Freezeout conditions in proton-proton collisions at the top RHIC and LHC energies

Abstract

The freezeout conditions in proton-proton collisions at $\sqrt{s_{\textrm{NN}}}= 200$, $900$ and $7000$ GeV have been extracted by fits to the mean hadron yields at mid-rapidity within the framework of the statistical model of an ideal gas of hadrons and resonances in the grand canonical ensemble. The variation of the extracted freezeout thermal parameters and the goodness of the fits with $\sqrt{s_{\textrm{NN}}}$ are discussed. We find the extracted temperature and baryon chemical potential of the freezeout surface to be similar in p+p and heavy ion collisions. On the other hand, the thermal behaviour of the strange hadrons is qualitatively different in p+p as compared to A+A. We find an additional parameter accounting for non-equilibrium strangeness production is essential for describing the p+p data. This is in contrast to A+A where the non-equilibrium framework could be successfully replaced by a sequential and complete equilibrium model with an early freezeout of the strange hadrons.