Exploring the partonic phase at finite chemical potential in and out-of equilibrium
O. Soloveva, P. Moreau, L. Oliva, T. Song, W. Cassing, E. Bratkovskaya
备注：
11 pages, 4 figures, contribution to the Proceedings of the 36th Winter Workshop on Nuclear Dynamics, 1-7 March 2020, Puerto Vallarta, Maxico. arXiv admin note: substantial text overlap with arXiv:2001.05395
We study the influence of the baryon chemical potential $μ_B$ on the properties of the Quark-Gluon-Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature $T_c$ from lattice Quantum Chromodynamics (QCD). We calculate the transport coefficients such as the ratio of shear viscosity $η$ and bulk viscosity $ζ$ over entropy density $s$, i.e., $η/s$ and $ζ/s$ in the $(T,μ_B)$ plane and compare to other model results available at $μ_B =0$. The out-of equilibrium study of the QGP is performed within the Parton-Hadron-String Dynamics (PHSD) transport approach extended in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections (based on the DQPM propagators and couplings) evaluated at the actual temperature $T$ and baryon chemical potential $μ_B$ in each individual space-time cell of the partonic scattering. The traces of their $μ_B$ dependences are investigated in different observables for relativistic heavy-ion collisions with a focus on the directed and elliptic flow coefficients $v_1, v_2$ in the energy range 7.7 GeV $\le \sqrt{s_{NN}}\le 200$ GeV.
We extend the Parton-Hadron-String Dynamics (PHSD) transport approach in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections as a function of temperature $T$ and baryon chemical potential $μ_B$ on the basis of the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature $T_c$ from lattice QCD. The ratio of shear viscosity $η$ over entropy density $s$, i.e. $η/s$, is evaluated using the collisional widths a…
We study the influence of the baryon chemical potential $μ_B$ on the properties of the Quark-Gluon-Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature $T_c$ from lattice QCD. We study the transport coefficients such as the ratio of shear viscosity $η$ and bulk viscosity $ζ$ over entropy density $s$, i.e. $η/s$ and $ζ/s$ in the $(T,μ)$ plane and compare to othe…
Following our previous proposal [1], we construct a class of good "lattice cross sections" (LCSs), from which we could study partonic structure of hadrons from ab initio lattice QCD calculations. These good LCSs, on the one hand, can be calculated directly in lattice QCD, and on the other hand, can be factorized into parton distribution functions (PDFs) with calculable coefficients, in the same way as QCD factorization for factorizable hadronic cross sections. PDFs could be extracted from QCD global analysis of the lattice QCD generated data of LCSs. We also show that proposed functions for la…
The parton yield, (pseudo)rapidity distribution, and transverse momentum distribution in partonic matter assumed forming in the early stage of $pp$ and nucleus-nucleus collisions at RHIC energy ($\sqrt{s_{NN}}$=200 GeV) and LHC energy ($\sqrt{s_{NN}}$=5.5 TeV for nucleus-nucleus, 5.5 and/or 14 TeV for $pp$) are comparatively investigated with parton and hadron cascade model PACIAE. It turned out that the different parton and anti-parton spectra approach to be similar with reaction energy increasing from RHIC to LHC. We have argued that if the partonic matter forming in Au+Au collisions at RHIC…
The interactions of heavy quarks with the partonic environment at finite temperature $T$ and finite quark chemical potential $μ_q$ are investigated in terms of transport coefficients within the Dynamical Quasi-Particle model (DQPM) designed to reproduce the lattice-QCD results (including the partonic equation of state) in thermodynamic equilibrium. These results are confronted with those of nuclear many-body calculations close to the critical temperature $T_c$. The hadronic and partonic spatial diffusion coefficients join smoothly and show a pronounced minimum around $T_c$, at $μ_q=0$ as well …
