Radial flow and differential freeze-out in proton-proton collisions at √s=7 TeV at the LHC

Abstract

We analyse the transverse momentum (pT)-spectra as a function of charged-particle multiplicity at midrapidity (| y| < 0. 5) for various identified particles, such as π±, K±, KS0, p+ p¯ , ϕ, K* 0+ K* 0¯ , and Λ+ Λ¯ in proton-proton collisions at s=7 TeV using Boltzmann-Gibbs Blast Wave (BGBW) model and thermodynamically consistent Tsallis distribution function. We obtain the multiplicity-dependent kinetic freeze-out temperature (Tkin) and radial flow (β) of various particles after fitting the pT-distribution with BGBW model. Here, Tkin exhibits mild dependence on multiplicity class while β shows almost independent behaviour. The information regarding Tsallis temperature and the non-extensivity parameter (q are drawn by fitting the pT-spectra with Tsallis distribution function. The extracted parameters of these particles are studied as a function of charged particle multiplicity density (d N ch/ d η). In addition to this, we also study these parameters as a function of particle mass to observe any possible mass ordering. All the identified hadrons show a mass ordering in temperature, non-extensive parameter and also a strong dependence on multiplicity classes, except the lighter particles. It is observed that as the particle multiplicity increases, the q-parameter approaches to Boltzmann-Gibbs value, hence a conclusion can be drawn that system tends to thermal equilibrium. The observations are consistent with a differential freeze-out scenario of the produced particles. © 2019, SIF, Springer-Verlag GmbH Germany, part of Springer Nature.