Anomalous quartic WWgamma gamma, ZZgamma gamma, and trilinear WWgamma couplings in two-photon processes at high luminosity at the LHC

TL;DR

The paper analyzes W/Z pair production via two-photon exchange at the LHC as a clean test of electroweak interactions and a probe of new physics in gauge couplings. It develops an effective-Lagrangian framework for anomalous quartic WWγγ/ZZγγ and triple WWγ interactions, implements unitarity-preserving form factors, and simulates signal and backgrounds with the Forward Physics Monte Carlo. Using forward proton detectors (AFP) and fast detector simulations, it shows the SM γγ→WW cross section of about 95.6 fb and demonstrates that 30–200 fb^-1 of data could dramatically improve quartic-coupling sensitivities (by orders of magnitude) while providing complementary constraints on triple gauge couplings. The work highlights the importance of forward-tagged exclusive events for precision electroweak tests and identifies semi-leptonic channels and background modeling as key areas for future refinement.

Abstract

We study the W/Z pair production via two-photon exchange at the LHC and give the sensitivities on trilinear and quartic gauge anomalous couplings between photons and W/Z bosons for an integrated luminosity of 30 and 200 fb^{-1}. For simplicity and to obtain lower backgrounds, only the leptonic decays of the electroweak bosons are considered.

Figures (17)

• Figure 1: Sketch diagram showing the two-photon production of a central system. Unaltered protons leave the interaction at very small angles $\lesssim100\,\mu$rad and the central system is produced alone in the central detector without any proton remnants.
• Figure 2: Relative effective $\gamma\gamma$ luminosity in $pp$ collisions at $14\,\hbox{TeV}$ as a function of the two-photon invariant mass. The maximal virtualities of the emitted photons are set to $Q^2_{max}=2\,\,\hbox{GeV}^2$. The dashed curve shows the photon spectrum within the ATLAS or CMS forward detector acceptance (discussed in section \ref{['sec:selection']}).
• Figure 3: Feynman diagrams of SM processes that contribute to the $\gamma\gamma\rightarrow WW$ scattering amplitude in the lowest order perturbation series with a coupling $e^2$. The trilinear couplings of strength $e$ are involved in diagrams a) and b) and the direct quartic coupling of strength $e^2$ in diagram c).
• Figure 4: Enhancement of the $pp\rightarrow pWWp$ and $pp\rightarrow pZZp$ cross section at $\sqrt{s}=14\,\hbox{TeV}$ with quartic-boson anomalous couplings $a_0^W$, $a_C^W$, and $a_0^Z$, $a_C^Z$ from the SM values 95.6 fb and 0, respectively. The survival probability factor is not included.
• Figure 5: Missing mass distribution showing the effect of the form factor (\ref{['eq:anom:formfactor']}) on the cross section. The signal due to the anomalous coupling appears for masses $W>800\,\hbox{GeV}$. Both leptons are in the detector acceptance and above $\hbox{$p_T$}>10\,\hbox{GeV}$.