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

Abstract

A search for the Standard Model Higgs boson produced in association with a pair of top quarks, \(t\bar{t}H\), is presented. The analysis uses 20.3 fb\(^{-1}\) of pp collision data at \(\sqrt{s}\) = 8 TeV, collected with the ATLAS detector at the Large Hadron Collider during 2012. The search is designed for the H to \(b\bar{b}\) 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 \(t\bar{t}\)+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 \(t\bar{\)+\(\b\bar{b}\) 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 \(t\bar{t}H\) signal cross section to the Standard Model expectation is found to be \(\mu = 1.5 \pm 1.1\) assuming a Higgs boson mass of 125 GeV.