Analysis of Midrapidity pT Distributions of Identified Charged Particles in Pb + Pb Collisions at snn = 5.02 TeV Using Tsallis Distribution with Embedded Transverse Flow

Abstract

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 = 5.02 TeV in the Large Hadron Collider (LHC, CERN, Switzerland), are successfully analyzed using combined minimum χ2 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 = 5.02 TeV with the average number of participant nucleons > 160. The obtained significantly different growth rates of transverse flow velocity, , in regions < 71 ± 7 and > 71 ± 7 with the temperature parameter T0 remaining constant within uncertainties in region > 71 ± 7 probably indicates that ≈ 71 ± 7 (corresponding to ≈ 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 = 5.02 TeV. The threshold border value for transverse flow velocity ≈ 0.46 ± 0.03 (corresponding to ≈ 71 ± 7), estimated by us in Pb + Pb collisions at = 5.02 TeV, agrees well with the corresponding border value ≈ 0.44 ± 0.02, recently obtained in Xe + Xe collisions at = 5.44 TeV, and with almost constant values extracted earlier in the Beam Energy Scan (BES) program of the Relativistic Heavy-Ion Collider (RHIC, Brookhaven, USA) in central Au + Au collisions in the = 7.7 − 39 GeV energy range, where the threshold for QGP production is achieved. The correlations between extracted T0 and parameters are found to be greatly different in regions < 0.46 and > 0.46, which further supports our result obtained for the threshold border value in Pb + Pb collisions at = 5.02 TeV.

Simultaneous Analysis of Midrapidity pT Spectra of Identified Particle Species in Pb + Pb Collisions at snn = 2.76 TeV Using Tsallis Distribution with Transverse Flow

“…This study continues from our recent papers [17][18][19]33] devoted to analysis, applying simultaneous theoretical model fits, of the centrality dependencies of transverse momentum spectra of the charged pions, kaons, protons, and antiprotons produced in high-energy proton-proton, Xe + Xe, and Pb + Pb collisions at the LHC, measured by ALICE Collaboration. Since the pions, kaons, and (anti)protons represent the largest predominant part of the final particles coming from high-energy proton-proton and heavy-ion collisions, we believe that the simultaneous analysis of these particle species can reveal the collective properties of the system produced in these collisions.…”

“…The chemical freeze-out parameters, such as the temperature T ch and the baryochemical potential µ b at the moment of chemical freeze-out are extracted by performing fits of the particle abundancies and their ratios with the thermal, statistical hadronization models [10][11][12][13][14][15]. The kinetic freeze-out parameters, such as the transverse flow velocity and the corresponding temperature at the moment of kinetic freeze-out, are obtained [10,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] from fitting the transverse momentum (p T ) distributions of particles with the help of various theoretical and phenomenological model functions, including the hydro-inspired blast-wave models.…”

“…For the description of the p T spectra of particles in high-energy heavy-ion collisions, different transverse expansion models are embedded into Tsallis statistics. To extract the kinetic freeze-out temperature and transverse flow velocity, different model functions have been used [10,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]: the Blast-Wave model with Boltzmann-Gibbs statistics (the BGBW model), the Blast-Wave model with Tsallis statistics (the TBW model), the improved Tsallis distribution with flow effect, Hagedorn formula with the embedded transverse flow, and recently [18,33], the Tsallis distribution function with included transverse flow.…”

“…In Refs. [18,33] we studied the dependencies of midrapidity p T spectra of the charged pions, kaons, protons, and antiprotons, measured by ALICE Collaboration, on the average number of participant nucleons, N part , in Xe+Xe collisions at √ s nn = 5.44 TeV and Pb + Pb collisions at √ s nn = 5.02 TeV, respectively. The combined minimum χ 2 fits with thermodynamically consistent and non-consistent Tsallis function with embedded transverse flow could describe quite well the p T distributions of the studied particle species in various collision centralities, defined by N part , in Xe + Xe and Pb + Pb collisions at √ s nn = 5.44 TeV and 5.02 TeV, respectively.…”

“…The combined minimum χ 2 fits with thermodynamically consistent and non-consistent Tsallis function with embedded transverse flow could describe quite well the p T distributions of the studied particle species in various collision centralities, defined by N part , in Xe + Xe and Pb + Pb collisions at √ s nn = 5.44 TeV and 5.02 TeV, respectively. From the analysis of the N part dependencies of the extracted kinetic freeze-out temperature, T 0 , and average transverse flow velocity, β T , it was deduced that N part ≈ 44 ± 5 [18] and N part ≈ 71 ± 7 [33] could be the threshold border values of collision centrality for a crossover transition from a dense hadronic state to the QGP phase (or mixed phase of QGP and hadrons) in Xe + Xe and Pb + Pb collisions at √ s nn = 5.44 TeV and 5.02 TeV, respectively.…”