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

A. M. Sirunyan et al. (CMS Collaboration)

The first observation of the $t\overline{t}H$ 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 $\sqrt{s}=13\mathrm{TeV}$ collected by the CMS detector at the LHC, corresponding to an integrated luminosity of $137{\mathrm{fb}}^{-1}$. The cross section times branching fraction of the $t\overline{t}H$ process is measured to be ${\sigma }_{t\overline{t}H}{B}_{\gamma \gamma }={1.56}_{-0.32}^{+0.34}\mathrm{fb}$, which is compatible with the standard model prediction of ${1.13}_{-0.11}^{+0.08}\mathrm{fb}$. The fractional contribution of the $CP$-odd component is measured to be $f_{CP}^{Htt}=0.00\pm 0.33$.

Phys. Rev. Lett. 125, 061801 

The published article is available at https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.061801