A non-equilibrium picture of the chemical freeze-out in hadronic thermal   models
  Thermal models have proven to be an useful and simple tool used to make theoretical predictions and data analysis in relativistic and ultra-relativistic heavy ion collisions. A new version of these models is presented here, incorporating a non equilibrium feature to the description of the intermediate fireball state formed at the chemical freeze-out. Two different effective temperatures are attributed to the expanding fireball, regarding its baryonic and mesonic sectors. The proposal is not merely to include an additional degree of freedom to reach a better adjustment to the data, but to open a room in the model conception for considerations on the non-equilibrium scenario of the system evolution. A set of well consolidated data for particles production is used to validated the reformulated version of thermal models presented here. A rather good performance of the extended version was verified, both for the quality of particle ratio data fittings as well as for describing the asymptotic energy behavior of temperatures and baryochemical potential of the colliding nuclear system. 
Leonardo P. G. De Assis, Sergio B. Duarte, Marcelo Chiapparini,   Luciana R. Hirsch and Antonio Delfino
nucl-th hep-ph hep-th nucl-ex