Viscous Effects on Elliptic Flow and Shock Waves

TL;DR

This paper uses a parton cascade model to study viscous effects on elliptic flow and shock waves in QCD matter, extracting viscosity ratios and simulating shock wave propagation.

Contribution

It introduces a detailed pQCD-based simulation approach to analyze viscous effects on elliptic flow and shock waves in QCD matter.

Findings

Shear viscosity to entropy ratio between 0.08 and 0.2.

Successful simulation of both ideal and viscous shock waves.

Quantitative extraction of viscosity from flow data.

Abstract

Fast thermalization and a strong buildup of elliptic flow of QCD matter as found at RHIC are understood as the consequence of perturbative QCD (pQCD) interactions within the 3+1 dimensional parton cascade BAMPS. The main contributions stem from pQCD bremsstrahlung $2 \leftrightarrow 3 $ processes. By comparing to Au+Au data of the flow parameter $v_2$ as a function of participation number the shear viscosity to entropy ratio is dynamically extracted, which lies in the range of 0.08 and 0.2, depending on the chosen coupling constant and freeze out condition. Furthermore, first simulations on the temporal propagation of dissipative shock waves are given. The cascade can either simulate true ideal shocks as well as initially diluted, truely viscous shocks, depending on the employed cross sections or mean free path, respectively.