Nuclear modification factor in Pb–Pb and p-Pb collisions using Boltzmann transport equation

Abstract

We investigate the nuclear modification factor (RAA) of identified particles as a function of transverse momentum (pT) in Pb–Pb collisions at 2.76 and 5.02 TeV, as well as p-Pb collision at 5.02 TeV in the framework of Boltzmann transport equation with relaxation time approximation. In this framework, the initial distribution of particles is chosen as the Tsallis distribution and the local equilibrium distribution as the Boltzmann–Gibbs blast-wave distribution. The non-extensive parameter qpp, the Tsallis temperature Tpp and the equilibrium temperature Teq are set to be in common for all particles, while the ratio of kinetic freeze-out time to relaxation time tf/τ is different for different particles when we performed a combined fit to the RAA spectra of different particles at a given centrality. We observe that the fitted curves describe the spectra well up to pT ≈ 3 GeV/c. qpp and Teq (tf/τ) decrease (increases) with centrality nonlinearly, while Tpp is almost independent of centrality. The dependence of the rate at which qpp, Teq or tf/τ changes with centrality on the energy and the size of the colliding system is discussed.