Baryon Stopping as a Probe of Deconfinement Onset in Relativistic Heavy-Ion Collisions

TL;DR

This paper proposes that irregularities in baryon stopping during heavy-ion collisions indicate a phase transition in the nuclear matter, with model calculations showing distinct signatures for different equations of state.

Contribution

It introduces a novel method to identify the deconfinement phase transition through baryon stopping irregularities in collision experiments.

Findings

First-order phase transition predicts strong irregularity in net-proton rapidity distributions.

Hadronic EoS shows smooth evolution with no irregularity.

Preliminary experimental data suggest similar irregularity trends.

Abstract

It is argued that an irregularity in the baryon stopping is a natural consequence of a phase transition occurring in the compression stage of a nuclear collision. It is a combined effect of the softest point inherent in an equation of state (EoS) with a phase transition and a change in the nonequilibrium dynamics from hadronic to partonic transport. Thus, this irregularity is a signal from a hot and dense stage of the nuclear collision. In order to illustrate this proposition, calculations within the three-fluid model were performed with three different EoS's: a purely hadronic EoS, an EoS with a first-order phase transition and that with a smooth crossover transition. It is found that predictions within the first-order-transition scenario indeed reveal an a strong irregularity in the incident energy dependence of the form of the net-proton rapidity distributions in central collisions. This behavior is in contrast to that for the hadronic scenario, where the distribution form gradually evolve, displaying no irregularity. The case of the crossover EoS is intermediate. Only a weak irregularity takes place. Experimental data also exhibit a trend of similar irregularity, which is however based on still preliminary data at energies of 20A GeV and 30A GeV.