Aaboud, M.Aad, G.Abbott, B.Abdinov, O.Abeloos, B.Abhayasinghe, D.K.Abidi, S.H.AbouZeid, O.S.Abraham, N.L.Abramowicz, H.Abreu, H.Abulaiti, Y.Acharya, B.S.Adachi, S.Adamczyk, L.Adelman, J.Adersberger, M.Adiguzel, A.Adye, T.Affolder, A.A.et al.2020-05-042020-05-042018Physics Letters B, 2018; 784:173-1910370-26931873-2445http://hdl.handle.net/2440/124542The observation of Higgs boson production in association with a top quark pair (t ̄tH), 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 ̄b, WW∗, τ+τ−, γγ, and ZZ∗, the observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the t ̄tHsearches using a dataset corresponding to integrated luminosities of 4.5 fb−1at 7TeVand 20.3 fb−1at 8TeV, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total t ̄tHproduction cross section at 13 TeV is measured to be 670±90 (stat.)+110−100(syst.) fb, in agreement with the Standard Model prediction.en©2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.Journal article003009569010.1016/j.physletb.2018.07.0350004457816000292-s2.0-85051211826424482