The centrality dependence of v2/epsilon: the ideal hydro limit and eta/s

TL;DR

This paper investigates how elliptic flow scaled by eccentricity varies with collision centrality, using hydrodynamic models to relate it to the quark-gluon plasma's viscosity and ideal behavior.

Contribution

It introduces a two-parameter fit for the centrality dependence of v2/epsilon and relates these parameters to shear viscosity over entropy ratio and ideal hydro limit.

Findings

Parameters are proportional to shear viscosity over entropy ratio.

Parameters approximate the ideal hydrodynamic limit.

Fit accurately describes the centrality dependence of v2/epsilon.

Abstract

The large elliptic flow observed at RHIC is considered to be evidence for almost perfect liquid behavior of the strongly coupled quark-gluon plasma produced in the collisions. In these proceedings we present a two parameter fit for the centrality dependence of the elliptic flow scaled by the spatial eccentricity. We show by comparing to viscous hydrodynamical calculations that these two parameters are in good approximation proportional to the shear viscosity over entropy ratio and the ideal hydro limit of the ratio v2/epsilon.