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, $E/N \approx 1 GeV$ valid for primordial hadrons. We have studied the variation of the average 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 ($T_{ch}$).
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Submitted on : Monday, March 31, 2008 - 8:00:56 AM
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J. Cleymans, R. Sahoo, D. P. Mahapatra, D K Srivastava, S. Wheaton. Saturation of $E_T/N_{ch}$ and Freeze-Out Criteria in Heavy-Ion Collisions. 20th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM 2008), Feb 2008, Jaipur, India. 35, pp.104147, <10.1088/0954-3899/35/10/104147>. <in2p3-00268013>