Geometric scaling in symmetric nucleus-nucleus collisions

TL;DR

This paper demonstrates a geometric scaling law in nucleus-nucleus collisions at the LHC, showing that multiplicity dependence on impact parameter is consistent across different collision systems when properly defined.

Contribution

It introduces a new impact parameter-based centrality definition and an inversion method to reconstruct multiplicity dependence from experimental data, improving upon traditional Monte Carlo Glauber models.

Findings

Impact parameter-based centrality aligns multiplicity data across systems

Reconstructed impact parameter dependence matches experimental data better

Provides a new method for analyzing collision geometry

Abstract

We show that the centrality dependence of the multiplicity is identical in Pb+Pb and Xe+Xe collisions at the LHC, up to a constant factor. This geometric scaling is revealed if one defines centrality according to impact parameter, as opposed to the usual experimental definition, which is in terms of multiplicity. We reconstruct the impact parameter dependence of the multiplicity from experimental data using a recently-developed inversion method, which turns out to describe ALICE Xe+Xe multiplicity data much better than usual Monte Carlo Glauber fits. The multiplicity as function of impact parameter extracted from ALICE data is compared to model calculations.