Model-independent probes of CP violation in the heavy scalar sector at muon colliders

TL;DR

This paper proposes a model-independent method to detect CP violation in the scalar sector at future muon colliders by analyzing vector-boson-fusion production and decay processes involving a heavy scalar.

Contribution

It introduces a novel approach to test CP violation without relying on specific models, using collider simulations to determine discovery sensitivities.

Findings

Simulated signal and background at 3 and 10 TeV muon colliders.

Established sensitivity regions in the parameter space for different heavy scalar masses.

Demonstrated that observing certain processes implies CP violation in the scalar sector.

Abstract

We propose a model-independent test of CP violation in the scalar sector. We consider a heavy neutral scalar $h_2$ with tree-level couplings at the $h_2 V V$ and $h_2 h_1 Z$ vertices (with $V=W^{\pm},Z$), alongside the 125~GeV SM-like Higgs boson $h_1$. At future muon colliders (MuC), we exploit vector-boson-fusion (VBF) production of $h_2$ followed by the decay $h_2 \to Z h_1$. In our framework, observing the single process $V V \to h_2 \to Z h_1$ implies both relevant couplings are nonzero, which is sufficient to establish CP violation in the scalar sector. We simulate signal and backgrounds at $\sqrt{s}=3~(10)$~TeV with integrated luminosity $L=0.9~(10)~\mathrm{ab}^{-1}$. We then present the expected discovery sensitivities across the $(c_2,c_{12})$ parameter space (with the coupling parameters $c_{2}$ and $c_{12}$ defined in the text) for multiple $m_{h_2}$ hypotheses.