Extraction of the specific shear viscosity of quark-gluon plasma from two-particle transverse momentum correlations

TL;DR

This paper estimates the specific shear viscosity of quark-gluon plasma in heavy-ion collisions using two-particle transverse momentum correlations, revealing potential dependence on collision centrality at RHIC energies.

Contribution

It introduces a method to extract $ ext{eta}/s$ from $G_2$ correlator broadening using the Gavin ansatz and freeze-out time calculations, applied to STAR and ALICE data.

Findings

$ ext{eta}/s$ is roughly constant at LHC energies across centralities.

STAR data suggests $ ext{eta}/s$ may vary with collision centrality at RHIC.

The method links correlator broadening to shear viscosity through freeze-out dynamics.

Abstract

The specific shear viscosity, $\eta/s$, of the quark-gluon plasma formed in ultrarelativistic heavy-ion collisions at RHIC and LHC is estimated based on the progressive longitudinal broadening of transverse momentum two-particle correlators, $G_2$, reported as a function of collision centrality by the STAR and ALICE experiments. Estimates are computed as a function of collision centrality using the Gavin ansatz which relates the $G_2$ longitudinal broadening to the specific shear viscosity. Freeze out times required for the use of the ansatz are computed using a linear fit of freeze out times reported as a function of the cubic root of the charged particle pseudorapidity density $({\rm d}N_{\rm ch}/{\rm d}\eta)^{1/3}$. Estimates of $\eta/s$ based on ALICE data exhibit little to no dependence on collision centrality at LHC energy, while estimates obtained from STAR data hint that $\eta/s$ might be a function of collision centrality at top RHIC energy.