Participant number fluctuations for higher moments of a multiplicity distribution

TL;DR

This paper extends the participant model to higher moments like skewness and kurtosis, revealing that participant fluctuations significantly influence high-order fluctuations in heavy-ion collisions, with implications for experimental centrality selection.

Contribution

The paper generalizes the independent participant model to include higher moments, providing a method to quantify participant number fluctuations experimentally.

Findings

Participants are not nucleons, based on SPS and LHC data.

Participant fluctuations increase with the order of fluctuation measures.

Large centrality bins at LHC are dominated by participant fluctuations.

Abstract

The independent participant model is generalized for skewness and kurtosis. The obtained relations allow to calculate the fluctuations of an arbitrarily high order. From the comparison with the SPS and the LHC data it is found that the participants are not nucleons. The contribution of the participant fluctuations increases with the order of fluctuations. The 5% centrality bins selected for the analysis at the LHC by ALICE seems to be too large. The fluctuations measures are dominated by the fluctuations of participants there. The method to quantify the value of participant number fluctuations experimentally is proposed.