Search for H to bbar in association with a single top quark as a test of Higgs boson couplings at 13 TeV

A direct search for the production of a Higgs boson in association with a single top quark is performed. The analysis considers single top quark production either via the $t$ channel or via the associated production with a W boson and uses Higgs boson decays to a bottom quark-antiquark pair and semileptonic top quark decays. Data recorded by the CMS detector in 2015 in pp collisions at a center-of-mass energy of $13\,\mathrm{TeV}$, amounting to an integrated luminosity of about $2.3\,\mathrm{fb}^{-1}$, are analyzed. Upper limits in the two-dimensional plane spanned by the scaling factors for the coupling strength of the Higgs boson to top quarks and to weak gauge bosons with respect to the standard model predictions, $\kappa_\text{t}$ and $\kappa_\text{V}$, are determined. The observed (expected) limit on the cross section for the production of a Higgs boson in association with a single top quark in the scenario with a negative Yukawa coupling of the top quark ($\kappa_\text{t} = -1.0$ and $\kappa_\text{V} = +1.0$) is 6.0 (6.4) times the predicted value. %Additionally, upper limits on a $\mathcal{CP}$-violating top-Yukawa coupling are estimated.