CMS-HIG-17-035

CMS-HIG-17-035 ; CERN-EP-2018-064
Observation of $\mathrm{t\bar{t}}\mathrm{H}$ production
CMS Collaboration
8 April 2018
Phys. Rev. Lett. 120 (2018) 231801
Abstract: The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of $\sqrt{s}= $ 7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb$^{-1}$, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, $\tau$ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26${^{+0.31}_{-0.26}}$.
Links: e-print arXiv:1804.02610 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	Additional Figures & Tables	References	CMS Publications

Figures
png pdf	Figure 1: Best fit value of the $ {{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}} $ signal strength modifier ${\mu _{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}}$, with its 1 and 2 standard deviation confidence intervals ($\sigma $), for (upper section) the five individual decay channels considered, (middle section) the combined result for 7+8 TeV alone and for 13 TeV alone, and (lower section) the overall combined result. The Higgs boson mass is taken to be 125.09 GeV. For the $ {\mathrm {H}} \to {\mathrm {Z}} {\mathrm {Z}}^*$ decay mode, ${\mu _{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}}$ is constrained to be positive to prevent the corresponding event yield from becoming negative. The SM expectation is shown as a dashed vertical line.
png pdf	Figure 2: The test statistic $q$, described in the text, as a function of ${\mu _{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}}$ for all decay modes at 7+8 TeV and at 13 TeV, separately, and for all decay modes at all CM energies. The expected SM result for the overall combination is also shown. The horizontal dashed lines indicate the $p$-values for the background-only hypothesis obtained from the asymptotic distribution of $q$, expressed in units of the number of standard deviations.

Tables

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Table 1:
Best fit value, with its uncertainty, of the $ {{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}} $ signal strength modifier ${\mu _{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}}$, for the five individual decay channels considered, the combined result for 7+8 TeV alone and for 13 TeV alone, and the overall combined result. The total uncertainties are decomposed into their statistical (Stat), experimental systematic (Expt), background theory systematic (Thbgd), and signal theory systematic (Thsig) components. The numbers in parentheses are those expected for $ {\mu _{{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}} = $ 1.

Summary

In summary, we have reported the observation of $ {{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}} $ production with a significance of 5.2 standard deviations above the background-only hypothesis, at a Higgs boson mass of 125.09 GeV. The measured production rate is consistent with the standard model prediction within one standard deviation. In addition to comprising the first observation of a new Higgs boson production mechanism, this measurement establishes the tree-level coupling of the Higgs boson to the top quark, and hence to an up-type quark.

Additional Figures

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Additional Figure 1:
Distribution of all events as a function of $\log_{10}$ S/B, where S and B are the expected signal (with $ \mu _{\mathrm {ttH}} = $ 1.0) and background yields respectively, evaluated for each bin in the combined analysis. The yields are determined using the values of the nuisance parameters after the fit to data. The expectation from background is given in gray, on top of which the signal expectation is given both for the standard model ($ \mu _{\mathrm {ttH}} = $ 1.0) expectation and the value measured in data ($ \mu _{\mathrm {ttH}} = $ 1.26).

Additional Tables

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Additional Table 1:
The contributions of the main uncertainty sources to the measurement of $ \mu _{\mathrm {ttH}} $. The total uncertainty is decomposed into four components: signal theory, background theory, experimental and statistical. Within each of the three systematic components a more detailed decomposition into specific sources is given. Due to correlations in the combined fit between nuisance parameters in different sources, the sum in quadrature for each source does not in general equal the total uncertainty of each component.

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