Effects of EoS in viscous hydro+cascade model for the RHIC Beam Energy Scan

TL;DR

This study investigates how different equations of state influence the hydrodynamic evolution in heavy ion collisions within the RHIC Beam Energy Scan, revealing significant effects on model outcomes compared to a crossover EoS.

Contribution

It demonstrates the impact of a first-order phase transition EoS on viscous hydro+cascade model results across a range of collision energies, contrasting with a crossover EoS.

Findings

Effective shear viscosity ratio η/s decreases with collision energy.

First-order phase transition EoS alters hydrodynamic evolution.

Model results differ notably from crossover EoS scenarios.

Abstract

A state-of-the-art 3+1 dimensional cascade + viscous hydro + cascade model vHLLE+UrQMD has been applied to heavy ion collisions in RHIC Beam Energy Scan range $\sqrt{s_{\rm NN}}=7.7\dots 200$ GeV. Based on comparison to available experimental data it was estimated that an effective value of shear viscosity over entropy density ratio $\eta/s$ in hydrodynamic stage has to decrease from $\eta/s=0.2$ to $0.08$ as collision energy increases from $\sqrt{s_{\rm NN}} = 7.7$ to $39$ GeV, and to stay at $\eta/s=0.08$ for $39\le\sqrt{s_{\rm NN}}\le200$ GeV. In this work we show how an equation of state with first order phase transition affects the hydrodynamic evolution at those collision energies and changes the results of the model as compared to "default scenario" with a crossover type EoS from chiral model.