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

TL;DR

This study investigates how chemical freeze-out temperature and initial conditions affect hydrodynamical modeling of Au+Au collisions at RHIC, highlighting the need for viscosity effects to match elliptic flow data.

Contribution

It demonstrates that a lower chemical freeze-out temperature of 150 MeV can better reproduce particle yields and spectra when initial conditions are adjusted, challenging previous assumptions.

Findings

Chemical freeze-out at 150 MeV improves yield reproduction.

Small initial time (0.2 fm/c) can match p_T-spectra.

Elliptic flow remains poorly described, indicating missing physics.

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.