Chemical freeze-out in ultrarelativistic heavy ion collisions atsNN=130and 200 GeV

Abstract

A comprehensive and detailed analysis of hadronic abundances measured in $\mathrm{Au}\text{\ensuremath{-}}\mathrm{Au}$ collisions at RHIC at $\sqrt{{s}_{\mathit{NN}}}=130$ and 200 GeV is presented. The rapidity densities measured in the central rapidity region have been fitted to the statistical hadronization model and the chemical freeze-out parameters determined as a function of centrality, using data from experiments BRAHMS, PHENIX, and STAR. The chemical freeze-out temperature turns out to be independent of centrality to accuracy of a few percentages, whereas the strangeness undersaturation parameter ${\ensuremath{\gamma}}_{S}$ decreases from almost unity in central collisions to a significantly lower value in peripheral collisions. Our results are in essential agreement with previous analyses, with the exception that fit quality at $\sqrt{{s}_{\mathit{NN}}}=200$ GeV is not as good as previously found. From the comparison of the two different energies, we conclude that the difference in fit quality, as described by ${\ensuremath{\chi}}^{2}$ values, is owing to the improved resolution of measurements that has probably exceeded the intrinsic accuracy of the simplified theoretical formula used in the fits.