Search for Higgs boson production in association with top quark pairs in pp collisions

We present a search for the standard model Higgs boson produced in association with a top quark pair in 5~fb$^{-1}$ of 7 TeV $pp$ collision data. We look for events where the Higgs boson decays to $b\bar{b}$ and the top quark pair decays to either lepton plus jets ($t\bar{t} \rightarrow \ell\nu jjb\bar{b}$) or dileptons ($t\bar{t} \rightarrow \ell \nu \ell \nu b\bar{b}$), where $\ell$ is an electron or muon. The major background to our signal is top pair production. We use artificial neural networks to discriminate between background and signal events. We perform a simultaneous fit for signal and background fractions using the neural network output distributions. Our expected limit on Higgs boson production cross section times $H \to b\bar{b}$ branching ratio for a Higgs boson mass of 125 GeV/c$^2$ is 4.6 times the standard model expectation, while the observed limit is 3.8 times the standard model expectation.