Abstract
A search is presented for the associated production of a standard model Higgs boson with a top quark-antiquark pair ( mathrm{t}overline{mathrm{t}}mathrm{H} ), in which the Higgs boson decays into a b quark-antiquark pair, in proton-proton collisions at a centre-of-mass energy sqrt{s}=13 TeV. The data correspond to an integrated luminosity of 35.9 fb−1 recorded with the CMS detector at the CERN LHC. Candidate mathrm{t}overline{mathrm{t}}mathrm{H} events are selected that contain either one or two electrons or muons from the mathrm{t}overline{mathrm{t}} decays and are categorised according to the number of jets. Multivariate techniques are employed to further classify the events and eventually discriminate between signal and background. The results are characterised by an observed mathrm{t}overline{mathrm{t}}mathrm{H} signal strength relative to the standard model cross section, μ = σ/σSM, under the assumption of a Higgs boson mass of 125 GeV. A combined fit of multivariate discriminant distributions in all categories results in an observed (expected) upper limit on μ of 1.5 (0.9) at 95% confidence level, and a best fit value of 0.72 ± 0.24(stat) ± 0.38(syst), corresponding to an observed (expected) signal significance of 1.6 (2.2) standard deviations above the background-only hypothesis.
Highlights
√ quark-antiquark pair, in proton-proton collisions at a centre-of-mass energy s = 13 TeV
The results are characterised by an observed ttH signal strength relative to the standard model cross section, μ = σ/σSM, under the assumption of a Higgs boson mass of 125 GeV
The searches in the H → bb decay channel were performed with several analysis techniques [27, 29, 30], yielding a most stringent observed upper limit on μ of 3.4 (2.2) at the 95% confidence level (CL). √
Summary
Several BSM physics scenarios predict a significantly enhanced production rate of events with ttH final states, while not modifying the branching fractions of Higgs boson decays by a measurable amount [17,18,19,20,21,22,23,24,25,26]. In this context, a measurement of the ttH production cross section has the potential to distinguish the SM Higgs mechanism of generating fermion masses from alternative ones. The searches in the H → bb decay channel were performed with several analysis techniques [27, 29, 30], yielding a most stringent observed (expected) upper limit on μ of 3.4 (2.2) at the 95% confidence level (CL). √
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