Gluon GPDs and exclusive photoproduction of quarkonium in forward region

• Published in: The European physical journal. C, Particles and fields Vol. 79; no. 10; pp. 1 - 10
• Main Authors: Cui, Z. L., Hu, M. C., Ma, J. P.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-10-2019; Springer; Springer Nature B.V; SpringerOpen
• Subjects: Amplitudes; Astronomy; Astrophysics and Cosmology; Elementary Particles; Gluons; Hadrons; Heavy Ions; Measurement Science and Instrumentation; Nuclear Energy; Nuclear Physics; Partons; Photoproduction; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quarks; Regular Article - Experimental Physics; Singularities; String Theory
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-019-7298-y

Forward photoproduction of
J
/
ψ
can be used to extract generalized parton distributions (GPDs) of gluons. We analyze the process at twist-3 level and study relevant classifications of twist-3 gluon GPDs. At leading power or twist-2 level the produced
J
/
ψ
is transversely polarized. We find that at twist-3 the produced
J
/
ψ
is longitudinally polarized. Our study shows that in the 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
/
ψ
can have a sizable effect.The poles in the hard factor convoluted with twist-3 gluon GPDs may concern the GPDs discontinuities, which will be briefly discussed in this work. 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.