Abstract
The near threshold photo or electroproduction of heavy vector quarkonium off the proton is studied in quantum chromodynamics. Similar to the high-energy limit, the production amplitude can be factorized in terms of gluonic Generalized Parton Distributions and the quarkonium distribution amplitude. At the threshold, the threshold kinematics has a large skewness parameter $\xi$, leading to the dominance of the spin-2 contribution over higher-spin twist-2 operators. Thus threshold production data are useful to extract the gluonic gravitational form factors, allowing studying the gluonic contributions to the quantum anomalous energy, mass radius, spin and mechanical pressure in the proton. We use the recent GlueX data on the $J/\psi$ photoproduction to illustrate the potential physics impact from the high-precision data from future JLab 12 GeV and EIC physics program.
Highlights
There has been rising interest in measuring the photoproduction of J=ψ particles near the threshold
Similar to the high-energy limit, the production amplitude can be factorized in terms of gluonic generalized parton distributions and the quarkonium distribution amplitude
In the vector dominance model [2,3,7], the vector-meson photoproduction is related to the forward meson-nucleon scattering where a direct operator product expansion (OPE) in terms of gluonic matrix elements is applicable [8,9,10,11]
Summary
There has been rising interest in measuring the photoproduction of J=ψ particles near the threshold. In the vector dominance model [2,3,7], the vector-meson photoproduction is related to the forward meson-nucleon scattering where a direct operator product expansion (OPE) in terms of gluonic matrix elements is applicable [8,9,10,11] This process has been approached using dispersive analysis [12,13] and holographic QCD [14,15,16,17].
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