Scaling properties at freeze-out in relativistic heavy ion collisions

TL;DR

This study investigates how the size of the colliding system influences the freeze-out properties in relativistic heavy ion collisions, using spectra of identified particles and hydrodynamic models across different energies and system sizes.

Contribution

It extends the understanding of freeze-out parameters by analyzing Cu+Cu collisions and their dependence on system size, energy, and initial geometry, complementing previous Au+Au and pp studies.

Findings

Freeze-out properties scale with total charged particle multiplicity.

Initial state effects are significant in determining freeze-out characteristics.

System size dependence is consistent across different collision energies.

Abstract

Identified charged pion, kaon, and proton spectra are used to explore the system size dependence of bulk freeze-out properties in Cu+Cu collisions at $\sqrt{s_{NN}}$=200 and 62.4 GeV. The data are studied with hydrodynamically-motivated Blast-wave and statistical model frameworks in order to characterize the freeze-out properties of the system. The dependence of freeze-out parameters on beam energy and collision centrality is discussed. Using the existing results from Au+Au and $pp$ collisions, the dependence of freeze-out parameters on the system size is also explored. This multi-dimensional systematic study furthers our understanding of the QCD phase diagram revealing the importance of the initial geometrical overlap of the colliding ions. The analysis of Cu+Cu collisions, which expands the system size dependence studies from Au+Au data with detailed measurements in the smaller system, shows that the bulk freeze-out properties of charged particles studied here scale with the total charged particle multiplicity at mid-rapidity, suggesting the relevance of initial state effects.