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

TL;DR

This paper highlights an overlooked significant source of $ ext{eta}_c$ production at the LHC, stemming from radiative decay of $J/ ext{psi}$ mesons, which can dominate over previously considered exclusive channels.

Contribution

It identifies a major additional source of $ ext{eta}_c$ production in ultra-peripheral collisions, emphasizing the importance of $J/ ext{psi}$ decay contributions.

Findings

$J/ ext{psi}$ decay significantly contributes to $ ext{eta}_c$ production.

This source can dominate over exclusive photon-induced channels.

$ ext{eta}_c$ kinematics are similar to $J/ ext{psi}$, affecting detection strategies.

Abstract

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. In $J/\psi\rightarrow\gamma\eta_c$, the photon is very soft and therefore easy to miss, and the $\eta_c$ will have very similar kinematics to the $J/\psi$.