Rise of azimuthal anisotropies as a signature of the Quark-Gluon-Plasma in relativistic heavy-ion collisions

TL;DR

This paper demonstrates that azimuthal anisotropies in heavy-ion collisions serve as effective signatures of the Quark-Gluon Plasma, with the PHSD model successfully describing energy-dependent flow patterns and highlighting the role of partonic degrees of freedom.

Contribution

The study introduces a comprehensive transport approach incorporating explicit partonic degrees of freedom to analyze azimuthal anisotropies across energies, emphasizing their sensitivity to the Quark-Gluon Plasma.

Findings

PHSD reproduces the energy dependence of elliptic flow $v_2$.

Higher-order flow harmonics $v_3$ and $v_4$ show increasing deviations between partonic and hadronic models at higher energies.

Azimuthal anisotropies are sensitive probes of the underlying degrees of freedom in heavy-ion collisions.

Abstract

The azimuthal anisotropies of the collective transverse flow of hadrons are investigated in a large range of heavy-ion collision energy within the Parton-Hadron-String Dynamics (PHSD) microscopic transport approach which incorporates explicit partonic degrees of freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as dynamical hadronization and hadronic dynamics in the final reaction phase. The experimentally observed increase of the elliptic flow $v_2$ with bombarding energy is successfully described in terms of the PHSD approach in contrast to a variety of other kinetic models based on hadronic interactions. The analysis of higher-order harmonics $v_3$ and $v_4$ shows a similar tendency of growing deviations between partonic and purely hadronic models with increasing bombarding energy. This signals that the excitation functions of azimuthal anisotropies provide a sensitive probe for the underling degrees of freedom excited in heavy-ion collisions.