Antiproton-to-proton ratios for ALICE heavy-ion collisions

Assuming that the final state of hadronization takes place along the freezeout line, which is defined by a constant entropy density, the antiproton-to-proton ratios produced in heavy-ion collisions are studied in framework of the hadron resonance gas (HRG) model. A phase transition from quark-gluon plasma to hadrons, a hadronization, has been conjectured in order to allow modifications in the phase-space volume and thus in the single-particle distribution function. Implementing both modifications in the grand-canonical partition function and taking into account the experimental acceptance in the heavy-ion collisions, the antiproton-to-proton ratios over center-of-mass energies,root s ranging from AGS to RHIC are very well reproduced by the HRG model. Comparing with the same particle ratios in pp collisions results in a gradually narrowing discrepancy with increasing root s. At LHC energy, the ALICE antiproton-to-proton ratios in the pp collisions turn to be very well described by the HRG model as well. It is likely that the ALICE A A-program will produce the same antiproton-to-proton ratios as the pp-one. Furthermore, the ratio gets very close to unity indicating that the matter antimatter asymmetry nearly vanishes. The chemical potential calculated at this energy strengthens the assumption of almost fully matter antimatter symmetry up to the LHC energy. (C) 2011 Elsevier B.V. All rights reserved.