Saturation of $E_T/N_{ch}$ and Freeze-Out Criteria in Heavy-Ion Collisions

Abstract

The pseudorapidity densities of transverse energy, the charged particle multiplicity and their ratios, $E_T/N_{ch}$, are estimated at mid-rapidity, in a statistical-thermal model based on chemical freeze-out criteria, for a wide range of energies from GSI-AGS-SPS to RHIC. It has been observed that in nucleus-nucleus collisions, $E_T/N_{ch}$ increases rapidly with beam energy and remains approximately constant at about a value of 800 MeV for beam energies from SPS to RHIC. $E_T/N_{ch}$ has been observed to be almost independent of centrality at all measured energies. The statistical-thermal model describes the energy dependence as well as the centrality independence, qualitatively well. The values of $E_T/N_{ch}$ are related to the chemical freeze-out criterium, $E/N\approx 1GeV$ valid for primordial hadrons. We have studied the variation of the average mass $(<MASS>),N_{decays}/N_{primordial},N_{ch}/N_{decays}$ and $E_T/N_{ch}$ with $\sqrt{s_{NN}}$ for all freeze-out criteria discussed in literature. These observables show saturation around SPS and higher $\sqrt{s_{NN}}$, like the chemical freeze-out temperature ($T_{ch}$).

arXiv comment7 pages, 3 figures, ORAL presentation in 20th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM 2008), Jaipur, India, 4-10 Feb. 2008. To appear in Journal of Phys. G: Nucl. Part. Phys

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• Universal Freezeout Condition for Charged Hadrons in a Hybrid Approach
• Transverse Energy per Charged Particle in Heavy-Ion Collisions: Role of Collective Flow
• Probing the QGP Phase Boundary with Thermal Properties of $\varphi$ Mesons