Directed flow in heavy-ion collisions and its implications for astrophysics

TL;DR

This study analyzes directed flow in heavy-ion collisions across various energies using different equations of state, revealing implications for the stiffness of quark-gluon matter and the existence of massive hybrid stars.

Contribution

It compares hadronic and deconfinement equations of state in modeling directed flow, highlighting the need for a stiffer quark-gluon EoS at high densities, linking nuclear physics with astrophysics.

Findings

Crossover EoS fits data at lower energies (≤20 GeV).

Purely hadronic EoS fits data at higher energies (≥20 GeV).

Results suggest a stiffer quark-gluon EoS at high baryon densities.

Abstract

Analysis of directed flow ($v_1$) of protons, antiprotons and pions in heavy-ion collisions is performed in the range of collision energies $\sqrt{s_{NN}}$ = 2.7--39 GeV. Simulations have been done within a three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS with deconfinement transitions: a first-order phase transition and a smooth crossover transition. The crossover EoS is unambiguously preferable for the description of experimental data at lower collision energies $\sqrt{s_{NN}}\leq$ 20 GeV. However, at higher collision energies $\sqrt{s_{NN}}\geq$ 20 GeV the purely hadronic EoS again becomes advantageous. This indicates that the deconfinement EoS in the quark-gluon sector should be stiffer at high baryon densities than those used in the calculation. The latter finding is in agreement with that discussed in astrophysics in connection with existence of hybrid stars with masses up to about two solar masses.