Search for CP violation in $\mathrm{t}\bar{\mathrm{t}}\mathrm{H}$ and $\mathrm{t}\mathrm{H}$ production in multilepton channels at $\sqrt{s} = 13~\mathrm{TeV}$

We measure the CP structure of the Yukawa interaction between the Higgs boson ($\mathrm{H}$) and one or two top quarks in a data sample enriched in the $\mathrm{t}\bar{\mathrm{t}}\mathrm{H}$ and $\mathrm{t}\mathrm{H}$ associated production, using $138~\mathrm{fb}^{-1}$ of data collected in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ by the CMS experiment at the CERN LHC, and targeting events where the $\mathrm{H}$ decays via $\mathrm{H} \to \mathrm{W}\mathrm{W}$ or $\mathrm{H}\to\tau\tau$ and top quarks decay either leptonically or hadronically. We apply machine learning techniques to final states characterized by the presence of at least two leptons to enhance the separation of CP-even from CP-odd scenarios. Two-dimensional confidence regions are set on the ratios $\kappa_{t}$ and $\widetilde{\kappa_{t}}$ of the couplings of CP-even and CP-odd Lagrangian terms, respectively, to the SM expectation for the top-Higgs Yukawa coupling. Fractionary CP-odd contributions are not observed; the corresponding $f_{CP}^{Htt}$ parameter is determined to be $|f_{CP}^{Htt}| = 0.59$ with an interval of $(0.24, 0.81)$ at $68\%$ confidence level. The results are combined with previously published analyses covering the $\mathrm{H}\to\mathrm{Z}\mathrm{Z}$ and $\mathrm{H}\to\gamma\gamma$ decay modes, yielding two- and one-dimensional confidence regions on $\kappa_{t}$ and $\widetilde{\kappa_{t}}$, while $f_{CP}^{Htt}$ is determined to be $|f_{CP}^{Htt}| = 0.28$ with an interval of $|f_{CP}^{Htt}|<0.55$ at $68\%$ confidence level.