Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector

TL;DR

This paper reports the first observation of Higgs boson production with a top quark pair at the LHC, confirming the Standard Model prediction with a significance of over 5 standard deviations.

Contribution

It provides the first observation of the $t\bar{t}H$ process at 13 TeV, measuring its cross section and significance with multiple decay channels and datasets.

Findings

Observed significance of 5.8 sigma for $t\bar{t}H$ production.

Measured cross section of 670 ± 90 (stat.) +110/-100 (syst.) fb.

Confirmation of Standard Model predictions for Higgs-top coupling.

Abstract

The observation of Higgs boson production in association with a top quark pair ($t\bar{t}H$), based on the analysis of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider, is presented. Using data corresponding to integrated luminosities of up to 79.8 fb$^{-1}$, and considering Higgs boson decays into $b\bar{b}$, $WW^*$, $\tau\tau$, $\gamma\gamma$, and $ZZ^*$, the observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the $t\bar{t}H$ searches using a dataset corresponding to integrated luminosities of 4.5 fb$^{-1}$ at 7 TeV and 20.3 fb$^{-1}$ at 8 TeV, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total $t\bar{t}H$ production cross section at 13 TeV is measured to be 670 $\pm$ 90 (stat.) $^{+110}_{-100}$ (syst.) fb, in agreement with the Standard Model prediction.