Centrality dependence of kinetic freeze-out parameters with fixed and variable flow profile in Au-Au collisions at 62.4 and 200 GeV

Using data from the STAR Collaboration at RHIC, we analyze the transverse momentum (pT) spectra of the deuteron (d), anti-deuteron (d¯), and triton (t) generated in Au-Au collisions at center of mass energy (sNN)=62.4 and 200 GeV. We extract the mean transverse momentum (⟨pT⟩), transverse flow velocity (βT), and kinetic freeze-out temperature (T0) for multiple centrality intervals using the blast wave model with Boltzmann–Gibbs statistics. According to our observations, T0 and βT rise with collision energy, stating higher thermal energy at 200 GeV and stronger collective flow. Paradoxical variations can be seen in the centrality dependence of T0: When n0 is fixed, it grows from central to peripheral collisions, implying a shorter fireball lifetime in peripheral collisions; when n0 is treated as a free parameter, it drops, which is consistent with a higher initial energy density in central collisions. Besides that, from central to peripheral collisions, βT and ⟨pT⟩ consistently decrease. Due to the improved coalescence efficiency, the ⟨pT⟩ of d and d¯ is larger at 200 GeV, whereas the ⟨pT⟩ of t is larger at 62.4 GeV, suggesting less favorable conditions for t formation at higher energies. These findings show how collision energy, centrality, and particle mass interact complexly to determine collective behavior and freeze-out dynamics in heavy-ion collisions.