Chemical freeze-out temperature in hydrodynamical description of Au+Au collisions at sqrt(s_NN) = 200 GeV

Abstract

We study the effect of separate chemical and kinetic freeze-outs to the ideal hydrodynamical flow in Au+Au collisions at RHIC (sqrt(s_NN) = 200 GeV energy). Unlike in earlier studies we explore how these effects can be counteracted by changes in the initial state of the hydrodynamical evolution. We conclude that the reproduction of pion, proton and antiproton yields necessitates a chemical freeze-out temperature of T = 150 MeV instead of T = 160 - 170 MeV motivated by thermal models. Unlike previously reported, this lower temperature makes it possible to reproduce the p_T-spectra of hadrons if one assumes very small initial time, tau_0 = 0.2 fm/c. However, the p_T-differential elliptic flow, v_2(p_T) remains badly reproduced. This points to the need to include dissipative effects (viscosity) or some other refinement to the model.