Near-threshold heavy quarkonium photoproduction in a light-front spectator model

The near-threshold photo- and electroproduction of heavy vector quarkonia off the proton provides direct access to its gluonic structure. In particular, the cross section for J / Ψ photoproduction near threshold is governed by the proton’s gluon gravitational form factors (GFFs). In this work, we employ the leading-order generalized parton distribution framework, together with gluon GFFs calculated in a light-front gluon-spectator model inspired by soft-wall AdS/QCD to predict both the differential and total cross sections for near-threshold J / Ψ and ϒ photoproduction. Our results for J / ψ photoproduction show good agreement with the low-momentum-transfer data from the J / ψ − 007 experiment and the GlueX Collaboration at Jefferson Lab. However, at large momentum transfer, the next-to-leading order QCD effects are necessary to describe the data.