Features of hadronic and deconfined matter from AGS to LHC energies

TL;DR

This paper investigates the behavior of energy density to entropy density ratios in high-energy nuclear collisions, providing evidence supporting phase transition signatures and comparing different collision systems from AGS to LHC energies.

Contribution

It extends previous studies by analyzing the energy density to entropy density ratio across various energies and centralities, confirming theoretical predictions of phase transition signatures.

Findings

Ratio of energy density to entropy density shows a plateau at RHIC energies and rises at LHC energies.

Behavior supports CGC and percolation models of particle production.

Similarities between pp and Pb-Pb collisions at LHC energies are observed.

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 behaviour of the ratio between the average transverse momentum and the square root of the particle multiplicity per unit rapidity and unit transverse overlap area $\langle p_T \rangle/\sqrt{\langle dN/dy\rangle/S_{\perp}}$ 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 CGC and percolation based approaches. The dependence of the ratio of the energy density $\langle dE_{T}/dy\rangle/S_{\perp}$ to the entropy density $\langle dN/dy\rangle/S_{\perp}$ at different collision centralities for A-A collisions from AGS, SPS, RHIC and LHC 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 behaviour 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 (MB) collisions for the most peripheral A-A collisions. Expected similarities between pp and Pb-Pb collisions at LHC energies are confirmed.