Probing CP Violation through Vector Boson Fusion at High-Energy Muon Colliders

Abstract

We investigate CP-violating effects in electroweak interactions at future high-energy muon colliders within the Standard Model Effective Field Theory (SMEFT) framework. Focusing on four dimension-six CP-odd operators -- ${\mathcal{O}}_{\tilde{W}},{\mathcal{O}}_{H\tilde{W}},{\mathcal{O}}_{H\tilde{W}B},{\mathcal{O}}_{H\tilde{B}}$ -- we analyze vector boson fusion production of $W$ and Higgs bosons using CP-odd observables and their asymmetries. With detailed simulations including parton showering, hadronization, and detector effects, we derive exclusion sensitivities through a binned likelihood analysis. For example, at $\sqrt{s}=3$ TeV with 2 ab${}^{-1}$, the coefficient $C_{\tilde{W}}$ can be constrained at the $\mathcal{O}(0.02)$ level, improving to $\mathcal{O}(0.008)$ at 10 TeV with 2 ab${}^{-1}$, and $\mathcal{O}(0.003)$ with 10 ab${}^{-1}$. These results significantly surpass current LHC and projected ILC sensitivities, demonstrating the unique potential of high-energy muon colliders to provide direct and model-independent probes of CP violation in the electroweak sector.

7 pages, 2 figures, 11 tables