Anisotropic Flow from Non-equilibrium Initial Condition with a Saturation Scale

Abstract

A current goal of relativistic heavy ion collisions experiments is to understand the impact of initial non-equilibrium on final observables. A Color Glass Condensate (CGC) as the limiting state of QCD matter at very high density implies initial non-thermal distribution at least for momenta below the saturation scale. In viscous hydrodynamics simulations, a standard Glauber initial condition leads to estimate 4πη/s ~ 1, while employing the Kharzeev-Levin-Nardi (KLN) modeling of the CGC leads to at least a factor of 2 larger η/s. Within a kinetic theory approach based on a relativistic Boltzmann-like transport simulation, our main result is that the out-of-equilibrium initial distribution in p-space reduces the effciency in building-up the elliptic flow. At RHIC energy we find the available data on υ2 are in agreement with a 4πη/s ~ 1 also for KLN initial conditions.