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

Understand

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).