Particle Ratios and the QCD Critical Temperature

TL;DR

This paper demonstrates how particle ratios measured at RHIC can inform the critical temperature of the QCD phase transition by incorporating Hagedorn resonances into statistical models, improving thermal fit accuracy.

Contribution

It introduces the inclusion of Hagedorn states into thermal models to better estimate the QCD critical temperature from experimental data.

Findings

Best fit at T_c ~ 176 MeV for RHIC Au+Au collisions

Chemical freeze-out temperature of 170.4 MeV

Baryon chemical potential of 27.8 MeV

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 $T_c$ and have been shown to decrease $\eta/s$ 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, $T_H$, which is assumed to be equal to $T_c$, and leads to an overall improvement of thermal fits. We find that for Au+Au collisions at RHIC at $\sqrt{s_{NN}}=200$ GeV the best square fit measure, $\chi^2$, occurs at $T_c \sim 176$ MeV and produces a chemical freeze-out temperature of 170.4 MeV and a baryon chemical potential of 27.8 MeV.