Disentangling CP phases in nearly degenerate resonances: neutralino production via Higgs at a muon collider

TL;DR

This paper investigates how CP-violating phases in the Higgs sector of the MSSM can be disentangled through neutralino production at a muon collider, focusing on CP asymmetries near nearly degenerate Higgs resonances.

Contribution

It introduces a method to analyze CP phases via neutralino production at muon colliders, emphasizing the role of nearly degenerate Higgs bosons and radiative effects.

Findings

CP asymmetries can be significantly enhanced near degenerate Higgs resonances.

Radiatively induced CP violation leads to sizable, measurable CP asymmetries.

The method is potentially applicable to other scalar resonance processes at colliders.

Abstract

In the CP-violating Minimal Supersymmetric Standard Model, we study the pair production of neutralinos at center-of-mass energies around the heavy neutral Higgs boson resonances. For longitudinally polarized muon beams, we analyze CP asymmetries which are sensitive to the interference of the two heavy neutral Higgs bosons. Due to radiatively induced scalar-pseudoscalar transitions, the CP asymmetries can be strongly enhanced when the resonances are nearly degenerate, as in the Higgs decoupling limit. The Higgs couplings to the neutralino sector can then be analyzed in the presence of CP violating phases. We present a detailed numerical analysis of the cross sections, neutralino branching ratios, and the CP observables. We find that radiatively induced CP violation in the Higgs sector leads to sizable CP-asymmetries, which are accessible in future measurements at a muon collider. However, we expect that our proposed method should be applicable to other processes with nearly degenerate scalar resonances, even at hadron colliders.