The Parton-Hadron Phase Transition in Central Nuclear Collisions at the CERN SPS

TL;DR

This paper analyzes Pb+Pb collisions at CERN SPS energy, suggesting the formation of a partonic state that undergoes a phase transition to hadrons, with evidence of high energy density and expansion in heavy-ion collisions.

Contribution

It provides evidence for a partonic phase in central Pb+Pb collisions and describes the hadronization process at specific temperatures, extending the understanding of quark-gluon plasma formation.

Findings

Partonic state formed in central Pb+Pb collisions

Hadronization occurs around T = 185 MeV

Energy density increases with collision system mass

Abstract

A selection of recent data referring to Pb+Pb collisions at the SPS CERN energy of 158 GeV per nucleon is presented which might describe the state of highly excited strongly interacting matter both above and below the deconfinement to hadronization (phase) transition predicted by lattice QCD. A tentative picture emerges in which a partonic state is indeed formed in central Pb+Pb collisions which hadronizes at about T = 185 MeV, and expands its volume more than tenfold, cooling to about 120 MeV before hadronic collisions cease. We suggest further that all SPS collisions, from central S+S onward, reach that partonic phase, the maximum energy density increasing with more massive collision systems.