Abstract
Abstract:
A search for the Standard Model Higgs boson produced in association with a top-quark pair,
tt¯H, is presented. The analysis uses 36.1 fb−1 of pp collision data at √s = 13 TeV collected
with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the H →
bb¯ decay mode. The selected events contain either one or two electrons or muons from the top-quark
decays, and are then categorized according to the number of jets and how likely these are to
contain b-hadrons. Multivariate techniques are used to discriminate between signal and background
events, the latter being dominated by tt¯ + jets production. For a Higgs boson mass of 125 GeV, the
ratio of the measured tt¯H signal cross-section to the Standard Model expectation is found to be µ
= 0.84+0.64. A value of µ greater than 2.0 is
−0.61
excluded at 95% confidence level while the expected upper limit is µ < 1.2 in the absence of
a tt¯H signal.