Comment on "$\eta_c$ production in photon-induced interactions at the LHC"

Understand

In "$\eta_c$ production in photon-induced interactions at the LHC," \cite{Goncalves:2018yxc} Goncalves and Moreira discuss inclusive and exclusive $\eta_c$ production at $pp$ and $pA$ collisions at LHC energies.

• The exclusive channels are via two-photon and photon-Odderon interactions.
• This comment points out that there is a large additional source of almost-exclusive $\eta_c$ in ultra-peripheral collisions: from the radiative decay of $J/\psi$ that are produced in photon-nucleon interactions.
• Although the $J/\psi\rightarrow\gamma\eta_c$ branching ratio is small, the $J/\psi$ production cross-section is large enough that it dominates over the exclusive channels considered in \cite{Goncalves:2018yxc}, and is comparable to the non-exclusive production.