Thermalization through parton transport

TL;DR

This paper uses a radiative transport model to study how partons in early relativistic heavy ion collisions approach thermalization, highlighting the roles of collisions, scaling behaviors, and viscosity in the process.

Contribution

It demonstrates that parton systems can partially thermalize through collisions, with radiative processes influencing scaling behaviors and the evolution of pressure anisotropy and energy density.

Findings

Pressure anisotropy shows alpha_s scaling with radiative processes.

Energy density decreases slower than ideal hydrodynamics predicts.

Partial thermalization is achievable with viscosity affecting early evolution.

Abstract

A radiative transport model is used to study kinetic equilibration during the early stage of a relativistic heavy ion collision. The parton system is found to be able to overcome expansion and move toward thermalization via parton collisions. Scaling behaviors show up in both the pressure anisotropy and the energy density evolutions. In particular, the pressure anisotropy evolution shows an approximate alpha_s scaling when radiative processes are included. It approaches an asymptotic time evolution on a time scale of 1 to 2 fm/c. The energy density evolution shows an asymptotic time evolution that decreases slower than the ideal hydro evolution. These observations indicate that partial thermalization can be achieved and viscosity is important for the evolution during the early longitudinal expansion stage of a relativistic heavy ion collision.