Theory seminar - Feng Yuan

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Speaker: Feng Yuan (LBNL)

Title: Near Threshold Heavy Quarkonium Photoproduction

Abstract: There has been a claim in the literature that the near threshold photo-production of heavy quarkonium can measure the gravitational form factors and hence to directly measure the proton mass distribution. In this talk, we will present our recent analysis based on perturbative QCD calculations for this process at large momentum transfer. We take into account the contributions from the leading three-quark Fock states of the nucleon. The dominant contribution comes from the three-quark Fock state with one unit quark orbital angular momentum (OAM) whereas that from zero quark OAM is suppressed at the threshold. From our analysis, we also show that there is no direct connection between the near threshold heavy quarkonium photoproduction and the gluonic gravitational form factors of the nucleon without additional approximation. Based on the comparison between our result and recent GlueX data of $J/\psi$ photoproduction, we make predictions for $\psi'$ and $\Upsilon$ (1S,2S) states which can be tested in future experiments.