Baseline measures for net-proton distributions in high energy heavy-ion collisions

TL;DR

This paper compares net-proton distribution measurements in heavy-ion collisions to various baseline models, revealing deviations at certain energies and emphasizing the need for QCD-based comparisons to understand underlying physics.

Contribution

It systematically evaluates baseline measures for net-proton cumulants and highlights deviations at specific energies, proposing the importance of QCD calculations for accurate interpretation.

Findings

Deviations from baseline measures at 19.6 and 27 GeV energies.

Differences in proton distribution shapes cause deviations.

Highlights the need for QCD-based comparisons.

Abstract

We report a systematic comparison of the recently measured cumulants of the net-proton distributions for 0-5\% central Au+Au collisions in the first phase of the Beam Energy Scan (BES) Program at the Relativistic Heavy Collider facility to various kinds of possible baseline measures. These baseline measures correspond to assuming that the proton and anti-proton distributions, follow Poisson statistics, Binomial statistics, obtained from a transport model calculation and from a hadron resonance gas model. The higher order cumulant net-proton data corresponding to the center of mass energies ($\sqrt{s_{NN}}$) of 19.6 and 27 GeV are observed to deviate from all the baseline measures studied. The deviations are predominantly due to the difference in shape of the proton distributions between data and those obtained in the baseline measures. We also present a detailed study on the relevance of the independent production approach as a baseline for comparison with the measurements at various beam energies. Our studies points to the need for a proper comparison of the experimental measurements to QCD calculations in order to extract the exact physics process that leads to deviation of the data from the baselines presented.