title: Viscosity information from relativistic nuclear collisions: how perfect is the fluid observed at RHIC?
abstract: Relativistic viscous hydrodynamic fits to Brookhaven Relativistic Heavy Ion Collider data on the centrality dependence of multiplicity, transverse, and elliptic flow for square root s = 200 GeV Au+Au collisions are presented. For standard (Glauber-type) initial conditions, while data on the integrated elliptic flow coefficient v(2) are consistent with a ratio of viscosity over entropy density up to eta/s approximately 0.16, data on minimum bias v(2) seem to favor a much smaller viscosity over entropy ratio, below the bound from the anti-de Sitter conformal field theory conjecture. Some caveats on this result are discussed.
authors.affiliation: Institute for Nuclear Theory, University of Washington, Box 351550, Seattle, Washington 98195, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Romatschke
authors.forename: Ulrike
authors.initials: U
authors.lastname: Romatschke