We study the possibility that partonic matter produced at early stage of ultrarelativistic heavy-ion collisions is out of chemical equilibrium. It is assumed that initially this matter is mostly composed of gluons, but quarks and antiquarks are produced at later times. The dynamical evolution of partonic system is described by the Bjorken-like ideal hydrodynamics with a time dependent quark fugacity. The results of this model are compared with those obtained by assuming the complete chemical equilibrium of partons already at the initial stage. It is shown that in a chemically non-equilibrium s…
The quark susceptibility $χ_q$ at zero and finite quark chemical potential provides a critical benchmark to determine the quark-gluon-plasma (QGP) degrees of freedom in relation to the results from lattice QCD (lQCD) in addition to the equation of state and transport coefficients. Here we extend the familiar dynamical-quasiparticle model (DQPM) to partonic propagators that explicitly depend on the three-momentum with respect to the partonic medium at rest in order to match perturbative QCD (pQCD) at high momenta. Within the extended dynamical-quasi-particle model (DQPM$^*$) we reproduce simult…
Using the string melting version of a multiphase transport model, we focus on the evolution of thermodynamic properties of the central cell of parton matter produced in Au$+$Au collisions ranging from 200 GeV down to 2.7 GeV. The temperature and chemical potentials have been calculated based on both Boltzmann and quantum statistics in order to locate their evolution trajectories in the QCD phase diagram. We demonstrate that the trajectories can depend on many physical factors, especially the finite nuclear thickness at lower energies. However, from the evolution of pressure anisotropy, only pa…
Using a partonic transport model based on the 3-flavor Nambu-Jona-Lasinio model and a relativistic hadronic transport model to describe, respectively, the evolution of the initial partonic and the final hadronic phase of heavy-ion collisions at energies carried out in the Beam-Energy Scan program of the Relativistic Heavy Ion Collider, we have studied the effects of both the partonic and hadronic mean-field potentials on the elliptic flow of particles relative to that of their antiparticles. We find that to reproduce the measured relative elliptic flow differences between nucleons and antinucl…
We present calculations for the shear viscosity of the hot and dense quark-gluon plasma (QGP) using the partonic scattering cross sections as a function of temperature $T$ and baryon chemical potential $μ_B$ from the dynamical quasiparticle model (DQPM) that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature $T_c$ from lattice QCD. To this aim we calculate the collisional widths for the partonic degrees of freedom at finite $T$ and $μ_B$ in the time-like sector and conclude that the quasiparticle limit holds sufficiently well. Furthermore, …
We analyze the reaction dynamics of central Pb+Pb collisions at 160 GeV/nucleon. First we estimate the energy density pile-up at mid-rapidity and calculate its excitation function: The energy density is decomposed into hadronic and partonic contributions. A detailed analysis of the collision dynamics in the framework of a microscopic transport model shows the importance of partonic degrees of freedom and rescattering of leading (di)quarks in the early phase of the reaction for E > 30 GeV/nucleon. The energy density reaches up to 4 GeV/fm^3, 95% of which are contained in partonic degrees of fre…
We investigate the QCD phase diagram for small values of baryon and strange quark chemical potentials from simulations at non-zero isospin chemical potential. Simulations at pure isospin chemical potential are not hindered by the sign problem and pion condensation can be observed for sufficiently large isospin chemical potentials. We study how the related phase boundary evolves with baryonic and strange chemical potentials via reweighting in quark chemical potentials and discuss our results. Furthermore, we propose and implement an alternative method to approach nonzero baryon (and strange qua…
We discuss recent experimental results on hadron multiplicities in ultra-relativistic nuclear collisions. The data for central collisions are in quantitative agreement with predictions of a thermal model assuming full chemical equilibration. It is argued that this provides strong, albeit indirect, evidence for the formation of a partonic phase in the collision prior to hadron production.
