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This research examines how transverse momentum spectra of charged particles change with collision centrality in high-energy Pb+Pb collisions.

April 1, 2026

Centrality evolution of transverse momentum spectra of primary charged particles produced in high-energy Pb+Pb collisions at the LHC

Key Points

This research examines how transverse momentum spectra of charged particles change with collision centrality in high-energy Pb+Pb collisions.
Analyzed pT distributions using Tsallis function with transverse flow modeling.
Measured collisions at energies of 2.76 and 5.02 TeV.
Identified collision centralities and compared pT spectra across different ranges.
Transverse flow appeared at specific collision centralities between the analyzed ranges.
Kinetic freeze-out temperature significantly decreased with increasing centrality.
The q parameter showed systematic decrease with increasing collision centrality, indicating higher thermalization.

Abstract

Evolution of the experimental mid(pseudo)rapidity pT distributions of primary charged particles with changing collision centrality, measured by the ALICE Collaboration in the long pT range (up to 15 GeV/c) in Pb+Pb collisions at Formula: see text = 2.76 and 5.02 TeV, has been analyzed using thermodynamically consistent Tsallis function with embedded transverse flow. The results have been compared with the earlier results coming from simultaneous analysis of short pT range (up to 5 GeV/c) of pT spectra of the charged pions and kaons, protons and antiprotons in Pb+Pb collisions at Formula: see text=2.76 and 5.02 TeV at the LHC. Transverse flow has been absent at low Formula: see text values and it starts emerging between collision centralities (40-50)% and (30-40)% in Pb+Pb collisions at Formula: see text = 2.76 TeV and between collision centralities (50-60)% and (40-50)% in Pb+Pb collisions at Formula: see text = 5.02 TeV. Kinetic freeze-out temperature, T 0 , has decreased greatly between collision centralities (40-50)% and (30-40)% in Pb+Pb collisions at Formula: see text = 2.76 TeV and between collision centralities (50-60)% and (40-50)% in Pb+Pb collisions at Formula: see text = 5.02 TeV. We have estimated border value of collision centrality for crossover phase transition from the dense hadronic state to that of QGP state (or mixed state of QGP and hadrons) to be Formula: see text = 109 ± 8 and Formula: see text = Formula: see text in Pb+Pb collisions at Formula: see text = 2.76 and 5.02 TeV, respectively. Non-extensivity parameter q has decreased systematically with increasing Formula: see text and Formula: see text (with an increase in collision centrality) in both Pb+Pb collisions at Formula: see text = 2.76 and 5.02 TeV. This denotes systematic increase in degree of system thermalization with increasing centrality of Pb+Pb collisions at Formula: see text = 2.76 and 5.02 TeV at the LHC, in agreement with similar result of previous works. Strong negative correlation has been obtained between parameter q and Formula: see text as well as between parameter q and Formula: see text with Pearson correlation coefficient R(x,y) ~ −1 in both Pb+Pb collisions at Formula: see text = 2.76 and 5.02 TeV. Kinetic freeze-out temperature parameter, T 0 , has proved to be strongly anticorrelated with average transverse flow velocity, Formula: see text, with R(Formula: see text, Formula: see text) ~ −1 in both Pb+Pb collisions at Formula: see text = 2.76 and 5.02 TeV, in agreement with analogous result of earlier works. The obtained results have been compared with those extracted in minimum bias p+p and p+Pb collisions at Formula: see text = 2.76 and 5.02 TeV.

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