Event shape and Multiplicity dependence of Freeze-out Scenario and System Thermodynamics in Proton+Proton Collisions at $\sqrt{s}$ = 13 TeV using PYTHIA8

Abstract

Recent observations of QGP-like conditions in high-multiplicity pp collisions from ALICE experiment at the LHC warrants an introspection whether to use pp collisions as a baseline measurement to characterize heavy-ion collisions for possible formation of a Quark-Gluon Plasma. A double differential study of the particle spectra and thermodynamics of the produced system as a function of charged-particle multiplicity and transverse spherocity in pp collisions would shed light into the underlying event dynamics. Transverse spherocity, one of the event shape observables, allows to separate the events in terms of jetty and isotropic events. We analyse the identified particle transverse momentum ($p_{\rm T}$) spectra as a function of charged-particle multiplicity and transverse spherocity using Tsallis non-extensive statistics and Boltzmann-Gibbs Blastwave (BGBW) model in pp collisions at $\sqrt{s}$ = 13 TeV using PYTHIA8 event generator. The extracted parameters such as temperature ($T$), radial flow ($β$) and non-extensive parameter ($q$) are shown as a function of charged-particle multiplicity for different spherocity classes. We observe that the isotropic events approach to thermal equilibrium while the jetty ones remain far from equilibrium. We argue that, while studying the QGP-like conditions in small systems, one should separate the isotropic events from the spherocity-integrated events, as the production dynamics are different.