Features of hadronic and deconfined matter in a range of collision energies spanning from the BNL Alternating Gradient Synchrotron to the CERN Large Hadron Collider

Abstract

Previous extensive studies on the dependence of the average transverse momentum, its slope as a function of the hadron mass, and the average transverse expansion on the particle multiplicity per unit rapidity and unit transverse overlap area of the colliding partners are extended to the ratio of the energy density to the entropy density. The behavior of the ratio between the average transverse momentum and the square root of the particle multiplicity per unit rapidity and unit transverse overlap area $\ensuremath{\langle}{p}_{T}\ensuremath{\rangle}/\sqrt{\ensuremath{\langle}dN/dy\ensuremath{\rangle}/{S}_{\ensuremath{\perp}}}$ as a function of collision energy for a given centrality or as a function of centrality for a given collision energy supports the predictions of color glass condensate and percolation based approaches. The dependence of the ratio of the energy density $\ensuremath{\langle}d{E}_{T}/dy\ensuremath{\rangle}/{S}_{\ensuremath{\perp}}$ to the entropy density $\ensuremath{\langle}dN/dy\ensuremath{\rangle}/{S}_{\ensuremath{\perp}}$ at different collision centralities for $A\text{\ensuremath{-}}A$ collisions from the Alternating Gradient Synchrotron, the Super Proton Synchrotron, the BNL Relativistic Heavy Ion Collider, and the CERN Large Hadron Collider energies is presented. The trend of this ratio towards a plateau at the highest RHIC energies followed by a steep rise at LHC energies is in agreement with theoretical predictions made 40 years ago that indicate this behavior as a signature of a phase transition. This pattern strongly depends on the collision geometry, converging towards the dependence that characterizes the $pp$ minimum bias collisions for the most peripheral $A\text{\ensuremath{-}}A$ collisions. Expected similarities between $pp$ and Pb-Pb collisions at LHC energies are confirmed.