perturbative QCD due to their large mass.

In heavy-ion collisions, heavy quarks propagate through and interact with the hot and dense QCD matter.

Therefore, measurements of heavy-flavour production provide...

We compute the QGP suppression of $\Upsilon(1s)$, $\Upsilon(2s)$, $\Upsilon(3s)$, $\chi_{b1}$, and $\chi_{b2}$ states in \mbox{$\sqrt{s_{NN}}=2.76$ TeV} Pb-Pb collisions. Using the suppression of each of these states, we estimate the inclusive $R_{AA}$ for the $\Upsilon(1s)$ and $\Upsilon(2s)$ states as a function of $N_{\rm part}$, $y$, and $p_T$ including the effect of excited state feed...

Motivated by the striking modifications of jets observed both at RHIC and the LHC, significant progress towards the understanding of jet dynamics within QGP has occurred over the last few years. In this talk, I review the recent theoretical developments in the study of medium-induced jet evolution and energy loss within a perturbative framework. The main mechanisms of energy loss and...

We discuss the evolution of an energetic jet which propagates through a dense quark-gluon plasma

and radiates gluons due to its interactions with the medium. Within perturbative QCD, this

evolution can be described as a stochastic branching process, that we have managed to solve exactly.

We present exact, analytic, results for the gluon spectrum (the average gluon distribution)

and for...

The research programme of the ALICE experiment at the LHC focuses on studies of the Quark-Gluon Plasma, a state of matter where quarks and gluons are deconfined. The measurement of jets originating from the fragmentation of hard-scattered partons in the early phases of a nuclear collision allows one to study parton energy loss in the hot and dense medium. The dependence of the energy loss on...

Long-range multiplicity correlations in intervals separated in pseudorapidity and azimuth are studied in the framework of string fusion approach.

We applied a Monte Carlo model [1,2], in which the string configurations in the transverse plane and rapidity are simulating event-by-event.

We assumed that the azimuthal anisotropy of particle production is caused by parton energy loss travelling...

We use holography to analyze the evolution of an ensemble of jets, with an initial probability distribution for their energy and opening angle as in proton-proton (pp) collisions, as they propagate through an expanding cooling droplet of strongly coupled plasma as in heavy ion collisions. We identify two competing effects: (i) each individual jet widens as it propagates; (ii) the opening angle...

We calculate the next-to-next-to-leading correction to the expectation value of the Polyakov loop or equivalently to the free energy of a static charge. This correction is of order $g^5$. We show that up to this order the free energy of the static charge is proportional to the quadratic Casimir operator of the corresponding representation. We also compare our perturbative result with the most...

I review recent developments in QCD thermodynamics and collective excitations from the hard-thermal-loop effective theory. I begin by motivating the discussion with open questions from heavy-ion collisions. I then discuss a finite-temperature and density calculation of QCD thermodynamics at NNLO from the hard-thermal-loop perturbation theory. Finally, I discuss a recent exploration of...

The computation of single particle spectral functions and transport coefficients with functional continuum methods is discussed. Results are presented for quark and meson, and glueball spectral functions, as well as the temperature-dependent shear viscosity over entropy ratio.

We show that effective field theory techniques can be applied

in the high temperature T plasmas to

improve the accuracy of the physics of the hard scales ( or scales of order T).

At leading order in the

coupling constant the hard scales of the plasma can be viewed as

on-shell classical particles. Based on this observation, and without any

reference

to the state of the system, we...

We investigate the phase diagram of QCD with heavy quarks at finite temperature and chemical potential in the context of background field methods. In particular, we use a massive extension of the Landau-DeWitt gauge which is motivated by previous studies of the deconfinement phase transition in pure Yang-Mills theories. We show that a simple one-loop calculation is able to capture the richness...

In this talk I will review recent efforts in constraining the photon and dilepton rates on the theory side. This is achieved by extending perturbative calculations to next-to-leading order in the coupling $g$ both for photons and for dileptons in most kinematical regions. A polynomial interpolation for the corresponding spectral function, which vanishes at zero frequency and matches to these...

We present the results of a low-temperature scan of the phase diagram of

dense two-color QCD with N_f = 2 quarks. The study is conducted using lattice simulation

with rooted staggered quarks. At small chemical potential we observe the hadronic phase,

where the theory is in a confining state, chiral symmetry is broken, the baryon density is

zero and there is no diquark condensate. At the...

