Radial flow and differential freeze-out in proton-proton collisions at $\sqrt{s} = 7$ TeV at the LHC

Abstract.

We analyse the transverse momentum ($p_{T}$)-spectra as a function of charged-particle multiplicity at midrapidity ($\vert y\vert < 0.5$) for various identified particles, such as $\pi^{\pm}$, $K^{\pm}$, $K_{S}^{0}$, $p+\overline{p}$, $\phi$, $K^{\ast 0} + \overline{K^{\ast 0}}$, 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 ($T_{\rm kin}$) and radial flow ($\beta$) of various particles after fitting the p_T-distribution with BGBW model. Here, $T_{\rm kin}$ 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 $p_{\rm T}$-spectra with Tsallis distribution function. The extracted parameters of these particles are studied as a function of charged particle multiplicity density ($\rm{d} N_{ch}/ \rm{d} \eta$). 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.