Extraction of the Specific Shear Viscosity of Hot Hadron Gas

TL;DR

This paper estimates the specific shear viscosity of hot hadron gas in nuclear collisions using a blastwave model, fitting experimental data across various energies and conditions to understand its temperature and chemical potential dependence.

Contribution

It introduces a novel method applying blastwave parameterization to extract shear viscosity from experimental spectra and flow data in the hadronic phase.

Findings

Estimated $ ext{η/s}$ ranges from 0.1 to 0.2 across studied temperatures.

Systematic uncertainties are carefully assessed and included.

Results are consistent with theoretical predictions for hadronic matter.

Abstract

We extract the specific shear viscosity $\eta/s$ of nuclear matter for various temperatures and chemical potentials in the hadronic phase using data taken in high energy nuclear collisions. We use a blastwave parameterization of the final state of nuclear collisions, including non-equilibrium deformations of particle distributions due to shear stress in the Navier-Stokes approximation. We fit spectra and elliptic flow of identified hadrons for a variety of collision energies and impact parameters at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The systems analyzed cover a temperature range from about 110 to 140 MeV and vary in their chemical potentials for stable hadrons. We attempt to assign meaningful systematic uncertainties to our results. This work is complementary to efforts using viscous fluid dynamics to extract the specific shear viscosity of quark gluon plasma at higher temperatures. We put our work in context with existing theoretical calculations of the specific shear viscosity.