Contrasting freezeouts in large versus small systems

Abstract

We study the data on mean hadron yields and contrast the chemical freezeout (CFO) conditions in p+p, p+Pb and Pb+Pb at the Large Hadron Collider energies. We study several schemes for freezeout that mainly differ in the way strangeness is treated: i. Strangeness freezes out along with the non-strange hadrons in complete equilibrium (1CFO), ii. Strangeness freezes out along with non-strange hadrons with an additional parameter accounting for non-equilibrium production of strangeness (1CFO+), and iii. Strangeness freezes out earlier than non-strange hadrons and in thermal equilibrium (2CFO). A comparison of the chisquares of the fits indicate a dependence of the freezeout scheme on the system size. The minimum bias p+p and different centralities of p+Pb and peripheral Pb+Pb data prefer 1CFO with approaching unity as we go from p+p to central p+Pb and peripheral Pb+Pb. On the other hand, the mid-central to central Pb+Pb data prefer 2CFO over 1CFO+. Such system size dependence of the freezeout scheme could be an indication of the additional interaction in Pb+Pb over p+Pb and p+p.