Test of CP Invariance in vector-boson fusion production of the Higgs boson using the Optimal Observable method in the ditau decay channel with the ATLAS detector

TL;DR

This paper tests CP invariance in Higgs boson production via vector-boson fusion using the Optimal Observable method in the ditau decay channel, analyzing ATLAS data to constrain CP-violating interactions.

Contribution

It introduces a novel application of the Optimal Observable method to probe CP violation in Higgs production with the ATLAS detector, providing new constraints on CP-violating parameters.

Findings

No evidence of CP violation found; data consistent with Standard Model.

The CP-mixing parameter  is constrained to [-0.11, 0.05] at 68% CL.

Method demonstrates sensitivity to CP-violating interactions in Higgs production.

Abstract

A test of CP invariance in Higgs boson production via vector-boson fusion using the method of the Optimal Observable is presented. The analysis exploits the decay mode of the Higgs boson into a pair of $\tau$ leptons and is based on 20.3 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}$ = 8 TeV collected by the ATLAS experiment at the LHC. Contributions from CP-violating interactions between the Higgs boson and electroweak gauge bosons are described in an effective field theory framework, in which the strength of CP violation is governed by a single parameter $\tilde{d}$. The mean values and distributions of CP-odd observables agree with the expectation in the Standard Model and show no sign of CP violation. The CP-mixing parameter $\tilde{d}$ is constrained to the interval [-0.11,0.05] at 68% confidence level, consistent with the Standard Model expectation of $\tilde{d}=0$.