Kavli Affiliate: Feng Yuan
| First 5 Authors: Yuxun Guo, Xiangdong Ji, Feng Yuan, ,
| Summary:
We study the exclusive near-threshold photo-production of heavy quarkonium in
the framework of the generalized parton distribution (GPD) factorization,
taking the $J/psi$ production as an example. Due to the threshold kinematics,
the Compton-like amplitudes are related to gluon GPDs at large skewness $xi$,
distinct from the common kinematics in asymptotic high energy where the
skewness is typically small. We discuss the nature of large-$xi$ expansion of
these amplitudes in terms of the moments of gluon GPDs in the large-$xi$
limit. Based on that, we propose several ways to extract the first few moments
of the gluon GPDs from these amplitudes, with the leading ones corresponding to
the gluonic gravitational or energy-momentum tensor form factors (GFFs). We
apply these methods to analyze the recent near-threshold $J/psi$ production
measurements by the $J/psi$ 007 experiment and GlueX collaboration, and find
that the $xi$-scaling of the measured differential cross sections is
consistent with the asymptotic behavior. However, the current data are not
accurate enough yet for a complete determination of the gluonic GFFs, and
therefore we consider some prospects for better extractions in the future.
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