We study the kinetic and chemical equilibration in 'infinite' parton-hadron matter within the Parton-Hadron-String Dynamics transport approach, which is based on a dynamical quasiparticle model for partons matched to reproduce lattice-QCD results - including the partonic equation of state - in thermodynamic equilibrium. The 'infinite' matter is simulated within a cubic box with periodic boundary conditions initialized at different baryon density (or chemical potential) and energy density. The transition from initially pure partonic matter to hadronic degrees of freedom (or vice versa) occurs d…
We review the transport properties of the strongly interacting quark-gluon plasma (QGP) created in heavy-ion collisions at ultrarelativistic energies, i.e. out-of equilibrium, and compare them to the equilibrium properties. The description of the strongly interacting (non-perturbative) QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature $T_c$ from lattice QCD. We study the transport coefficients such as the ratio of shear…
We describe the transverse momentum spectra of $π^\pm$, $K^\pm$, $p$, and $\bar{p}$ produced in proton-proton ($pp$) collisions at different collision energies by using a Tsallis-Pareto-type function, and obtain the yield ratios, $k_π$, $k_{K}$, and $k_{p}$, of negative to positive particles from the fitting results of transverse momentum spectra and the extracted normalization constants. The transverse momentum dependent and energy dependent chemical potentials of light hadrons ($π$, $K$, and $p$) and quarks ($u$, $d$, and $s$) in $pp$ collisions are then extracted successively from the yield…
We calculate transport coefficients of the quark-gluon plasma (QGP) within the dynamical quasiparticle model (DQPM) by explicitly computing the parton interaction rates as a function of temperature $T$ and baryon chemical potential $μ_B$ on the basis of the DQPM couplings and partonic propagators. The latter are extracted from lattice QCD by matching the equation of state, entropy density and energy density at $μ_B$= 0. For baryon chemical potentials $0 \leq μ_B \leq 500 MeV$ we employ a scaling Ansatz for the effective coupling which was shown before to lead to thermodynamic consistent result…
Driven by the Beam Energy Scan (BES) program at the RHIC, researches and discussions on the QCD phase diagram have flourished recently. In order to provide a reference from microscopic transport models, we performed a systematic analysis, using a multiphase transport (AMPT) model for the particle yields and a statistical model (THERMUS) for the thermal fit, for Au+Au collisions at $\sqrt{s_{\text{NN}}}$=7.7-200 GeV. It is found that at a fixed collision centrality the chemical freeze-out parameter, temperature $T_{\text{ch}}$, increases with collision energy and somehow saturates at certain va…
Thermal model fit indicates early chemical freeze-out of multi-strange hadrons with small collective velocities at 200AGeV Au-Au collisions at RHIC. In this work, we present our recent results by SPheRIO hydrodynamical calculations inspired by this picture. In our model, multi-strange hadrons go through chemical freeze-out when the system reaches some temperature close to the phase transition, stopping to make inelastic collisions, and their abundances are therefore determined only by partonic EOS. At a lower temperature thermal freeze-out takes place where elastic collisions are brought to a …
We describe the transverse momentum (or mass) spectra of $π^\pm$, $K^\pm$, $p$, and $\bar{p}$ produced in central gold-gold (Au-Au), central lead-lead (Pb-Pb), and inelastic proton-proton ($pp$) collisions at different collision energies range from the AGS to LHC by using a two-component (in most cases) Erlang distribution in the framework of multi-source thermal model. The fitting results are consistent with the experimental data and the energy-dependent chemical potentials of light hadrons ($π$, $K$, and $p$) and quarks ($u$, $d$, and $s$) in central Au-Au, central Pb-Pb, and inelastic $pp$ …
We extend the effective dynamical quasiparticle model (DQPM) - constructed for the description of non-perturbative QCD phenomena of the strongly interacting quark-gluon plasma (QGP) - to large baryon chemical potentials, $μ_B$, including a critical end-point and a 1st order phase transition. The DQPM description of quarks and gluons is based on partonic propagators with complex selfenergies where the real part of the selfenergies is related to the quasiparticle mass and the imaginary part to a finite width of their spectral functions. In DQPM the determination of complex selfenergies for the p…
The Hadron-Resonance Gas (HRG) approach - used to model hadronic matter at small baryon potentials $μ_B$ and finite temperature $T$ - is extended to finite and large chemical potentials by introducing interactions between baryons in line with relativistic mean-field theory defining an interacting HRG (IHRG). Using lattice data for $μ_B=0$ as well as information on the nuclear equation of state at $T=0$ we constrain the attractive and repulsive interactions of the IHRG such that it reproduces the lattice equation of state at $μ_B=0$ and the nuclear equation of state at $T=0$ and finite $μ_B$. T…
