UC Berkeley

In "ηc production in photon-induced interactions at the LHC," [Phys. Rev. D 97, 094009 (2018)PRVDAQ2470-001010.1103/PhysRevD.97.094009] Goncalves and Moreira discuss inclusive and exclusive ηc 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 ηc in ultraperipheral collisions: from the radiative decay of J/ψ that are produced in photon-nucleon interactions. Although the J/ψ→γηc branching ratio is small, the J/ψ production cross-section is large enough that it dominates over the exclusive channels considered in [1], and is comparable to the nonexclusive production. In J/ψ→γηc, the photon is very soft and therefore easy to miss, and the ηc will have very similar kinematics to the J/ψ.