Measurements of tt¯H Production and the C P Structure of the Yukawa Interaction between the Higgs Boson and Top Quark in the Diphoton Decay Channel

Abstract

The first observation of the t ¯t H process in a single Higgs boson decay channel with the full reconstruction of the final state ( H → γ γ ) 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 σ t ¯ t H B γ γ = 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 f H t t C P = 0.00 ± 0.33 .