Constraints on Anomalous Quartic Gauge Couplings via $\gamma\gamma$ and $Z\gamma$ Vector Boson Scattering at Muon Colliders

TL;DR

This study evaluates the potential of future high-energy muon colliders to detect anomalous quartic gauge couplings, demonstrating they could significantly improve current constraints and probe new physics beyond the Standard Model.

Contribution

It provides the first detailed sensitivity analysis of dimension-8 aQGCs at muon colliders using advanced simulation and multivariate analysis techniques.

Findings

Muon colliders at 3 TeV and 10 TeV can significantly tighten constraints on aQGCs.

The 10 TeV muon collider outperforms current LHC limits even with systematic uncertainties.

Advanced analysis methods improve signal detection over background noise.

Abstract

In the Standard Model, the couplings between gauge bosons are tightly constrained by the principles of gauge symmetry and renormalizability. However, the presence of anomalous couplings suggests the possibility of new physics beyond the Standard Model (BSM). In this study, we focus on the sensitivities of anomalous quartic gauge couplings (aQGCs), specially the dimension-8 operators associated with field-strength tensor structures within the effective field theory (EFT) framework, at future Muon Colliders. Our analysis targets the neutral aQGC-sensitive processes $\mu^{+}\mu^{-} \to \mu^+ \gamma \gamma \mu^-$ and $\mu^{+} \mu^{-} \to \mu^+ Z \gamma \mu^-$, simulated at center-of-mass energies of 3 TeV and 10 TeV. Signal and background events are generated using {\sc MadGraph5\_aMC@NLO}, interfaced with Pythia8 for parton showering and hadronization, and Delphes for fast detector simulation. A multivariate analysis based on Boosted Decision Trees (BDTs) is employed to enhance signal-to-background discrimination, utilizing a comprehensive set of kinematic and reconstructed observables from the final-state particles. Unitarity is preserved through the application of an energy-dependent clipping procedure within the EFT validity regime. Our findings indicate that future muon colliders offer significant sensitivity improvements over current experimental constraints on aQGCs. Furthermore, a comparison with other future collider scenarios shows that the 10 TeV Muon Collider, even with a 10\% systematic uncertainty, provides substantially stronger projected limits at 95\% confidence level than those currently reported by the ATLAS collaboration at the LHC as well as projected limits by future hadron colliders. These results underscore the enhanced potential of high-energy muon collider to probe new physics in the electroweak sector through precision measurements of aQGCs.