Measurements of t t-bar H production and the CP structure of the Yukawa interaction between the Higgs boson and top quark in the diphoton decay channel

The first observation of the t ̄tH process in a single Higgs boson decay channel with the full reconstruction of the final state (H→γγ) is presented, with a significance of 6.6 standard deviations (σ). 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 3.2σ. The measurements are based on a sample of proton-proton collisions at a center-of-mass energy √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 t ̄tH process is measured to be σt ̄tHBγγ=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 fHttCP=0.00±0.33.