Entropy Production and Effective Viscosity in Heavy-Ion Collisions

TL;DR

This study estimates entropy production and effective viscosity in heavy-ion collisions across a wide energy range using a three-fluid model, revealing rapid early entropy generation and a temperature-dependent viscosity-to-entropy ratio.

Contribution

It provides new estimates of entropy production and viscosity in heavy-ion collisions using a three-fluid model with various equations of state, including deconfinement transition effects.

Findings

Over 80% of entropy is produced during a short early collision stage.

The viscosity-to-entropy ratio ($ta/s$) ranges from ~0.05 to ~0.5 depending on energy.

$ta/s$ decreases with temperature approximately as $1/T^4$.

Abstract

Entropy production and an effective viscosity in central Au+Au collisions are estimated in a wide range of incident energies 3.3 GeV $\le \sqrt{s_{NN}}\le$ 39 GeV. The simulations are performed within a three-fluid model employing three different equations of state with and without deconfinement transition, which are equally good in reproduction of the momentum-integrated elliptic flow of charged particles in the considered energy range. It is found that more that 80\% entropy is prodused during a short early collision stage which lasts $\sim$1 fm/c at highest considered energies $\sqrt{s_{NN}}\ge$ 20 GeV. The estimated values of the viscosity-to-entropy ratio ($\eta/s$) are approximately the same in all considered scenarios. At final stages of the system expansion they range from $\sim$0.05 at highest considered energies to $\sim$0.5 lowest ones. It is found that the $\eta/s$ ratio decreases with the temperature ($T$) rise approximately as $\sim 1/T^4$ and exhibits a rather weak dependence on the net-baryon density.