Eur. Phys. J. A (2008) 35: 221-242
https://doi.org/10.1140/epja/i2007-10546-7

Regular Article - Theoretical Physics

Hadron production and phase changes in relativistic heavy-ion collisions

¹ Department of Physics, University of Arizona, 85721, Tucson, AZ, USA
² Laboratoire de Physique Théorique et Hautes Energies, Université Paris 7, 2 place Jussieu, F-75251 Cedex 05, Paris, France
³ CERN-PH-TH, 1211, Geneva 23, Switzerland

^* e-mail: rafelski@physics.arizona.edu

Received: 25 October 2007
Accepted: 8 February 2008
Published online: 11 March 2008

Abstract

We study soft hadron production in relativistic heavy-ion collisions in a wide range of reaction energy, 4.8 GeV < < 200 GeV, and make predictions about yields of particles using the statistical hadronization model. In fits to experimental data, we obtain both the statistical parameters as well as physical properties of the hadron source. We identify the properties of the fireball at the critical energy threshold, 6.26 GeV < < 7.61 GeV, marking for higher energies the hadronization of an entropy-rich phase. In terms of the chemical composition, one sees a phase which at low energy is chemically under-saturated, and which turns into a chemically over-saturated state persisting up to the maximum accessible energy. Assuming that there is no change in physical mechanisms in the energy range 15 > ≥200 GeV, we use continuity of particle yields and statistical parameters to predict the hadron production at = 62.4 GeV, and obtain total yields of hadrons at = 130 GeV. We consider, in depth, the pattern we uncover within the hadronization condition, and discuss possible mechanisms associated with the identified rapid change in system properties at . We propose that the chemically over-saturated 2 + 1 flavor hadron matter system undergoes a 1st-order phase transition.