Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV

TL;DR

This paper measures how the transverse momentum correlation function evolves with collision centrality in gold-gold collisions at 200 GeV, and uses this to estimate the medium's shear viscosity to entropy density ratio.

Contribution

First measurement of the differential transverse momentum correlation function's evolution with centrality in Au+Au collisions at 200 GeV, linking it to medium viscosity.

Findings

The correlation function shows strong centrality dependence.

The near-side peak broadening indicates low shear viscosity.

Estimated upper limit of η/s suggests a nearly perfect fluid.

Abstract

We present first measurements of the evolution of the differential transverse momentum correlation function, {\it C}, with collision centrality in Au+Au interactions at $\sqrt{s_{NN}} = 200$ GeV. {\it C} exhibits a strong dependence on collision centrality that is qualitatively similar to that of number correlations previously reported. We use the observed longitudinal broadening of the near-side peak of {\it C} with increasing centrality to estimate the ratio of the shear viscosity to entropy density, $\eta/s$, of the matter formed in central Au+Au interactions. We obtain an upper limit estimate of $\eta/s$ that suggests that the produced medium has a small viscosity per unit entropy.