Simulations of Statistical Model Fits to RHIC Data

The application of statistical model fits to experimentally measured particle multiplicity ratios allows inferences of the average values of temperatures, T, baryochemical potentials, $\mu_{\rm B}$, and other quantities at chemical freeze-out. The location of the boundary between the hadronic and partonic regions in the ($\mu_{\rm B}$,T) phase diagram, and the possible existence of a critical point, remains largely speculative. The search for a critical point using the moments of the particle multiplicity distributions in tightly centrality constrained event samples makes the tacit assumption that the variances in the ($\mu_{\rm B}$,T) values in these samples is sufficiently small to tightly localize the events in the phase diagram. This and other aspects were explored in simulations by coupling the UrQMD transport model to the statistical model code Thermus. The phase diagram trajectories of individual events versus the time in fm/$c$ was calculated versus the centrality and beam energy. The variances of the ($\mu_{\rm B}$,T) values at freeze-out, even in narrow centrality bins, are seen to be relatively large. This suggests that a new way to constrain the events on the phase diagram may lead to more sensitive searches for the possible critical point.