FIZIKA B 18 (2009) 3, 141-150

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University of Bielefeld, P. O. Box 100131, D-33501 Bielefeld, Germany
Hiroshima University, 1-7-1 Kagami-yama, Higashi-Hiroshima, Japan
ECTP, MTI University, Mukattam, Cairo, Eqypt
E-mail address:

Received 23 September 2008;   Revised manuscript received 1 May 2009
Accepted 3 June 2009   Online 7 October 2009

We calculated different particle ratios in a wide range of energies 3.5 < {sNN} £ 200 GeV using the hadron resonance gas model, which was successfully applied in previous work to describe lattice QCD thermodynamics and characterize the phase transition and phase diagram lines. In this work, we assume that the particle production occurs along the freeze-out line, which has been defined by a constant entropy density normalized by temperature s/T3 at all collision energies. The quark phase space occupancy parameters, gi, have been allowed to take values other than one. Doing this, we are able to describe K+/p+ ratio over the whole range of energies, including the sharp peak observed at top SPS energies. The parameters resulting from this analysis have been applied in calculating K-/p-, L/p+ and L/pñ particle ratios and we found that within the statistical acceptance, the peaks in all these particle ratios occur in a very narrow range of the center-of-mass energy, {sNN} @ 7.5 GeV, which might be related to the baryo-chemical potential mB @ 0.43 GeV. We also find that the entropy per particle becomes maximum in this energy-region refering to fluctuations at QCD tricritical endpoint.

PACS numbers: 25.75.-q, 13.85.-t
UDC 539.172

Keywords: particle production ratio, heavy-ion collision, hadron resonance gas model, freeze-out line, ratios K+/p+, K-/p-, L/p+, L/pñ

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