Probing the anomalous $\gamma \gamma \gamma Z$ coupling at the LHC with proton tagging

Abstract

The sensitivities to the anomalous quartic gauge boson coupling $\gamma \gamma \gamma Z$ are estimated via $\gamma Z$ production with intact protons in the forward region at the LHC. Proton tagging proves to be a powerful tool to suppress the background, which allows consideration of the hadronic decays of the $Z$ boson in addition to the leptonic ones. We discuss the discovery potential for an integrated luminosity of $300{\mathrm{fb}}^{-1}$ and $3000{\mathrm{fb}}^{-1}$. The sensitivity we obtain at $300{\mathrm{fb}}^{-1}$ goes beyond the one expected from LHC bounds on the $Z\to \gamma \gamma \gamma$ decay by about three orders of magnitude. The $\gamma Z$ channel provides important discriminatory information with respect to the exclusive $\gamma \gamma$ channel, as many particles beyond the Standard Model (such as a radion or Kaluza Klein gravitons) predict a signal in the latter but not the former.

Comments: 16 pages, 6 figures. v2 matches journal version