Near Threshold Heavy Quarkonium Photoproduction at Large Momentum Transfer

TL;DR

This paper uses perturbative QCD to analyze near-threshold heavy quarkonium photoproduction at large momentum transfer, highlighting the dominant role of three-quark Fock states with quark orbital angular momentum and making testable predictions for various quarkonium states.

Contribution

It introduces a detailed QCD-based analysis of heavy quarkonium photoproduction near threshold, emphasizing the significance of quark orbital angular momentum contributions.

Findings

Three-quark Fock state with one unit of quark OAM dominates near threshold.

Zero quark OAM contribution is suppressed at the threshold.

Predictions for $Apsi'$ and $AUpsilon$ states are provided for future experimental tests.

Abstract

Perturbative QCD is applied to investigate the near threshold heavy quarkonium photoproduction 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. 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.