Different Freezeout Scenarios in Large and Small Systems

摘要

83.1 Introduction The phase transition predicted by Quantum Chromodynamics (QCD) from ordinary matter to a deconfined Quark-Gluon Plasma (QGP) is being studied in high-energy heavy-ion (Pb+Pb) collisions at the Large Hadron Collider (LHC) by producing a hot and dense strongly interacting medium called the fireball. The expansion of the fireball causes dilution of the energy density of the system. The medium mean free path elongates and finally drives the fireball out of equilibrium. The identified hadron spectra and integrated yield provide insight into the particle production mechanism and interaction in the hadronic and QGP phases. The analysis of hadron yields allows an access to the properties of the chemical freezeout (CFO) surface where the hadronic inelastic collisions ceased [1-4]. Measurements in smaller collision systems such as proton-proton (p+p) and proton-lead (p+Pb) constitute a fundamental reference for the interpretation of the heavy-ion results. Here we have analysed the mid-rapidity data for hadron yields in Pb+Pb [5], p+Pb [6, 7] and p+p [8, 9] collisions at {formula}= 2.76, 5.02 and 7TeV respectively across all the available centralities. At these energies, the data reveals good particle-antiparticle symmetry which allow us to take the hadron chemical potentials to be zero. Thus the remaining parameters to be extracted from thermal fits are only the fireball volume, temperature and strangeness suppression factor at the time of freezeout.