Geometrical scaling description for the exclusive production of vector mesons and deeply virtual Compton scattering

TL;DR

This paper demonstrates that the cross sections for exclusive vector meson production and DVCS can be universally described by geometric scaling, unifying data across different processes and energies in saturation physics.

Contribution

It introduces a universal scaling law for exclusive vector meson and DVCS production, applicable to photon-proton and photon-nucleus interactions, based on the saturation scale Q_s.

Findings

Successfully describes all available DESY-HERA data for vector mesons and DVCS

Derives a universal expression for cross sections using geometric scaling

Discusses nuclear shadowing effects in photon-nucleus interactions

Abstract

In this work, we investigate the exclusive production of particles in scattering processes in the so-called saturation region. Within this scheme the phenomenon of geometric scaling takes place: cross sections are functions only of a dimensionless combination of the relevant kinematic variables, which happens both in inclusive and diffractive cases, as in the production of vector mesons. In particular, the scaling variable is given in general by $\tau = Q^2/Q_s^2$, where $Q^2$ is the photon virtuality and $Q_s$ represents the saturation scale, which drives the energy dependence and the corresponding nuclear effects. Based on the scaling property, we are able to derive a universal expression for the cross sections for the exclusive vector meson production and deeply virtual Compton scattering (DVCS) in both photon-proton and photon-nucleus interactions. This phenomenological result describes all available data from DESY-HERA for $\rho$, $\phi$ and $J/\psi$ production and DVCS measurements. A discussion is also carried out on the size of nuclear shadowing corrections on photon-nucleus interaction.