Universal pion freeze-out phase-space density

TL;DR

This paper investigates the pion phase-space density at freeze-out across various collision types, revealing thermal behavior consistent with Bose-Einstein distribution at specific temperatures and flow conditions.

Contribution

It provides a comparative analysis of pion freeze-out densities in different collision systems, highlighting temperature and flow differences.

Findings

Heavy-ion reactions align with Bose-Einstein distribution at T ~ 120 MeV.

pi-p collisions fit the distribution at T ~ 180 MeV without radial flow.

Results suggest different freeze-out conditions in heavy-ion and pi-p collisions.

Abstract

Results on the pion phase-space density at freeze-out in sulphur-nucleus, Pb-Pb and pi-p collisions at the CERN SPS are presented. All heavy-ion reactions are consistent with the thermal Bose-Einstein distribution f=1/[exp(E/T)-1] at T ~ 120 MeV, modified for radial expansion. pi-p data are also consistent with f, but at T ~ 180 MeV and without radial flow.