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.
Highlights
Measurements of the number of particles produced in the final states of high-energy hadron-nucleus (p-A) collisions have opened new windows in the study of dense partonic systems
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 work in the theoretical framework of high-energy quantum chromodynamics (QCD), and, following the picture of particle production introduced in Refs. [20,21], we argue that the multiplicity of particles probed around some off-forward rapidity in the region of fragmentation of the hadrons reflects, in each event, the integrated gluon density in the corresponding realization of the Fock state of the hadron at the time of interaction
Summary
Measurements of the number of particles produced in the final states of high-energy hadron-nucleus (p-A) collisions have opened new windows in the study of dense partonic systems. Collisions at the LHC, which will require us to introduce some amount of modelization for the evolution of the proton, we focus on the simpler case of onium-nucleus collisions, where one can gain a very solid theoretical understanding in controlled asymptotic limits that allow to study multiplicity fluctuations analytically. To this purpose, we shall work within the color dipole model (supplemented with an infrared cutoff for parton confinement), whose formulation is well suited to address this problem. Technical details on the numerical calculations are gathered in the Appendices
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