Simultaneous Probe of the Charm and Bottom Quark Yukawa Couplings Using tt̄H Events

A search for the standard model Higgs boson decaying to a charm quark-antiquark pair, 𝐻→𝑐⁢𝑐̄, produced in association with a top quark-antiquark pair (tt̄H) is presented. The search is performed with data from proton-proton collisions at √𝑠 =13 TeV, corresponding to an integrated luminosity of 138 fb⁻¹. Advanced machine learning techniques are employed for jet flavor identification and event classification. The Higgs boson decay to a bottom quark-antiquark pair is measured simultaneously and the observed tt̄H⁢(𝐻→𝑏⁢b̄) event rate relative to the standard model expectation is 0.91+0.26−0.22. The observed (expected) upper limit on the product of production cross section and branching fraction 𝜎⁡(tt̄H)⁢ℬ⁡(𝐻→𝑐⁢𝑐̄) is 0.11 (0.13) pb at 95% confidence level, corresponding to 7.8 (8.7) times the standard model prediction. When combined with the previous search for 𝐻 →𝑐⁢𝑐̄ via associated production with a 𝑊 or 𝑍 boson, the observed (expected) 95% confidence interval on the Higgs-charm Yukawa coupling modifier, 𝜅_𝑐, is |𝜅_𝑐| <3.5 (2.7), the most stringent constraint to date.