Muenstermann, Daniel (2015) Search for the Standard Model Higgs boson produced in association with top quarks and decaying into bb in pp collisions at √s =8TeV with the ATLAS detector. European Physical Journal C: Particles and Fields, 75: 349. ISSN 1434-6044
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Abstract
A search for the Standard Model Higgs boson produced in association with a top-quark pair, tt ¯ H , is presented. The analysis uses 20.3 fb−1 of pp collision data at s √ =8TeV , 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. In order to improve the sensitivity of the search, events are categorised according to their jet and b-tagged jet multiplicities. A neural network is used to discriminate between signal and background events, the latter being dominated by tt ¯ +jets production. In the single-lepton channel, variables calculated using a matrix element method are included as inputs to the neural network to improve discrimination of the irreducible tt ¯ +bb ¯ background. No significant excess of events above the background expectation is found and an observed (expected) limit of 3.4 (2.2) times the Standard Model cross section is obtained at 95 % confidence level. The ratio of the measured tt ¯ H signal cross section to the Standard Model expectation is found to be μ=1.5±1.1 assuming a Higgs boson mass of 125GeV.