Analysis of the CP structure of the Yukawa coupling between the Higgs boson and tau leptons in proton-proton collisions at $ \sqrt{s}=13.6 $ TeV

A bstract: This paper presents a measurement of the charge-parity ( CP ) structure of the Yukawa coupling between the Higgs boson (H) and tau leptons, using proton-proton collision data at $$ \sqrt{s}=13.6 $$ s = 13.6 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 62.4 fb ^{− 1} . Angular correlations between the decay products of tau leptons produced in H → ττ decays are exploited to constrain the effective CP mixing angle α ^{H ττ} , which parameterizes the admixture of scalar and pseudoscalar couplings. The mixing angle is measured to be $$ {\alpha}^{\mathrm{H}\tau \tau}={\left({36}_{-30}^{+33}\right)}^{{}^{\circ}} $$ α H ττ = 36 − 30 + 33 ° , compared with an expected value of (0 ± 19) ^° under the standard model hypothesis. When combined with the previous CMS measurement using data collected at $$ \sqrt{s}=13 $$ s = 13 TeV, corresponding to an integrated luminosity of 138 fb ^{− 1} , the mixing angle is determined to be (7 ± 16) ^° , with an expected value of (0 ± 14) ^° . This result represents the most precise measurement by CMS of the CP nature of the Higgs boson coupling to tau leptons, with an expected precision that is the best achieved by any experiment to date.