Search for ttH production in the H-to-bb decay channel with leptonic tt decays in proton-proton collisions at sqrt(s) = 13 TeV with the CMS detector

A search for the associated production of a standard model Higgs boson with a top quark-antiquark pair ($\mathrm{t\bar{t}H}$) in proton-proton collisions at a center-of-mass energy $\sqrt{s}=13~\mathrm{TeV}$ is presented. The data correspond to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$ recorded with the CMS detector at the CERN LHC in 2016. Candidate $\mathrm{t\bar{t}H}$ events are selected that contain either one or two electrons or muons from the $\mathrm{t\bar{t}}$ decays, and are categorized according to the number of jets. Multivariate techniques are employed to categorize further the events and eventually discriminate between signal and background events. The results are characterized by an observed $\mathrm{t\bar{t}H}$ signal strength relative to the standard model cross section, $\mu = \sigma/\sigma_{\mathrm{SM}}$, under the assumption of $m_{\mathrm{H}} = 125~\mathrm{GeV}$. A combined fit of multivariate discriminant distributions in all categories results in an observed (expected) upper limit of $\mu < 1.5~(0.9)$ at the $95\%$ confidence level, and a best fit value of $\mu = 0.72\pm0.45$, corresponding to an observed (expected) significance of 1.6 (2.2) standard deviations.