Abstract
The sensitivities to the anomalous quartic gauge boson coupling γγγZ are estimated via γZ 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 fb−1 and 3000 fb−1. The sensitivity we obtain at 300 fb−1 goes beyond the one expected from LHC bounds on the Z → γγγ decay by about three orders of magnitude. The γZ channel provides important discriminatory information with respect to the exclusive γγ 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.
Highlights
The γγγZ interactions in the SM and beyondThe γγγZ interaction is induced at one-loop level in the SM via loops of fermions and W bosons
The anomalous γγ → γZ process with intact protons in the final state has been implemented in the Forward Physics Monte Carlo (FPMC) generator [41]
The forward proton detectors recently installed at the LHC provide the opportunity of measuring the anomalous γγγZ coupling with unprecedented sensitivity, providing another high precision probe into the SM gauge sector
Summary
The γγγZ interaction is induced at one-loop level in the SM via loops of fermions and W bosons. The rare SM decay Z → γγγ is another process sensitive to the anomalous γγγZ interaction. In the presence of New Physics with a mass scale Λ heavier than the experimentally accessible energy E, all New Physics manifestations can be described using an effective Lagrangian valid for Λ E. In this low-energy effective field theory (EFT), the γγγZ interactions are described by two dimension-eight γγγZ operators. Because of the large number of effective operators in the SU(2) × U(1)Y Lagrangian, anomalous interactions in the broken phase can be considered as independent. As a caveat, we stress that unless the underlying New Physics model is very strongly coupled, the EFT typically breaks down before unitarity is violated
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