Abstract
The observation of Higgs boson production in association with a top quark pair (tt¯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 bb¯, 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 tt¯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 tt¯H production cross section at 13 TeV is measured to be 670 ± 90 (stat.) −100+110 (syst.) fb, in agreement with the Standard Model prediction.
Highlights
After the discovery of the Higgs boson in 2012 by the ATLAS and CMS Collaborations [1,2], many measurements of its properties were performed [3,4,5,6,7,8]
Indirect measurements of the Yukawa coupling between the Higgs boson and the top quark were made by the ATLAS and CMS Collaborations [3], assuming no contribution from unknown particles in the gluon– gluon fusion loop
The dominant uncertainties arise from the modelling of the tt+ heavy-flavour processes in the H → bbanalysis [15] and the modelling of the ttH process, which affects the acceptance of the selection in all Measured total ttH production cross sections at 13 TeV, as well as observed (Obs.) and expected (Exp.) significances relative to the background-only hypothesis
Summary
After the discovery of the Higgs boson in 2012 by the ATLAS and CMS Collaborations [1,2], many measurements of its properties were performed [3,4,5,6,7,8]. Both the Had BDT and the Lep BDT use the scaled photon pT/mγ γ observable to prevent the diphoton mass being used as a discriminating variable by the BDT This is further verified using fits of the functional forms chosen in each BDT bin in several additional control regions in data and simulation, and no evidence of a bias is found. The observed events and expected background yields in the two Had BDT bins and the Lep region, in a four-lepton invariant mass window of 115 GeV < m4 < 130 GeV, are used as in-.
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