Dissipation, Collective Flow and Mach Cones at RHIC

TL;DR

This paper uses a parton cascade model to study the rapid thermalization, elliptic flow, and jet quenching in QCD matter at RHIC, linking microscopic interactions to macroscopic phenomena.

Contribution

It provides a unified microscopic simulation of flow, jet-quenching, and shock waves in heavy-ion collisions, with dynamically extracted shear viscosity to entropy ratio.

Findings

Shear viscosity to entropy ratio $ ext{eta/s}$ is between 0.08 and 0.2.

Gluonic jets show slightly excessive suppression.

Shock wave development is hindered for $ ext{eta/s}$ > 0.2.

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 $v_2$ the shear viscosity to entropy ratio $\eta/s$ has been extracted dynamically and lies in the range of 0.08 and 0.2. Also jet-quenching has been investigated consistently within a full dynamical picture of the heavy ion collision. The results for gluonic jets indicate a slightly too large suppression, but are encouraging to understand the two major phenomena, strong flow and jet-quenching, within a unified microscopic treatment of kinetic processes. In addition, simulations on the temporal propagation of dissipative shock waves lead to the observation that an $\eta/s$ ratio larger than 0.2 prevents the development of well-defined shock waves on timescales typical for ultrarelativistic heavy-ion collisions.