Correcting event-by-event fluctuations in heavy-ion collisions for exact global conservation laws with the generalized subensemble acceptance method

TL;DR

The paper introduces SAM-2.0, a method to accurately correct cumulants of fluctuations in heavy-ion collisions for global conservation laws, enhancing the comparison between experimental data and theoretical models.

Contribution

SAM-2.0 extends the original method to non-uniform systems and momentum space acceptances, improving fluctuation analysis in heavy-ion collision experiments.

Findings

Provides a formalism for correction of cumulants considering global conservation laws.

Applicable to various collision energies and momentum space acceptances.

Bridges the gap between experimental measurements and theoretical calculations.

Abstract

We introduce the subensemble acceptance method 2.0 (SAM-2.0) -- a procedure to correct cumulants of a random number distribution inside a subsystem for the effect of exact global conservation of a conserved quantity to which this number is correlated, with applications to measurements of event-by-event fluctuations in heavy-ion collisions. The method expresses the corrected cumulants in terms of the cumulants inside and outside the subsystem that are not subject to the exact conservation. The derivation assumes that all probability distributions associated with the cumulants are peaked at the mean values but are otherwise of arbitrary shape. The formalism reduces to the original SAM [V. Vovchenko et al., Phys.Lett.B 811 (2020) 135868 [arXiv:2003.13905]] when applied to a coordinate space subvolume of a uniform thermal system. As the new method is restricted neither to the uniform systems nor to the coordinate space, it is applicable to fluctuations measured in heavy-ion collisions at various collision energies in different momentum space acceptances. The SAM-2.0 thus brings the experimental measurements and theoretical calculations of event-by-event fluctuations closer together, as the latter are typically performed without the account of exact global conservation.