On the effect of secondary protons on baryon and proton number cumulants in event-by-event analysis

TL;DR

This paper analyzes how secondary protons affect the measurement of higher order cumulants of proton and baryon numbers in heavy ion collisions, proposing a simple correction method to improve the accuracy of thermodynamic property studies.

Contribution

It introduces a simple formula to account for and remove the background effect of secondary protons from cumulant measurements in event-by-event analyses.

Findings

Secondary protons constitute about 20% of observed protons at STAR.

The background effect significantly influences the third-order cumulant.

Removing this effect is essential for accurate thermodynamic analysis.

Abstract

We investigate the effects of secondary (knockout) protons, which constitute about 20% of the observed protons at STAR, on the higher order cumulants of proton and baryon numbers measured by event-by-event analyses in relativistic heavy ion collisions. We argue that the contribution of this background effect on the cumulants is expressed by a simple formula, and that hence their effects can be removed in the experimental analysis. It is discussed that this background effect has non-negligible contribution to recently observed proton number cumulants at STAR, especially the third-order one, and that the removal of this effect is crucial to investigate the thermodynamical properties of the primordial hot medium appropriately.