Equation of State of Quark–Gluon Matter in the Clustering-of-Color-Sources Approach

Abstract

In the first few microseconds after the Big Bang, the hot dense matter was in the form of quark–gluon plasma consisting of free quarks and gluons. By colliding heavy nuclei at RHIC and LHC at a velocity close to the speed of light, we were able to recreate primordial matter and observe that matter after expansion and cooling. In the present work, we have analyzed the transverse-momentum spectra of charged particles in high-multiplicity pp collisions at LHC energies s= 5.02 and 13 TeV, published by the ALICE Collaboration, using the Color-String Percolation Model. For heavy ions, Pb–Pb at sNN= 2.76 and 5.02 TeV along with Xe–Xe at sNN= 5.44 TeV have been analyzed. The initial temperature was extracted both in low- and high-multiplicity events in pp collisions. For A−A collisions, the temperature was obtained as a function of centrality. A universal scaling in the temperature from pp and A−A collisions was obtained when multiplicity was scaled by the transverse interaction area. For the higher-multiplicity events in pp collisions at s= 5.02 and 13 TeV, the initial temperature was above the universal hadronization temperature and was consistent with the creation of deconfined matter. From the measured energy density ε and the temperature, the dimensionless quantity ε/T4 was obtained, to obtain the degree of freedom of the deconfined matter.