Search for the Standard Model Higgs boson produced in association with top quarks and decaying into a $b\bar{b}$ pair in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

TL;DR

This paper reports a search for the Standard Model Higgs boson produced with top quarks decaying into a bottom quark pair, using ATLAS data at 13 TeV, employing multivariate analysis to distinguish signal from background.

Contribution

It presents the first measurement of the $t\bar{t}H$ production cross-section in the $b\bar{b}$ decay mode at 13 TeV with detailed categorization and advanced multivariate techniques.

Findings

Measured signal strength ratio $\mu=0.84^{+0.64}_{-0.61}$

Excluded $\mu > 2.0$ at 95% CL

Expected upper limit $\mu < 1.2$

Abstract

A search for the Standard Model Higgs boson produced in association with a top-quark pair, $t\bar{t}H$, 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. The search targets the $H \to b\bar{b}$ 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 $t\bar{t}$ + jets production. For a Higgs boson mass of 125 GeV, 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 $\mu$ greater than 2.0 is excluded at 95% confidence level while the expected upper limit is $\mu < 1.2$ in the absence of a $t\bar{t}H$ signal.