Eur. Phys. J. A (2016) 52: 292
https://doi.org/10.1140/epja/i2016-16292-9

Regular Article - Theoretical Physics

Speed of sound in hadronic matter using non-extensive Tsallis statistics

¹ Discipline of Physics, School of Basic Science, Indian Institute of Technology Indore, Khandwa Road, 453552, Simrol, M.P., 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 February 2016
Accepted: 10 August 2016
Published online: 22 September 2016

Abstract

The speed of sound () is studied to understand the hydrodynamical evolution of the matter created in heavy-ion collisions. The quark-gluon plasma (QGP) formed in heavy-ion collisions evolves from an initial QGP to the hadronic phase via a possible mixed phase. Due to the system expansion in a first-order phase transition scenario, the speed of sound reduces to zero as the specific heat diverges. We study the speed of sound for systems which deviate from a thermalized Boltzmann distribution using non-extensive Tsallis statistics. In the present work, we calculate the speed of sound as a function of temperature for different q-values for a hadron resonance gas. We observe a similar mass cut-off behaviour in the non-extensive case for by including heavier particles, as is observed in the case of a hadron resonance gas following equilibrium statistics. Also, we explicitly show that the temperature where the mass cut-off starts varies with the q-parameter which hints at a relation between the degree of non-equilibrium and the limiting temperature of the system. It is shown that for values of q above approximately 1.13 all criticality disappears in the speed of sound, i.e. the decrease in the value of the speed of sound, observed at lower values of q, disappears completely.