### Speaker

### Description

This poster will present a measurement of the charge conjugation and parity ($CP$) properties in the Higgs boson interaction with $\tau$ leptons. The Yukawa interaction is generalized with a single mixing angle parameter $\phi_{\tau}$ to describe $CP$-odd interactions between the Higgs boson and $\tau$ leptons. The study is based on a measurement of $CP$-sensitive angular observables defined by the visible decay products of $\tau$ lepton decays, performed using a data sample corresponding to 139 fb$^{-1}$ of proton–proton collisions recorded at a center-of-mass energy of $\sqrt{s}$= 13 TeV with the ATLAS detector at the Large Hadron Collider.

Without assuming Standard Model hypothesis for the $H\rightarrow\tau\tau$ signal strength,

the mixing angle $\phi_{\tau}$ is measured to be $9 \pm 16^{\circ}$, with an expected value of $0 \pm 28^{\circ}$ at the 68\% confidence level.

The pure $CP$-odd hypothesis is disfavoured at 3.4 standard deviations.

The results are compatible with the predictions for the Higgs boson in the Standard Model as well as $CP$-violating scenarios.