Searching for the neutral triple gauge couplings in the process $\mu^+\mu^-\to \gamma \nu\bar{\nu}$ at muon colliders

TL;DR

This paper assesses the potential of future high-energy muon colliders to detect neutral triple gauge couplings via the process  at energies up to 30 TeV, using SMEFT with 14 dimension-8 operators, and finds they can surpass current LHC bounds and EDM constraints.

Contribution

It extends previous analyses by including a comprehensive set of 14 dimension-8 operators and evaluates collider sensitivity with beam polarization and event strategies.

Findings

Muon colliders can set stronger bounds on nTGCs than LHC.

Annihilation dominates over VBF at TeV energies.

Constraints on pure gauge operators surpass EDM limits.

Abstract

We investigate the sensitivity of future high-energy muon colliders to neutral triple gauge couplings (nTGCs) through the process $\mu^{+}\mu^{-}\to\gamma\nu\bar{\nu}$ within the Standard Model Effective Field Theory (SMEFT) framework. Extending beyond previous studies, we consider a set of 14 dimension-8 operators, including both Higgs-related and pure gauge structures. By computing the cross sections and performing Monte Carlo simulations at multiple center-of-mass energies (3-30 TeV), we demonstrate that the annihilation process dominates over vector boson fusion (VBF) at TeV scales. We also explore the impact of beam polarization and show that the $(-+)$ polarization enhances sensitivity to several operators. After the study of the event selection strategies, we show that muon colliders can impose stronger expected constraints on nTGCs operators than current LHC bounds, with two of the pure gauge operators yielding the most stringent expected constraints. We also evaluate the contribution of CP-violating pure gauge operators to the electron electric dipole moment (EDM), finding that the expected constraints from muon colliders are stronger than those from EDM measurements.