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

We investigate the nuclear modification factor ($R_{AA}$) of identified particles as a function of transverse momentum ($p_{\rm T}$) in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=$ 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 $q_{pp}$, the Tsallis temperature $T_{pp}$ and the equilibrium temperature $T_{eq}$ are set to be in common for all particles, while the ratio of kinetic freeze-out time to relaxation time $t_{f}/τ$ is different for different particles when we performed a combined fit to the $R_{AA}$ spectra of different particles at a given centrality. We observe that the fitted curves describe the spectra well up to $p_{\rm T}\approx$ 3 GeV/c. $q_{pp}$ and $T_{eq}$ ($t_{f}/τ$) decrease (increases) with centrality nonlinearly, while $T_{pp}$ is almost independent of centrality. The dependence of the rate at which $q_{pp}$, $T_{eq}$ or $t_{f}/τ$ changes with centrality on the energy and the size of the colliding system is discussed.

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