One of the most important result obtained at RHIC experiment is the measurement of the elliptic flow of final

particles. The value of this flow can be explained within hydrodynamic

approach, if it is assumed that QGP is nearly perfect fluid. Our paper is devoted to calculation of

shear viscosity of QGP at different temperatures within lattice simulation of QCD. The results of...

We study the effect of magnetic field on the photon emission

from the quark-gluon plasma (QGP) in AA collisions at RHIC and LHC energies.

We develop a formalism for photon radiation from the QGP

which accounts for interplay of the synchrotron mechanism and

the photon emission due to multiple scattering.

We show that multiple scattering suppresses strongly the

synchrotron contribution....

We derive three exact sum rules for the spectral function of the electromagnetic current channel at finite temperature, by using operator product expansion and hydrodynamics, focusing on zero spatial momentum case. We also discuss the possibility to use these sum rules to constrain and improve the functional form of the spectral function assumed in the lattice QCD analysis, and to evaluate the...

Electromagnetic probes are penetrating and are thus particularly useful to study the initial state and the earliest phases of hadron and heavy-ion collisions. However, because of the low cross section the measurements suffer from a small signal to background ratio and are therefore extremely challenging.

Prompt photon and Drell-Yan production are sensitive probes of the initial parton...

We study a Random Matrix Model for QCD at finite density via Complex Langevin dynamics. This model has a phase transition to a phase with non-zero baryon density. We study the convergence of the algorithm as a function of the quark mass and the chemical potential and focus on two main observables: the baryon density and the chiral condensate. As expected, for simulations close to the chiral...

We investigate the thermal-photon emission from strongly coupled gauge theories at finite temperature via the bottom-up models in holographic QCD in the deconfined phase. Particularly, we apply a model encoding flavor degrees of freedom in the Veneziano limit of a large number of colors $N_c$ and flavors $N_f$ but fixed $x=N_f=N_c$ (VQCD). In this model, the normalization and gauge-field...

We present results for correlators and spectral functions of open and hidden charm mesons using 2+1 flavours of clover fermions on anisotropic lattices. The D mesons are found to melt close to the deconfinement crossover temperature $T_c$. Our preliminary results suggest a shift in the thermal D meson mass below $T_c$.

Formation of color flux tubes (or quark-gluon strings), at very early stages of hadron- hadron collision, and the following hadronization, is the common general concept used by various event-generators of multiparticle production. The mechanisms of strings formation might be different (in soft and hard processes), however, the common feature in all model approaches is the number of strings...

At finite baryon density lattice QCD first-principle calculations can not be

performed due to the sign problem. In order to circumvent this problem, we

use the canonical approach, which provides reliable analytical continuation

from the $\mu_q^{Im.}$ region to the real chemical potential region. We briefly

present the canonical partition function method, describe our formulation, and

show...

Modifications in magnitude of fluctuations for different observables

are an excellent probe of a phase transition or its remnant.

In heavy-ion collision, fluctuations related to conserved charges

carried by light and strange quarks play an important role to identify

the QCD chiral crossover and deconfinement properties.

Recent Lattice QCD simulations have revealed that the charmed...

We present results from a calculation of the QCD equation of state up

to the sixth order in the baryon, strangeness and electric charge

chemical potentials. As the results depend on three independent chemical

potential, we consider various cases to parametrize the strangeness

and electric charge chemical potentials as a function of the baryon

chemical potential and temperature. Among...

Main physics goals of the NA61/SHINE programme on strong interactions

are the study of the properties of the onset of deconfinement and the search

for signatures of the critical point of strongly interacting matter. For these goals the scan through two dimensional phase diagram (T-$\mu_B$) is being performed

at the SPS by measurements of hadron production in nucleus-nucleus collisions

as...

In QCD many quantities, like bound states properties or positions of (pseudo-)phase transitions, can be calculated from the correlation functions of quarks and gluons. The correlation functions themselves can be determined non-perturbatively from various sets of functional equations. Here, truncated Dyson-Schwinger equations are employed for the study of the gluonic sector of QCD at non-zero...

An efficient way to study the QCD phase diagram at small finite density is to extrapolate thermodynamical observables from imaginary chemical potential. In this talk we present results on several observables for the equation of state to order (muB/T)^6. The observables are calculated along the isentropic trajectories in the (T, muB ) plane corresponding to the RHIC Beam Energy Scan collision...

The presence of collective expansion in small collision is discussed. Approaches based on relativistic hydrodynamics are compared to existing data. Possibilities to study fluctuations in the interaction region in small collision systems are described.