Knudsen number, ideal hydrodynamic limit for elliptic flow and QGP viscosity in $\sqrt{s}$=62 and 200 GeV Cu+Cu/Au+Au collisions

TL;DR

This paper estimates the QGP viscosity, inverse Knudsen number, and ideal hydrodynamic limit for elliptic flow in high-energy Cu+Cu and Au+Au collisions, accounting for entropy generation during viscous evolution.

Contribution

It provides new estimates of QGP viscosity and inverse Knudsen number in heavy-ion collisions, considering entropy production, which enhances understanding of QGP properties.

Findings

Viscosity to entropy ratio estimated as 0.17±0.10±0.20.

Inverse Knudsen number around 2.80±1.63 in central Au+Au collisions.

Ideal hydrodynamic elliptic flow exceeds experimental flow by about 40% in central collisions.

Abstract

Taking into account of entropy generation during evolution of a viscous fluid, we have estimated inverse Knudsen number, ideal hydrodynamic limit for elliptic flow and QGP viscosity to entropy ratio in $\sqrt{s}$=62 and 200 GeV Cu+Cu/Au+Au collisions. Viscosity to entropy ratio is estimated as $\eta/s=0.17\pm 0.10\pm 0.20$, the first error is statistical, the second one is systematic. In a central Au+Au collision, inverse Knudsen number is $\approx 2.80\pm 1.63$, which presumably small for complete equilibration. In peripheral collisions it is even less. Ideal hydrodynamic limit for elliptic flow is $\sim$40% more than the experimental flow in a central collision.