Particle Ratios and the QCD Critical Temperature

Abstract. We show how the measured particle ratios at RHIC can be used to provide non-trivial information about the critical temperature of the QCD phase transition. This is obtained by including the effects of highly massive Hagedorn resonances on statistical models, which are used to describe hadronic yields. Hagedorn states are relevant close to Tc and have been shown to decrease η/s to the KSS limit and allow for quick chemical equilibrium times in dynamical calculations of hadrons. The inclusion of Hagedorn states creates a dependence of the thermal fits on the Hagedorn temperature, TH, which is assumed to be equal to Tc, and leads to an overall improvement of thermal fits. We find that for Au+Au collisions at RHIC at sNN = 200 GeV the best square fit measure, χ2, occurs at Tc ∼ 176 MeV and produces a chemical freeze-out temperature of 170.4 MeV and a baryon chemical potential of 27.8 MeV. 1