Radial flow and differential freeze-out in proton-proton collisions at TeV at the LHC

Arvind Khuntia; Himanshu Sharma; Swatantra Kumar Tiwari; Raghunath Sahoo; Jean Cleymans

doi:10.1140/epja/i2019-12669-6

2023 Impact factor 2.6

Hadrons and Nuclei

Eur. Phys. J. A (2019) 55: 3
https://doi.org/10.1140/epja/i2019-12669-6

Regular Article - Theoretical Physics

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

Arvind Khuntia¹, Himanshu Sharma¹, Swatantra Kumar Tiwari¹, Raghunath Sahoo¹^* and Jean Cleymans²

¹ Discipline of Physics, School of Basic Sciences, Indian Institute of Technology Indore, 453552, Indore, India
² UCT-CERN Research Centre and Department of Physics, University of Cape Town, 7701, Rondebosch, South Africa

^* e-mail: Raghunath.Sahoo@cern.ch

Received: 8 August 2018
Accepted: 4 December 2018
Published online: 18 January 2019

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.