Measurements of tt 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 tt H 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 C P structure of Higgs boson couplings to fermions is measured, resulting in an exclusion of the pure C P -odd structure of the top Yukawa coupling at 3.2 σ . 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 ¯ t H process is measured to be σtt H Bγγ = 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 C P -odd component is measured to be fHttCP = 0.00 ± 0.33 .