The first observation of the ${\mathrm{t\bar{t}}\mathrm{H}}$ process in a single Higgs boson decay channel with the full reconstruction of the final state (${\mathrm{H} \to \gamma\gamma}$) is presented, with a significance of 6.6 standard deviations ($\sigma$). The CP structure of Higgs boson couplings to fermions is measured, resulting in an exclusion of the pure CP-odd structure of the top Yukawa coupling at 3.2$\sigma$. The measurements are based on a sample of proton-proton collisions at a center-of-mass energy $\sqrt{s}=$ 13 TeV collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb$^{-1}$. The cross section times branching fraction of the ${\mathrm{t\bar{t}}\mathrm{H}}$ process is measured to be ${\sigma_{{\mathrm{t\bar{t}}\mathrm{H}} } \mathcal{B}_{\gamma\gamma}}=$ 1.56$^{+0.34}_{-0.32}$ fb, which is compatible with the standard model prediction of 1.13$^{+0.08}_{-0.11}$ fb. The fractional contribution of the CP-odd component is measured to be ${f_{\mathrm{CP}}^{{\mathrm{H}\mathrm{t}\mathrm{t}} }} =$ 0.00 $\pm$ 0.33.

Log in to your administrator account to edit.