CERN Heavy Ion Forum on Hydrodynamics

Wednesday 5 Sept 2007, 10:30 → 12:30 Europe/Zurich

TH Theory Conference Room (CERN)

1. "How perfect is the RHIC fluid?"
Paul Romatschke, Institute for Nuclear Theory, Univ. of Washington

I will discuss equations for causal viscous relativistic hydrodynamics and present 2+1 dimensional viscous hydrodynamic fits to RHIC data for sqrt(s)=200 GeV Au+Au collisions. Using Glauber-type initial conditions, these fits indicate that the ratio shear viscosity over entropy density is indeed very small; taking minimum bias data for elliptic flow at face value, a ratio that is smaller than the minimum bound from AdS/CFT is favored. Some caveats of this result are addressed.

2. "Recent results on fireball evolution, hadron spectra and elliptic flow from (2+1)-dimensional viscous hydrodynamics"
Ulrich Heinz, CERN and Ohio State University

We report on first results from a newly developed code that solves the causal Israel-Stewart hydrodynamic equations for a dissipative relativistic fluid with RHIC initial conditions. We assume longitudinal boost-invariance and solve the equations of motion in the two dimensions transverse to the beam. We explore in some detail the space-time evolution of the viscous corrections to the energy-momentum tensor and study their effects on transverse momentum spectra and elliptic flow for hadrons produced in RHIC collisions. We see unexpectedly strong shear viscosity effects on the elliptic flow which is strongly suppressed relative to ideal fluid dynamics. If our preliminary results hold up to further scrutiniy, RHIC data may require shear viscosity values for the QGP that are below the conjectured lower limit recently derived from the AdS/CFT correspondence.