Search for the Standard Model Higgs boson produced in association with top quarks and decaying to $\it{b\bar{b}}$ in $\it{pp}$ collisions at $\sqrt{s} =$ 8 TeV with the ATLAS detector at the LHC

A search for the Standard Model Higgs boson produced in association with a pair of top quarks, tt ¯ H , is presented. The analysis uses 20.3 fb −1 of pp collision data at s √ =8 TeV, collected with the ATLAS detector at the Large Hadron Collider during 2012. The search is designed for the H→bb ¯ decay mode and uses events containing one or two electrons or muons. The Higgs boson is assumed to have a mass of 125 GeV. In order to improve the sensitivity of the search, events are categorised according to their jet and b -tagged jet multiplicities. A multivariate technique is used to discriminate between signal and background events, which are dominated by tt ¯ +jets production. No significant excess of events above the background expectation is found and an observed (expected) 95 % confidence-level limit of 4.1 (2.6) times the Standard Model cross section is obtained. By performing a fit allowing for an arbitrary Higgs boson signal strength, the ratio of the measured signal strength to the Standard Model expectation is found to be μ=1.7±1.4