Identified particle spectra in Pb–Pb, Xe–Xe and p–Pb collisions with the Tsallis blast-wave model

Abstract

We investigate the hadron transverse momentum (p T) spectra in Pb–Pb (Pb–Pb, Xe–Xe, p–Pb) collisions at 2.76 (5.02, 5.44, 5.02) TeV in the framework of the Tsallis blast wave model with a linear transverse velocity profile and a constant velocity profile. In this model, the Tsallis temperature (T), the average radial flow velocity (⟨β⟩) and the degree of non-equilibrium (q) of the system are common for all hadrons when a combined fit is performed to the p T spectra of different particles at a given centrality. It is found that the model can describe the particle spectra well up to 3 GeV c −1. For both profiles, the transverse flow velocity decreases from central to peripheral collisions while the non-extensive parameter q exhibits the opposite behavior, indicating a more rapid expansion and reduced off-equilibrium of the system in more central collisions. Moreover, we observe that, in central collisions, ⟨β⟩ and q (T) from the fit with the linear profile are smaller (is slightly larger) than those (that) from the constant profile, while in peripheral collisions ⟨β⟩, T and q from the linear profile are compatible with those from the constant profile. We also derived and discussed the relation between the Tsallis temperature and the thermal temperature. In addition, to check whether a scenario of an early freeze-out of strange particles exists at the Large Hadron Collider, the particle spectra are investigated by grouping them into strange and non-strange hadrons. The combined fit gives an insight on the degree of non-equilibrium, the radial flow and the Tsallis temperature of the system at the kinetic decoupling. It provides a comparison between the results at different energies in the same collision system and the results in different collision systems at the same or similar energy.