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The near threshold photo or electroproduction of heavy vector quarkonium offthe proton is studied in quantum chromodynamics. Similar to the high-energylimit, the production amplitude can be factorized in terms of gluonicGeneralized Parton Distributions and the quarkonium distribution amplitude. Atthe threshold, the threshold kinematics has a large skewness parameter $\xi$,leading to the dominance of the spin-2 contribution over higher-spin twist-2operators. Thus threshold production data are useful to extract the gluonicgravitational form factors, allowing studying the gluonic contributions to thequantum anomalous energy, mass radius, spin and mechanical pressure in theproton. We use the recent GlueX data on the $J/\psi$ photoproduction toillustrate the potential physics impact from the high-precision data fromfuture JLab 12 GeV and EIC physics program.

QCD Analysis of Near-Threshold Photon-Proton Production of Heavy Quarkonium