The thermodynamic properties of proton rich systems are explored in a mean field approach which is generated from a Skyrme interaction. The addition of Coulomb interactions result in asymmetries which modify the chemical and mechanical instability of the system and its equilibrium properties. These properties are studied for systems with proton fraction $y$ on the proton richer side of the valley of $β$-stability as well as the neutron rich side. Coulomb induced instabilities lead to proton diffusion processes on the proton richer side and also large asymmetries in chemical and mechanical inst…
Quark number susceptibilities as computed in lattice QCD are commonly believed to provide insights into the microscopic structure of QCD matter, in particular its degrees of freedom. We generalize a previously constructed partonic $T$-matrix approach to finite chemical potential to calculate various susceptibilities, in particular for configurations containing a heavy charm quark. At vanishing chemical potential and moderate temperatures, this approach predicts large collisional widths of partons generated by dynamically formed hadronic resonance states which lead to transport parameters chara…
We put forward a Polyakov-loop extended quark meson model, where matter as well as glue fluctuations are taken into account, cf. [1]. The latter are included via a Polyakov-loop potential. Usually such a glue potential is based on Yang-Mills lattice data only. We show that a parametrisation of unquenching effects as proposed in [2], together with the inclusion of fluctuations via the functional renormalisation group [3,4], accounts for the relevant dynamics. This is demonstrated by a comparison of order parameters and thermodynamic observables to recent lattice results at vanishing chemical po…
We review the two standard equations of states based on the Nambu-Jona-Lasinio (NJL) model and the thermodynamic bag (tdBag) model for dense, cold quark matter from a perspective based on the Dyson-Schwinger (DS) formalism. A different, but technically not more complicated approximation reproduces the model of Munczek and Nemirovsky (MN) which accounts in a simplified way for chiral symmetry breaking and confinement as a dynamic process rooted in the momentum dependence of QCD model gap solutions. We review the mass gap solutions for the MN model in the chiral limit and sketch the behavior of …
We study SU(2) lattice gauge theory at non-zero chemical potential with one staggered quark flavor in the adjoint representation. In this model the fermion determinant, although real, can be both positive and negative. We have performed numerical simulations using both hybrid Monte Carlo and two-step multibosonic algorithms, the latter being capable of exploring sectors with either determinant sign. We find that the positive determinant sector behaves like a two-flavor theory, with the chiral condensate rotating into a two-flavor diquark condensate for mu>m_pi/2, implying a superfluid ground s…
Probing the QCD Phase Structure with Dileptons from SIS to LHC Energies
Frankfurt Institute for Advanced Studies (FIAS)（法兰克福高等研究所）；Helmholtz Research Academy Hessen for FAIR (HFHF)（黑森亥姆霍兹FAIR研究院）；GSI Helmholtz Center for Heavy Ion Physics（重离子物理亥姆霍兹中心）；Institute for Theoretical Physics, Johann Wolfgang Goethe University（约翰·沃尔夫冈·歌德大学理论物理研究所）；GSI Helmholtzzentrum fur Schwerionenforschung GmbH（重离子研究亥姆霍兹中心有限公司）；State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University（华南师范大学量子物质研究所核物理与技术国家重点实验室）
Based on the framework of an extended multiphase transport model with mean-field potentials in both the partonic phase and the hadronic phase, we explain the elliptic flow difference between $π^+$ and $π^-$ in the beam-energy scan program at the relativistic heavy-ion collider by incorporating the vector-isovector potential for quarks and antiquarks with different isospins. It is found that the isospin splitting of pion elliptic flow favors a strong vector-isovector interaction, and thus serves as a probe of the quark matter equation of state as well as the QCD phase structure at finite baryon…
The fundamental properties of dense nuclear matter, as it exists in the core of massive stellar objects, are still largely unknown. The investigation of the high-density equation of state (EOS), which determines mass and radii of neutron stars and the dynamics of neutron star mergers, is in the focus of astronomical observations and of laboratory experiments with heavy-ion collisions. Moreover, the microscopic degrees-of-freedom of strongly interacting matter at high baryon densities are also unknown. While Quantum-Chromo-Dynamics (QCD) calculations on the lattice find a smooth chiral crossove…
