Probing the Higgs boson CP properties in vector-boson fusion production in the $H\rightarrow\tau^+\tau^-$ channel with the ATLAS detector

TL;DR

This study investigates the CP properties of the Higgs boson in vector-boson fusion production using ATLAS data, employing the Optimal Observable method to set limits on CP-violating interactions within an effective field theory framework.

Contribution

It provides the first constraints on CP-violating Higgs interactions in the VBF channel using the $H ightarrow\tau^+\tau^-$ decay mode with a large dataset at 13 TeV.

Findings

No deviations from the Standard Model observed.

Constraints placed on CP-violating parameters within effective field theory.

Limits on $ ilde{d}$ and $c_{H\tilde{W}}$ parameters at 95% CL.

Abstract

The CP properties of the Higgs boson are studied in the vector-boson fusion production mode. The analysis exploits the decay mode of the Higgs boson into two $\tau$-leptons using 140 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV collected by the ATLAS experiment at the Large Hadron Collider. Results are obtained using the Optimal Observable method. CP-violating interactions between the Higgs boson and electroweak gauge bosons are considered in the effective field theory framework, with the interaction strength described in the HISZ basis by $\tilde{d}$, and in the Warsaw basis by $c_{H\tilde{W}}$, $c_{H\tilde{B}}$, and $c_{H\tilde{W}B}$. No deviations relative to the Standard Model are observed, and limits are obtained on the strength parameters. The $\tilde{d}$ parameter is constrained to the interval [$-0.012, 0.044$] at the 95% confidence level while $c_{H\tilde{W}}$ is constrained to [$-0.24, 0.83$], when considering both linear and quadratic effects of physics beyond the Standard Model.