Search for $t\bar{t}H$ production in the $H \rightarrow b\bar{b}$ channel

A search for the Standard Model Higgs boson produced in association with top-quark pair, $t\bar{t}H$, and targeting the $H \rightarrow b\bar{b}$ decay mode is presented. The analysis uses 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. Events must contain either one or two electrons or muons from the top-quark decays and are further categorized according to the multiplicities of jets and jets containing a b-hadron (b-jets). Two-stage multivariate techniques are used to discriminate between signal and the dominant background $t\bar{t}$ + jets. The ratio of the measured $t\bar{t}H$ signal cross-section to the Standard Model expectation is found to be $\mu = 0.84^{+0.64}_{-0.61}$. A value of μ greater than 2.0 is excluded at 95% confidence level. The expected upper limit is $\mu$ < 1.2 in the absence of a $t\bar{t}H$ signal.