Bose enhancement, the Liouville effective action and the high multiplicity tail in p-A collisions

TL;DR

This paper investigates particle multiplicity fluctuations in proton-nucleus collisions within the dense-dilute CGC framework, highlighting Bose enhancement effects, the Liouville effective action, and resulting probability distributions.

Contribution

It introduces a novel calculation of multiplicity fluctuations driven by Bose enhancement, linking it to the Liouville effective action and providing explicit probability distributions.

Findings

Bose enhancement is the dominant source of fluctuations in p-A collisions.

The multiplicity distribution closely follows a gamma distribution.

Pairwise HBT correlations provide first-order corrections to the distribution.

Abstract

In the framework of dense-dilute CGC approach we study fluctuations in the multiplicity of produced particles in p-A collisions. We show that the leading effect that drives the fluctuations is the Bose enhancement of gluons in the proton wave function. We explicitly calculate the moment generating function that resums the effects of Bose enhancement. We show that it can be understood in terms of the Liouville effective action for the composite field which is identified with the fluctuating density, or saturation momentum of the proton. The resulting probability distribution turns out to be very close to the gamma-distribution. We also calculate the first correction to this distribution which is due to pairwise Hanbury Brown-Twiss correlations of produced gluons.