Extracting the QGP viscosity from RHIC data -- a status report from viscous hydrodynamics

TL;DR

This paper reviews recent advancements in causal viscous hydrodynamics for relativistic heavy ion collisions, analyzing uncertainties and comparing results with experimental data to constrain the QGP shear viscosity to less than 5/(4pi).

Contribution

It provides a comprehensive status report on viscous hydrodynamics, highlighting the robustness of the upper limit on QGP viscosity from RHIC data.

Findings

Upper limit on eta/s < 5/(4pi)

Uncertainties from initial conditions and other factors analyzed

Comparison with experimental data supports viscosity constraints

Abstract

We report recent progress on causal viscous hydrodynamics for relativistic heavy ion collisions. For fixed specific shear viscosity eta/s, uncertainties in the elliptic flow arising from initial conditions, equation of state, bulk viscosity and numerical viscosity, and the treatment of the highly viscous hadronic stage and freeze-out procedure are analysed. A comparison of current viscous hydrodynamic results with experimental data yields a robust upper limit eta/s < 5/(4pi).