Freezeout conditions in proton-proton collisions from SPS to LHC energies

Sabita Das, Debadeepti Mishra, Sandeep Chatterjee, Bedangadas Mohanty

Published 2016-05-25Version 1

The freeze-out conditions in proton-proton collisions at $\sqrt{s_{\textrm{NN}}}= 17.3$, $200$, $900$ and $7000$ GeV have been extracted by fits to the mean hadron yields within the framework of the statistical model of an ideal gas of hadrons and resonances. The variation of the extracted freezeout thermal parameters and the goodness of the fits are discussed for: i. different choices of the statistical ensemble - canonical, strangeness canonical and grand canonical, and ii. different freezeout schemes - unified where all the hadrons freezeout together versus possible flavor dependence in freezeout. 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.