Extraction of Kinetic Freeze-out Properties and Effect of Resonance Decays

Abstract

Abstract. We present STAR results from identified particle spectra measured in √ s N N = 62.4 GeV Au-Au collisions. Particle production and system dynamics are compared to results at √ s N N = 200 GeV. We extract kinetic and chemical freeze-out parameters using blast wave model parameterization and statistical model. We discuss the effect of resonance decays on the extracted kinetic freeze-out parameters.

Scaling properties at freeze-out in relativistic heavy-ion collisions

“…5 with results from most central 200-GeV Cu + Cu data. The π ± data points for p T < 0.5 GeV/c are excluded from the blast-wave fits to reduce the effects of resonance-decay contributions as done in previous works [5][6][7]. Including this low-p T region in the fit leads to a poorer description of proton and kaon shapes; however, the resultant modification of the extracted parameters remains well within their systematic uncertainty.…”

“…These 0%-60% minimum-bias events, with 24 M and 10 M events recorded at 200 and 62.4 GeV, respectively, were divided into six centrality bins, each corresponding to a 10% interval of the geometric cross section. Transverse mass distributions for charged pions, charged kaons, protons, and antiprotons, previously reported by STAR for √ s NN = 200 GeV pp collisions and Au + Au collisions at 62.4 and 200 GeV [5][6][7], are used for comparison. The STAR time projection chamber (TPC) [12] tracks particle trajectories over a wide range of momentum at midrapidity (|η| < 1.8).…”

“…Additional technical details on the analysis and applied corrections can be found in Refs. [5,6] with a thorough overview in Ref. [7].…”

“…The blast-wave model describes spectral shapes assuming a locally thermalized source with a common transverse flow velocity field. The results from Au + Au collisions at √ s NN = 200 and at 62.4 GeV [5][6][7] have shown that the chemical freeze-out temperature T ch has little dependence on centrality whereas the kinetic freeze-out temperature T kin decreases with increasing centrality of the collision. Furthermore, the radial flow velocity β increases with increasing centrality.…”

“…This suggests that chemical freeze-out coincides with hadronization and, therefore, T ch provides a lower-limit estimate for the temperature of the prehadronic state [9]. The systematic behavior of the kinetic freeze-out properties with charged hadron multiplicity appears to follow the same trend for all energies and systems at RHIC [5,6]. In this paper, the systematic studies of the QCD phase diagram from heavy-ion collisions are enriched by the addition of new RHIC data from Cu + Cu collisions at √ s NN = 200 and 62.4 GeV.…”