Extracting the shear viscosity of a high temperature hadron gas

TL;DR

This paper estimates the shear viscosity and relaxation time of a hot hadron gas in the temperature range relevant to heavy-ion collisions, aiding understanding of the quark-gluon plasma's transport properties.

Contribution

It provides the first extraction of shear viscosity over entropy ratio and estimates the shear viscous relaxation time for a high-temperature hadron gas.

Findings

Shear viscosity over entropy ratio is quantified between 120 MeV and 170 MeV.

Shear viscous relaxation time is estimated at 165 MeV.

Results help connect hadronic phase properties to quark-gluon plasma behavior.

Abstract

Quark-Gluon plasmas produced in relativistic heavy-ion collisions quickly expand and cool, entering a phase consisting of multiple interacting hadronic resonances just below the QCD deconfinement temperature. The transport properties of this hot hadron gas are poorly understood, yet they play an important role in our ability to infer transport properties of the quark-gluon plasma, because experimental measurements integrate over the whole system evolution. Assuming that the hot hadron gas can be modeled by a hadron cascade code based on kinetic theory assuming binary interactions, the shear viscosity over entropy ratio of a hot hadron gas for temperatures in between 120 MeV and 170 MeV is extracted. Furthermore, we present estimates for a second order transport coefficient, the shear viscous relaxation time at a temperature of 165 MeV.