Freezeout hypersurface at energies available at the CERN Large Hadron Collider from particle spectra: Flavor and centrality dependence
Abstract
We extract the freezeout hypersurface in Pb-Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=2760$ GeV at the CERN Large Hadron Collider by analyzing the data on transverse momentum spectra within a unified model for chemical and kinetic freezeout. The study is done within two schemes of freezeout: single freezeout, where all the hadrons freeze out together, versus double-freezeout, where those hadrons with nonzero strangeness content have different freezeout parameters compared to the nonstrange ones. We demonstrate that the data are better described within the latter scenario. We obtain a strange freezeout hypersurface which is smaller in volume and hotter compared to the nonstrange freezeout hypersurface for all centralities, with a reduction in ${\ensuremath{\chi}}^{2}/{N}_{\mathrm{df}}$ around $40%$. We observe from the extracted parameters that the ratio of the transverse size to the freezeout proper time is invariant under expansion from the strange to the nonstrange freezeout surfaces across all centralities. Moreover, except for the most peripheral bins, the ratio of the nonstrange-to-strange freezeout proper times is close to 1.3.