Observing CP-violating Higgs Signals with Heavy Majorana Neutrinos

TL;DR

This paper proposes a method to measure the CP-phase of a Higgs boson by analyzing decays of heavy Majorana neutrinos at the LHC, utilizing both opposite-sign and same-sign leptonic final states within a model with a fourth fermion generation.

Contribution

It introduces a novel approach to determine the Higgs CP-phase through heavy Majorana neutrino decays, considering a model with an extra fermion generation and enhanced Higgs production.

Findings

Potential to measure Higgs CP-phase at the LHC

Enhanced Higgs production via heavy quark loops

Low background from same-sign lepton signals

Abstract

We demonstrate the ability to measure the CP-phase of a Higgs boson state by looking at the decays of heavy, Majorana neutrinos in the process $pp \to H \to N N$ at the LHC. This is shown for signals with both opposite-sign ($l^{\pm} l^{\mp} W^{\pm} W^{\mp}$) and same-sign ($l^{\pm} l^{\pm} W^{\mp} W^{\mp}$) leptonic final states. These signals are investigated in the general framework of a sequential fourth generation of fermions with an additional right-handed neutrino. Such a scenario would naturally give rise to heavy Majorana neutrinos as well as significant enhancements to Higgs production via gluon fusion due to the contributions of the new, heavy quark states running in the fermion loops. Combined with the low background inherent to a same-sign lepton signal, this could be a useful way to investigate the CP-nature of a Higgs boson state at the LHC.