Parton-Hadron-String Dynamics at Relativistic Collider Energies

TL;DR

The paper introduces the PHSD transport approach, which models the transition from partonic to hadronic matter in relativistic heavy-ion collisions, successfully reproducing experimental spectra and flow data at RHIC energies.

Contribution

The novel PHSD approach incorporates dynamical partonic phases based on lattice-QCD results, improving the description of heavy-ion collision observables over previous models.

Findings

Reasonable reproduction of hadron spectra and elliptic flow.

Fair description of elliptic flow as a function of centrality and transverse momentum.

Observation of approximate quark-number scaling of elliptic flow.

Abstract

The novel Parton-Hadron-String Dynamics (PHSD) transport approach is applied to nucleus-nucleus collisions at RHIC energies with respect to differential hadronic spectra in comparison to available data. The PHSD approach is based on a dynamical quasiparticle model for partons (DQPM) matched to reproduce recent lattice-QCD results from the Wuppertal-Budapest group in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark-antiquark pairs or three quarks (antiquarks), respectively, obeying flavor current-conservation, color neutrality as well as energy-momentum conservation. Our dynamical studies for heavy-ion collisions at relativistic collider energies are compared to earlier results from the Hadron-String Dynamics (HSD) approach - incorporating no explicit dynamical partonic phase - as well as to experimental data from the STAR, PHENIX, BRAHMS and PHOBOS collaborations for Au+Au collisions at the top RHIC energy of $\sqrt{s}$ = 200 GeV. We find a reasonable reproduction of hadron rapidity distributions and transverse mass spectra and also a fair description of the elliptic flow of charged hadrons as a function of the centrality of the reaction and the transverse momentum $p_T$. Furthermore, an approximate quark-number scaling of the elliptic flow $v_2$ of hadrons is observed in the PHSD results, too.