Photoproduction of ${\eta }_c\gamma$ pairs in CGC framework

Abstract

In this paper we analyzed the exclusive photoproduction of ${\eta }_c\gamma$ pairs in the Color Glass Condensate framework. We found that the cross-section of this process is sensitive only to the forward dipole scattering amplitude, and thus could be used as a new tool for analysis of this fundamental nonperturbative object. Using the phenomenological parametrizations of this object, we estimated numerically the production cross-section and counting rates in the kinematics of the ongoing and forthcoming experiments at LHC and future Electron Ion Collider. We found that the cross-section is sufficiently large for dedicated experimental study. We also estimated the role of this process as a potential background to ${\eta }_c$ photoproduction, which is conventionally considered as a gateway for studies of odderons. We found that the contribution of ${\eta }_c\gamma$ (with undetected photon) is on par with expected contributions of odderons in the kinematics of small momentum transfer $|t|\lesssim 1$ GeV${}^2$, though decreases rapidly at larger $|t|$. Finally, we also calculated the feed-down contribution (from radiative decays of other charmonia) and found that a sizable correction comes from $J/\psi \to {\eta }_c\gamma$ decays. This contribution remains pronounced even at relatively large $|t|$ and potentially can impose constraint on detectability of odderons via ${\eta }_c$ photoproduction.

Comments: 28 pages, 12 figures. This study complements our previous analysis arXiv:2408.01822, which was done in collinear factorization framework