Search for Higgs boson production in association with a top quark pair 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 and the top quark pair decays to either lepton plus jets (t → ℓνjjb) or dileptons (t → ℓνℓνb), where ℓ 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 → b branching ratio for a Higgs boson mass of 125 GeV/c2 is 4.6 times the standard model expectation, while the observed limit is 3.8 times the standard model expectation.