Test of $CP$ Invariance in Higgs Boson Vector-Boson-Fusion Production Using the $H\to\gamma\gamma$ Channel with the ATLAS Detector

TL;DR

This paper tests $CP$ invariance in Higgs boson production via vector-boson fusion using the $H o\gamma\gamma$ channel with ATLAS data, finding no evidence of $CP$ violation and setting the most stringent constraints to date.

Contribution

It introduces a novel analysis using the Optimal Observable method to constrain $CP$-odd couplings in Higgs interactions with gauge bosons, providing the first 95% CL constraint on $ ilde{d}$.

Findings

No sign of $CP$ violation observed in data.

Most stringent constraints on $CP$-odd Higgs couplings to date.

First 95% CL constraint on $ ilde{d}$ parameter.

Abstract

A test of $CP$ invariance in Higgs boson production via vector-boson fusion has been performed in the $H\rightarrow\gamma\gamma$ channel using 139 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13\,\mathrm{TeV}$ collected by the ATLAS detector at the LHC. The Optimal Observable method is used to probe the $CP$ structure of interactions between the Higgs boson and electroweak gauge bosons, as described by an effective field theory. No sign of $CP$ violation is observed in data. Constraints are set on the parameters describing the strength of the $CP$-odd component in the coupling between the Higgs boson and the electroweak gauge bosons in two effective field theory bases: $\tilde{d}$ in the HISZ basis and $c_{H\tilde{W}}$ in the Warsaw basis. The results presented are the most stringent constraints on $CP$ violation in the coupling between Higgs and weak bosons. The 95% CL constraint on $\tilde{d}$ is derived for the first time and the 95% CL constraint on $c_{H\tilde{W}}$ has been improved by a factor of 5 compared to the previous measurement.