Disentangling the Spin-Parity of a Resonance via the Gold-Plated Decay Mode

TL;DR

This paper presents a model-independent method using uni-angular distributions and observables to determine the spin, parity, and couplings of a new resonance decaying into four leptons via two Z bosons, validated through numerical analysis.

Contribution

It introduces a step-by-step, model-independent approach to identify the spin, parity, and couplings of a resonance in four-lepton decay channels using measurable angular distributions.

Findings

Uni-angular observables can distinguish different spin-parity states.

The method is validated through numerical simulations.

It provides a conclusive way to determine resonance properties.

Abstract

Searching for new resonances and finding out their properties is an essential part of any existing or future particle physics experiment. The nature of a new resonance is characterized by its spin, charge conjugation, parity, and its couplings with the existing particles of the Standard Model. If a new resonance is found in the four lepton final state produced via two intermediate $Z$ bosons, the resonance could be a new heavy scalar or a $Z'$ boson or even a higher spin particle. In such cases the step by step methodology as enunciated in this paper can be followed to determine the spin, parity and the coupling to two $Z$ bosons of the parent particles, in a fully model-independent way. In our approach we show how three uni-angular distributions and few experimentally measurable observables can conclusively tell us about the spin, parity as well as the couplings of the new resonance to two $Z$ bosons. We have performed a numerical analysis to validate our approach and showed how the uniangular observables can be used to disentangle the spin parity as well as coupling of the resonance.