What can we learn from the directed flow in heavy-ion collisions at BES RHIC energies?

TL;DR

This study analyzes the directed flow in heavy-ion collisions across a range of energies using different equations of state, finding that a crossover transition best explains experimental data and indicating deconfinement occurs over a broad energy range.

Contribution

It demonstrates that a crossover deconfinement transition model best fits experimental data and suggests the need for stiffer equations of state at high baryon densities.

Findings

Crossover EoS best describes experimental data.

Deconfinement transition occurs in a wide energy range.

Deconfinement EoS should be stiffer 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 the most part of experimental data in this energy range. The directed flow indicates that the crossover deconfinement transition takes place in semicentral Au+Au collisions in a wide range of collision energies 4 \lsim\sqrt{s_{NN}}\lsim$ 30 GeV. The obtained results suggest that the deconfinement EoS's 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.