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

## TL;DR

This paper investigates the potential to detect anomalous $gamma Z$ couplings at the LHC using proton tagging, showing significant sensitivity improvements and the ability to distinguish new physics signals from other channels.

## Contribution

It introduces a novel method using proton tagging to enhance sensitivity to $gamma Z$ couplings, including hadronic $Z$ decays, at the LHC.

## Key findings

- Sensitivity at 300 fb$^{-1}$ exceeds previous bounds by three orders of magnitude.
- Proton tagging effectively suppresses background, enabling hadronic decay analysis.
- The $gamma Z$ channel offers unique insights compared to the $gamma gamma$ channel.

## 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 $Z\rightarrow \gamma\gamma\gamma$ 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.