Decays of a neutral particle with zero spin and arbitrary CP parity into two off-mass-shell Z bosons

TL;DR

This paper investigates CP violation effects in the decay of a scalar particle, like the Higgs boson, into two off-mass-shell Z bosons, analyzing how angular and mass distributions can reveal the particle's CP properties.

Contribution

It provides a general amplitude framework for Higgs decay into Z bosons with indefinite CP parity and assesses the narrow-Z-width approximation's validity.

Findings

Derived observables sensitive to CP violation.

Analyzed decay distributions within the Standard Model and beyond.

Identified experimental signatures for CP properties at the LHC.

Abstract

Effects are investigated of CP symmetry violation in the decay of a scalar particle X (the Higgs boson) into two off-mass-shell Z bosons both decaying into a fermion-antifermion pair, $X \to Z_1^* \, Z_2^* \to f_1 \bar{f_1} \, f_2 \bar{f_2}$. The most general form of the amplitude of the transition $X \to Z_1^* Z_2^*$, wherein the boson X may not have definite CP parity, is considered. Limits of applicability of the narrow-Z-width approximation used when obtaining differential widths of the decay under consideration are determined. Various observables connected with the structure of the amplitude of the decay $X \to Z_1^* Z_2^*$ are studied. These observables are analyzed in the Standard Model, as well as in models conceding indefinite CP parity of the Higgs boson. An experimental measurement at the LHC of angular and invariant mass distributions of the decay $X \to Z_1^* Z_2^* \to f_1 \bar{f_1} f_2 \bar{f_2}$ can give information about the CP properties of the Higgs boson and its interaction with the Z boson.