Radial Flow and Differential Freeze-out in Proton-Proton Collisions at $\sqrt{s}=7$ TeV at the LHC

Abstract

We analyse the transverse momentum ($p_{\mathrm{T}}$)-spectra as a function of charged-particle multiplicity at midrapidity ($|y|<0.5$) for various identified particles such as ${\pi }^{\pm }$, $K^{\pm }$, $K_S^0$, $p+\overline{p}$, $\varphi$, $K^{\ast 0}+\overline{K^{\ast 0}}$, and $\Lambda$ + $\bar{\Lambda }$ in proton-proton collisions at $\sqrt{s}$ = 7 TeV using Boltzmann-Gibbs Blast Wave (BGBW) model and thermodynamically consistent Tsallis distribution function. We obtain the multiplicity dependent kinetic freeze-out temperature ($T_{\mathrm{kin}}$) and radial flow ($\beta$) of various particles after fitting the $p_{\mathrm{T}}$-distribution with BGBW model. Here, $T_{\mathrm{kin}}$ exhibits mild dependence on multiplicity class while $\beta$ shows almost independent behaviour. The information regarding Tsallis temperature and the non-extensivity parameter ($q$) are drawn by fitting the $p_{\mathrm{T}}$-spectra with Tsallis distribution function. The extracted parameters of these particles are studied as a function of charged particle multiplicity density ($d{N}_{ch}/d\eta$). 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.

Comments: Published version