LHC as a photon-photon collider: Bounds on Γ X →γ γ

In the relatively recent CMS data, there is a hint on the existence of a resonance with the mass 28 GeV coupling to muons. Such a resonance should also couple to photons through the fermion loop, therefore it can be searched for in ultraperipheral collisions (UPC) of protons. We set an upper bound on the $X \\gamma \\gamma$ coupling constant from the data on $\\mu^+ \\mu^-$ pair production in UPC at the LHC. Our approach can be used for similar resonances should they appear in the future.