Measurements of $\mathrm{t\bar{t}}$H production and the CP structure of the Yukawa interaction between the Higgs boson and the top quark in the diphoton decay channel

Understand

The first observation of the $\mathrm{t\bar{t}}$H process in a single Higgs boson decay channel with the full reconstruction of the final state (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 $\mathrm{t\bar{t}}$H process is measured to be $\sigma_{\mathrm{t\bar{t}H}}\mathcal{B}_{\gamma\gamma} =$ 1.56 $^{+0.34}_{-0.32}$ fb, which is compatible with the standard model prediction of 1.13 $^{+0.08}_{-0.11}$ fb.