A search for Higgs boson production in association with a pair of top quarks (tˉtH) is presented, where the Higgs boson decays to bˉb, and both top quarks decay hadronically.
The data used correspond to an integrated luminosity of 20.3 fb−1 of pp collisions at √s=8\TeV collected with the ATLAS detector at the Large Hadron Collider.
The search selects events with at least six energetic jets and uses a boosted decision tree algorithm to discriminate between signal and Standard Model background.
For a Higgs boson mass of 125 \GeV, an upper limit of 6.4 (5.4) times the Standard Model cross section is observed (expected) at 95\% confidence level.
The best fit value for the signal strength is μ=σmeasσSM=1.6±2.6 for mH=125 \GeV.
Combining all tˉtH searches carried out by ATLAS at √s=7 and 8 \TeV, an observed (expected) upper limit of 3.1 (1.4) times the Standard Model expectation is obtained at 95\% confidence level, with a signal strength μ=1.7±0.8.