Abstract
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 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 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 and the evaluated at actual temperature T and baryon chemical potential μ B in each individual space-time cell where partonic scattering takes place. The traces of their μ B dependences are investigated in different observables for symmetric Au + Au and asymmetric Cu + Au collisions such as rapidity and m T -distributions and directed and elliptic flow coefficients v 1 , v 2 in the energy range 7.7 GeV ≤ s N N ≤ 200 GeV.
Highlights
The phase diagram of matter is one of the most fascinating subjects in physics, which has important implications on chemistry and biology
We find that the Dynamical QuasiParticle Model (DQPM) result for ζ/s is in very good agreement with the lattice Quantum Chromodynamics (QCD) results and shows a rise closer to TC contrary to the holographic results, which show practically a constant behavior independent of model parameters
The cross sections depend explicitly on the invariant energy of the colliding partons s and on T. This is realized in the PHSD5.0 by setting μB = 0, cf. [17]. (3) ‘PHSD5.0 - μB’: the masses and widths of quarks and gluons depend on T and μB explicitly; the differential and total partonic cross sections are obtained by calculation√s of the leading order Feynman diagrams from the DQPM and explicitly depend on invariant energy s, temperature T and baryon chemical potential μB
Summary
The phase diagram of matter is one of the most fascinating subjects in physics, which has important implications on chemistry and biology. These transport coefficients emerge from the stationary limit of correlators and provide additional information on the systems in thermal and chemical equilibrium apart from the equation of state In this context, the phase diagram of strongly interacting matter has been the topic of most interest for decades and substantial experimental and theoretical efforts have been invested to shed light on this issue. Since relativistic heavy-ion collisions start with impinging nuclei in their groundstates, a proper non-equilibrium description of the entire dynamics through possibly different phases up to the final asymptotic hadronic states—eventually showing some degree of equilibration—is mandatory To this aim, the Parton–Hadron–String Dynamics (PHSD) transport approach [5,12,13,14,15] has been formulated more a decade ago (on the basis of the Hadron-String-Dynamics (HSD) approach [16]), and it was found to well describe observables from p+A and A+A collisions from SPS to LHC energies including electromagnetic probes such as photons and dileptons [5]. We show explicitly the ‘bulk’ results for asymmetric heavy-ion collisions such as Cu+Au and discuss which hadronic species and observables are more sensitive to such effects
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