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

In the framework of the dense-dilute color glass condensate 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 γ distribution. We also calculate the first correction to this distribution, which is due to pairwise Hanbury Brown–Twiss correlations of produced gluons.