Percolation and de-confinement in relativistic nuclear collisions

Abstract

In the present work we have analyzed the transverse momentum spectra of charged particles in high multiplicity $pp$ collisions at LHC energies $\sqrt{s}$ = 5.02 and 13 TeV using the Color String Percolation Model (CSPM). For heavy ions $Pb-Pb$ at $\sqrt{s_{NN}}$ = 2.76 and 5.02 TeV along with $Xe-Xe$ at $\sqrt{s_{NN}}$= 5.44 TeV have been analyzed. The initial temperature is extracted both in low and high multiplicity events in $pp$ collisions. For $A-A$ collisions the temperature is obtained as a function of centrality. From the measured energy density $\epsilon$ and the temperature T the dimensionless quantity $\epsilon /T^4$ is obtained. Our results for Pb-Pb and Xe-Xe collisions show a sharp increase in $\epsilon /T^4$ above T $\sim$ 210 MeV and reaching the ideal gas of quarks and gluons value of $\epsilon /T^4\sim$ 16 at temperature $\sim$ 230 MeV. At this temperature there is a transition from the fluid behavior of QCD matter strongly interacting to a quasi free gas of quarks and gluons.

Presented at the 53rd International Symposium on Multiparticle Dynamics, 21-26 September, 2025, Corfu, Greece