The observation of Higgs boson production in association with a topquark pair (t (t) over barH), based on the analysis of proton-protoncollision data at a centre-of-mass energy of 13 TeV recorded with theATLAS detector at the Large Hadron Collider, is presented. Using datacorresponding to integrated luminosities of up to 79.8 fb(-1), andconsidering Higgs boson decays into b (b) over bar, WW{*}, tau(+)tau(-),gamma gamma, and ZZ{*}, the observed significance is 5.8 standarddeviations, compared to an expectation of 4.9 standard deviations.Combined with the t (t) over barH searches using a dataset correspondingto integrated luminosities of 4.5 fb(-1) at 7 TeV and 20.3 fb(-1) at 8TeV, the observed (expected) significance is 6.3 (5.1) standarddeviations. Assuming Standard Model branching fractions, the total t (t)over barH production cross section at 13 TeV is measured to be 670 +/-90(stat.)(-100)(+110)(syst.) fb, in agreement with the Standard Modelprediction. (c) 2018 The Author(s). Published by Elsevier B.V.

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

Capua, M.;Mastroberardino, A.;Meoni, E.;