Systematics of Identified Particle Production in pp, dAu and Au-Au Collisions at RHIC Energies

TL;DR

This study analyzes identified particle spectra and freeze-out properties in pp, dAu, and Au-Au collisions at RHIC energies, revealing thermal and kinetic freeze-out conditions and their dependence on collision centrality and energy.

Contribution

It provides a comprehensive comparison of particle production and freeze-out parameters across different collision systems and energies, incorporating resonance decay effects.

Findings

Chemical freeze-out temperature is about 155 MeV across systems.

Kinetic freeze-out temperature decreases from peripheral to central collisions.

Resonance decays do not significantly alter spectral shapes in the measured pT region.

Abstract

(Abstract is abridged for arXiv.) Identified mid-rapidity particle spectra and freeze-out properties are presented for 200 GeV pp, 200 GeV dAu and 62.4 GeV Au-Au collisions, measured in the STAR-TPC. Evolution of the identified particle spectra ($\pi^{\pm}$, $K^{\pm}$, p and $\overline{p}$) with charged particle multiplicity and event centrality is investigated in detail. Thermal model fits to the measured particle ratios yield a chemical freeze-out temperature $\sim$ 155 MeV in 200 GeV pp, 200 GeV dAu and 62.4 GeV Au-Au collisions. The extracted chemical freeze-out temperature is close to the critical phase transition temperature predicted by lattice QCD calculations. The kinetic freeze-out temperature extracted from hydrodynamically motivated blast-wave models shows a continuous drop from pp, dAu and peripheral to central Au-Au collisions, while the transverse flow velocity increases from $\sim$ 0.2 in pp to $\sim$ 0.6 in central 200 GeV Au-Au collisions. The kinetic freeze-out parameters in 62.4 GeV and 200 GeV Au-Au collisions seem to be governed only by event multiplicity/centrality. In order to study the effect of resonance decays on the kinetic freeze-out parameters, the data are fitted with the blast-wave model including resonances. It is found that the thus extracted parameters are consistent with those obtained without including resonances, the resonance decays do not modify the spectral shapes significantly in the measured $p_{T}$ region in STAR.