Heavy Ion Tea

Has elliptic flow reached ideal hydrodynamical limit at RHIC ?
Hiroshi Masui (LBNL)

Abstract: First RHIC results of v2 reach predictions from ideal hydrodynamical model at most central Au + Au collisions. This result is one of the key observations that claims the finding of a nearly perfect fluid at RHIC. Recent progress in hydrodynamical models have been made to study the uncertainties of initial conditions, equation of states, viscous corrections and hadronic rescattering at late stage. Therefore, it is important for us to revisit how close the v2 is the ideal hydrodynamical limit at RHIC and whether we can constrain equation of state or viscosity from the data. I will present the recent v2 measurements at RHIC in 200 GeV Au +Au collisions, and discuss a simple approach motivated by a transport model to describe the centrality dependence of v2. I will further discuss the extent to which the v2 is away from the ideal hydrodynamical limit, and the validity and limitations of our approach to extract shear viscosity.