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arXiv · 1804.05293

Gluon GPDs and Exclusive Photoproduction of a Quarkonium in Forward Region

Z. L. Cui·M. C. Hu·J. P. Ma
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Abstract

Forward photoproduction of $J/\psi$ can be used to extract Generalized Parton Distributions(GPD's) of gluons. We analyze the process at twist-3 level and study relevant classifications of twist-3 gluon GPD's. At leading power or twist-2 level the produced $J/\psi$ is transversely polarized. We find that at twist-3 the produced $J/\psi$ is longitudinally polarized. Our study shows that in high energy limit the twist-3 amplitude is only suppressed by the inverse power of the heavy quark mass relatively to the twist-2 amplitude. This indicates that the power correction to the cross-section of unpolarized $J/\psi$ can have a sizeable effect. We have also derived the amplitude of the production of $h_c$ at twist-3, but the result contains end-point singularities. The production of other quarkonia has been briefly discussed.

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Z. L. Cui, M. C. Hu, J. P. Ma. 2018-04-15. Gluon GPDs and Exclusive Photoproduction of a Quarkonium in Forward Region. https://doi.org/10.1140/epjc%2Fs10052-019-7298-y

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