Gluon density fluctuations in dilute hadrons

Abstract

Motivated by the relation existing between the gluon density in a hadron and the multiplicity of the particles measured in the final state of hadron-nucleus collisions, we study systematically the fluctuations of the gluon density in onia, which are the simplest dilute hadrons, of different sizes and at various rapidities. We argue that the small and the large-multiplicity tails of the gluon distributions present universal features, which should translate into properties of the multiplicity of the particles measured in the final state of high-energy proton-nucleus collisions, or of deep-inelastic scattering at a future electron-ion collider. We propose simple physical pictures of the rare events populating the tails of the multiplicity distribution that allow us to derive analytical formulas describing these universal behaviors, and we compare them to the results of Monte Carlo simulations.