Constraining the proton transverse partonic distribution through coherent diffractive $J/\psi$ production at HERA within a static Gaussian hot spot model

TL;DR

This study models the proton's transverse parton distribution using a static Gaussian hot spot approach, analyzing how geometric configurations influence the t-dependence of coherent J/psi production at HERA.

Contribution

It introduces a simple geometric hot spot model with adjustable parameters to describe the proton's transverse structure in small-x regime.

Findings

Geometric variations significantly affect the t-slope of the cross section.

Rotational degrees of freedom impact the cross section at higher t values.

Small-t region remains insensitive to geometric variations.

Abstract

We investigate the transverse parton distribution of the proton through the t-dependence of the coherent J/psi differential cross section extracted from HERA measurements in the small-x regime. Employing a simple static Gaussian hot spot model inspired by the large-x three-valence-quark picture of the proton, we introduce three geometric degrees of freedom of each hot spot: the Gaussian width of each hot spot, the spatial distance of the valence quarks from the proton center, and their azimuthal orientation. In the simplest implementation, the valence quarks are assumed to form a symmetric triangular configuration. We find that variations in these geometric structures significantly influence the t-slope of the coherent cross section. In particular, the rotational degree of freedom strongly affects the cross section at t > 0.5 GeV^2, while the small-t region remains largely insensitive to variations in this parameter.