Robustness of the Baryon-Stopping Signal for the Onset of Deconfinement in Relativistic Heavy-Ion Collisions

TL;DR

This study shows that the irregularity in baryon stopping signals, indicative of the onset of deconfinement in heavy-ion collisions, remains robust even with limited experimental acceptance, but careful consistency in measurement conditions is essential.

Contribution

It demonstrates the robustness of the baryon-stopping irregularity signal against acceptance limitations and highlights the importance of consistent measurement conditions across energies.

Findings

The wiggle in the excitation function of $C_y$ is a robust signal of a first-order phase transition.

Acceptance cuts significantly influence the distinguishability of hadronic and crossover scenarios.

Consistent measurement acceptance is crucial for reliable interpretation of the baryon stopping signal.

Abstract

The impact of the experimental acceptance, i.e. transverse-momentum ($p_T$) cut-off and limited rapidity region, on the earlier predicted irregularity in the excitation function of the baryon stopping is studied. This irregularity is a consequence of the onset of deconfinement occurring in the compression stage of a nuclear collision and manifests itself as a wiggle in the excitation function of the reduced curvature ($C_y$) of the net-proton rapidity distribution at midrapidity. It is demonstrated that the wiggle is a very robust signal of a first-order phase transition that survives even under conditions of a very limited acceptance. At the same time the $C_y$ for pure hadronic and crossover transition scenarios become hardly distinguishable, if the acceptance cuts off too much of the low-$p_T$ proton spectrum and/or puts too narrow rapidity window around midrapidity. It is found that the shape of the net-proton rapidity distribution near midrapidity depends on the $p_T$ cut-off. This implies that the measurements should be taken at the same acceptance for all collision energies in order to reliably conclude on the presence or absence of the irregularity.