Higher order net-proton number cumulants dependence on the centrality definition and other spurious effects

TL;DR

This paper investigates how the choice of centrality definition and other experimental effects influence higher order net-proton cumulants in relativistic nuclear collisions, highlighting systematic uncertainties and the impact of event pile-up.

Contribution

It demonstrates the significant dependence of net-proton cumulant ratios on centrality definitions and quantifies the effects of pile-up and other spurious factors using the UrQMD model.

Findings

Centrality definition greatly affects cumulant ratios.

Finite efficiency introduces systematic uncertainties.

Event pile-up and double counting impact higher order cumulants.

Abstract

We study the dependence of the normalized moments of the net-proton multiplicity distributions on the definition of centrality in relativistic nuclear collisions at a beam energy of $\sqrt{s_{\mathrm{NN}}}= 7.7$ GeV. Using the UrQMD model as event generator we find that the centrality definition has a large effect on the extracted cumulant ratios. Furthermore we find that the finite efficiency for the determination of the centrality introduces an additional systematic uncertainty. Finally, we quantitatively investigate the effects of event-pile up and other possible spurious effects which may change the measured proton number. We find that pile-up alone is not sufficient to describe the data and show that a random double counting of events, adding significantly to the measured proton number, affects mainly the higher order cumulants in most central collisions.