Formation of deuterons by coalescence: Consequences on the deuteron number fluctuations

TL;DR

This paper investigates whether deuterons are formed directly from a thermal source or through coalescence of nucleons by analyzing fluctuations in deuteron numbers, providing a method to distinguish the two mechanisms.

Contribution

It introduces an event-by-event fluctuation analysis to differentiate cluster formation mechanisms, predicting measurable deviations in deuteron number fluctuations.

Findings

Poisson fluctuations indicate thermal emission.

Deviations from Poisson suggest coalescence.

Predicted variance and kurtosis differences are testable.

Abstract

Two scenarios for cluster production have since long been discussed in the literature: i) direct emission of the clusters from a (grand canonical) thermal source or ii) subsequent formation of the clusters by coalescence of single nucleons. While both approaches have been successfully applied in the past it has not yet been clarified which of the two mechanisms dominates the cluster production. We propose to use recently developed event-by-event techniques to study particle multiplicity fluctuations on nuclear clusters and employ this analysis to the deuteron number fluctuations to disentangle the two production mechanisms. We argue that for a grand canonical cluster formation, the cluster fluctuations will follow Poisson distribution, while for the coalescence scenario, the fluctuations will strongly deviate from the Poisson expectation. We estimate the effect to be 10% for the variance and up to a factor of 5 for the kurtosis of the deuteron number multiplicity distribution. Our prediction can be tested in the beam energy scan program at RHIC as well as experiments at the FAIR and NICA facilities.