Search for flavor-changing neutral current interactions of the top quark mediated by a Higgs boson in proton-proton collisions at 13 TeV

A search for flavor-changing neutral current interactions of the top quark ($ t$) and the Higgs boson ($ H$) is presented. The search is based on proton-proton collision data collected in 2016–2018 at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and corresponding to an integrated luminosity of $ 138\text{}\text{}{\mathrm{fb}}^{-1}$. Events containing a pair of leptons with the same-sign electric charge and at least one jet are considered. The results are used to constrain the branching fraction ($ \mathcal{B}$) of the top quark decaying to a Higgs boson and an up ($ u$) or charm ($ c$) quark. No significant excess above the estimated background was found. The observed (expected) upper limits at a 95% confidence level are found to be 0.072% (0.059%) for $ \mathcal{B}(t\to Hu)$ and 0.043% (0.062%) for $ \mathcal{B}(t\to Hc)$. These results are combined with two other searches performed by the CMS Collaboration for flavor-changing neutral current interactions of top quarks and Higgs bosons in final states where the Higgs boson decays to either a pair of photons or a pair of bottom quarks. The resulting observed (expected) upper limits at the 95% confidence level are 0.019% (0.027%) for $ \mathcal{B}(t\to Hu)$ and 0.037% (0.035%) for $ \mathcal{B}(t\to Hc)$.