DIS and the effects of fluctuations: a momentum space analysis

TL;DR

This paper analyzes a momentum space dipole model for deep inelastic scattering, comparing it with HERA data, and investigates the impact of gluon fluctuations, concluding they are not significant at HERA energies.

Contribution

It introduces a momentum space parametrization of the dipole amplitude that interpolates between saturation and perturbative regimes, and assesses gluon fluctuations in DIS.

Findings

Gluon fluctuations are not observed at HERA energies.

The model fits HERA data well across different regimes.

Fluctuations beyond mean-field are negligible in the analyzed energy range.

Abstract

Among the dipole models of deep inelastic scattering at small values of the Bjorken variable $x$, one has been recently proposed which relates the virtual photon-proton cross section to the dipole-proton forward scattering amplitude in momentum space. The latter is parametrized by an expression which interpolates between its behavior at saturation and the travelling wave, ultraviolet, amplitudes predicted by perturbative QCD from the Balitsky-Kovchegov equation. Inspired by recent developments in coordinate space, we use this model to parametrize the proton structure function and confront it to HERA data on $ep$ deep inelastic scattering. Both event-by-event and the physical amplitudes are considered, the latter used to investigate the effect of gluon number fluctuations, beyond the mean-field approximation. We conclude that fluctuations are not present in DIS at HERA energies.