Analysis of Midrapidity p[sub.T] Distributions of Identified Charged Particles in Pb + Pb Collisions at [square root of s[sub.nn]] = 5.02 TeV Using Tsallis Distribution with Embedded Transverse Flow

The midrapidity transverse momentum distributions of the charged pions, kaons, protons, and antiprotons, measured by ALICE Collaboration at ten centrality classes of Pb + Pb collisions at [square root of s[sub.nn] ] = 5.02 TeV in the Large Hadron Collider (LHC, CERN, Switzerland), are successfully analyzed using combined minimum χ[sup.2] fits with a thermodynamically non-consistent, as well as thermodynamically consistent, Tsallis function with transverse flow. The extracted non-extensivity parameter q decreases systematically for all considered particle species with increasing Pb + Pb collision centrality, suggesting an increase in the degree of system thermalization with an increase in collision centrality. The results for q suggest quite a large degree of thermalization of quark-gluon plasma (QGP) created in central Pb + Pb collisions at [square root of s[sub.nn] ]= 5.02 TeV with the average number of participant nucleons 〈N[sub.part] 〉 > 160. The obtained significantly different growth rates of transverse flow velocity, 〈β[sub.T] 〉, in regions 〈N[sub.part] 〉 < 71 ± 7 and 〈N[sub.part] 〉 > 71 ± 7 with the temperature parameter T[sub.0] remaining constant within uncertainties in region 〈N[sub.part] 〉 > 71 ± 7 probably indicates that 〈N[sub.part] 〉 ≈ 71 ± 7 (corresponding to 〈dN[sub.ch] /dη〉 ≈ 251 ± 20) is a threshold border value for a crossover transition from a dense hadronic state to the QGP phase (or mixed phase of QGP and hadrons) in Pb + Pb collisions at [square root of s[sub.nn] ] = 5.02 TeV. The threshold border value for transverse flow velocity 〈β[sub.T] 〉 ≈ 0.46 ± 0.03 (corresponding to 〈N[sub.part] 〉 ≈ 71 ± 7), estimated by us in Pb + Pb collisions at [square root of s[sub.nn] ] = 5.02 TeV, agrees well with the corresponding border value 〈β[sub.T] 〉 ≈ 0.44 ± 0.02, recently obtained in Xe + Xe collisions at [square root of s[sub.nn] ]= 5.44 TeV, and with almost constant 〈β[sub.T] 〉 values extracted earlier in the Beam Energy Scan (BES) program of the Relativistic Heavy-Ion Collider (RHIC, Brookhaven, GA, USA) in central Au + Au collisions in the [square root of s[sub.nn] ]= 7.7 − 39 GeV energy range, where the threshold for QGP production is achieved. The correlations between extracted T[sub.0] and 〈β[sub.T] 〉 parameters are found to be greatly different in regions 〈β[sub.T] 〉 < 0.46 and 〈β[sub.T] 〉 > 0.46, which further supports our result obtained for the threshold border value in Pb + Pb collisions at [square root of s[sub.nn] ]= 5.02 TeV.