A Centrality-independent Framework for Revealing Genuine Higher-Order Cumulants in Heavy-Ion Collisions

TL;DR

This paper introduces a new centrality-independent method for analyzing higher-order cumulants in heavy-ion collisions, effectively removing volume fluctuation effects and enabling more accurate probing of the medium's thermodynamic properties.

Contribution

The authors develop a novel cumulant analysis framework using Edgeworth expansion and optimization algorithms, independent of traditional centrality measures, validated with UrQMD simulations.

Findings

Method accurately reproduces cumulant patterns similar to $N_{\text{part}}$-based centrality.

Eliminates reliance on conventional centrality definitions.

Enables extraction of genuine physical signals from event-by-event fluctuations.

Abstract

We propose a novel centrality definition-independent method for analyzing higher-order cumulants, specifically addressing the challenge of volume fluctuations that dominate in low-energy heavy-ion collisions. This method reconstructs particle number distributions using the Edgeworth expansion, with parameters optimized via a combination of differential evolution algorithm and Bayesian inference. Its effectiveness is validated using UrQMD model simulations and benchmarked against traditional approaches, including centrality definitions based on particle multiplicity. Our results show that the proposed framework yields cumulant patterns consistent with those obtained using number of participant nucleon ($N_{\text{part}}$) based centrality observables, while eliminating the conventional reliance on centrality determination. This consistency confirms the method's ability to extract genuine physical signals, thereby paving the way for probing the intrinsic thermodynamic properties of the produced medium through event-by-event fluctuations.