Shear viscosity to entropy density ratio in the Boltzmann-Uehling-Uhlenbeck model

TL;DR

This study investigates the shear viscosity to entropy density ratio in intermediate energy heavy ion collisions using the BUU model, revealing it decreases with incident energy and approaches a value around 0.5.

Contribution

It applies the BUU model to compute the shear viscosity to entropy density ratio in heavy ion collisions at intermediate energies, linking microscopic dynamics to macroscopic transport properties.

Findings

$rac{ ext{eta}}{s}$ decreases with incident energy

$rac{ ext{eta}}{s}$ approaches ~0.5 at higher energies

Results are comparable to RHIC findings

Abstract

The ratio of shear viscosity ($\eta$) to entropy density ($s$) for an equilibrated system is investigated in intermediate energy heavy ion collisions below 100$A$ MeV within the framework of the Boltzmann-Uehling-Uhlenbeck (BUU) model . After the collision system almost reaches a local equilibration, the temperature, pressure and energy density are obtained from the phase space information and {$\eta/s$} is calculated using the Green-Kubo formulas. The results show that {$\eta$}/$s$ decreases with incident energy and tend towards a smaller value around 0.5, which is not so drastically different from the BNL Relativistic Heavy Ion Collider results in the present model.