Search for the Standard Model Higgs boson produced in association with top quarks and decaying into bb in pp collisions at √s = 8 TeV with the ATLAS detector

G Aad, Tracey Berry, Jacobo Blanco, Veronique Boisvert, Timothy Brooks, Ian Connelly, Glen Cowan, Liam Duguid, Michele Faucci Giannelli, Simon George, Stephen Gibson, Jacob Kempster, Jose G Panduro Vazquez, Francesca Pastore, Graham Savage, Francesco Spano, Pedro Teixeira-Dias, Joshuha Thomas-Wilsker, The ATLAS Collaboration

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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.
Original languageEnglish
Article number349
Pages (from-to)1-50
Number of pages50
JournalEuropean Physical Journal C: Particles and Fields
Volume75
DOIs
Publication statusPublished - 29 Jul 2015

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