Study of the spin and parity of the Higgs boson in diboson decays with the ATLAS detector

TL;DR

This study analyzes the spin, parity, and tensor couplings of the Higgs boson using ATLAS data, confirming the Standard Model's predictions and excluding alternative models with high confidence.

Contribution

It provides the first comprehensive test of the Higgs boson's spin and parity properties and constrains non-Standard Model tensor couplings using multiple decay channels.

Findings

Standard Model Higgs hypothesis is confirmed with >99.9% confidence.

Alternative spin models are excluded at high confidence levels.

Tensor structure measurements are consistent with SM predictions.

Abstract

Studies of the spin, parity and tensor couplings of the Higgs boson in the $H\rightarrow ZZ^*\rightarrow 4\ell$, $H\rightarrow WW^* \rightarrow e\nu\mu\nu$ and $H\rightarrow \gamma \gamma$ decay processes at the LHC are presented. The investigations are based on $25$ fb$^{-1}$ of $pp$ collision data collected by the ATLAS experiment at $\sqrt{ s} = 7$ TeV and $\sqrt{ s }= 8$ TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers $J ^P=0^+$, is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9% confidence level. Using the $H\rightarrow ZZ^*\rightarrow 4\ell$ and $H\rightarrow WW^* \rightarrow e\nu\mu\nu$ decays, the tensor structure of the $HVV$ interaction in the spin-0 hypothesis is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplings are compatible with the SM predictions and constraints on the non-SM couplings are derived.