Constraining the proton transverse partonic distribution through coherent diffractive <i>J</i> /ψ production at HERA within a static Gaussian hot spot model

We investigate the transverse parton distribution of the proton through the t-dependence of the coherent J/ψ 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: (1) the Gaussian width of each hot spot, (2) the spatial distance of the valence quarks from the proton center, and (3) 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 &gt; 0.5 GeV 2 , while the small-t region remains largely insensitive to variations in this parameter.