CMS-PAS-HIG-16-022

CMS-PAS-HIG-16-022
Search for associated production of Higgs bosons and top quarks in multilepton final states at $\sqrt{s} =$ 13 TeV
CMS Collaboration
August 2016

Abstract: We present a search for the associated production of a standard model Higgs boson and a top quark-anti quark pair ( $\mathrm{t}\overline{\mathrm{t}}\mathrm{H}$ ), using LHC pp collision data collected by the CMS experiment at a center of mass energy of $\sqrt{s} =$ 13 TeV in 2016. The dataset corresponds to an integrated luminosity of 12.9 fb $^{-1}$ . The analysis uses events with two leptons of the same charge or at least three charged leptons, produced together with b jets, targeting Higgs boson decay modes to $\mathrm{WW}^{}$ , $\mathrm{ZZ}^{}$ , and $\tau\tau$ and leptonic decays of at least one of the top quarks. The results are combined with the 2015 dataset and yield a $\mathrm{t}\overline{\mathrm{t}}\mathrm{H}$ signal strength of 2.0 $^{+0.8} _{-0.7}$ times the standard model prediction. They are used to set a 95% confidence level upper limit on the signal production cross section of 3.4 times the standard model expectation, compared to an expected upper limit of 1.3 $^{+0.6} _{-0.4}$ in the absence of a signal.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1-a: Possible Feynman diagrams for ${ {\mathrm {t}\overline {\mathrm {t}}} {\mathrm {H}} }$ production at pp colliders, where the Higgs boson decays to ${\mathrm {W}} {\mathrm {W}}^{}$ , ${\mathrm {Z}} {\mathrm {Z}} ^{}$ , and ${\tau } {\tau }$ (from a to c). Subsequent WZ, and t decays are shown representing examples of final states with four leptons, three leptons, and two same-sign leptons, respectively.
png pdf	Figure 1-b: Possible Feynman diagrams for ${ {\mathrm {t}\overline {\mathrm {t}}} {\mathrm {H}} }$ production at pp colliders, where the Higgs boson decays to ${\mathrm {W}} {\mathrm {W}}^{}$ , ${\mathrm {Z}} {\mathrm {Z}} ^{}$ , and ${\tau } {\tau }$ (from a to c). Subsequent WZ, and t decays are shown representing examples of final states with four leptons, three leptons, and two same-sign leptons, respectively.
png pdf	Figure 1-c: Possible Feynman diagrams for ${ {\mathrm {t}\overline {\mathrm {t}}} {\mathrm {H}} }$ production at pp colliders, where the Higgs boson decays to ${\mathrm {W}} {\mathrm {W}}^{}$ , ${\mathrm {Z}} {\mathrm {Z}} ^{}$ , and ${\tau } {\tau }$ (from a to c). Subsequent WZ, and t decays are shown representing examples of final states with four leptons, three leptons, and two same-sign leptons, respectively.
png pdf	Figure 2-a: Same-sign dilepton channel; a,b,c: flavor of the selected leptons, number of jets, number of jets passing the medium working point of the CSV tagger; d,e: distributions of the BDT classifier outputs. Distributions are shown before the signal extraction fit.
png pdf	Figure 2-b: Same-sign dilepton channel; a,b,c: flavor of the selected leptons, number of jets, number of jets passing the medium working point of the CSV tagger; d,e: distributions of the BDT classifier outputs. Distributions are shown before the signal extraction fit.
png pdf	Figure 2-c: Same-sign dilepton channel; a,b,c: flavor of the selected leptons, number of jets, number of jets passing the medium working point of the CSV tagger; d,e: distributions of the BDT classifier outputs. Distributions are shown before the signal extraction fit.
png pdf	Figure 2-d: Same-sign dilepton channel; a,b,c: flavor of the selected leptons, number of jets, number of jets passing the medium working point of the CSV tagger; d,e: distributions of the BDT classifier outputs. Distributions are shown before the signal extraction fit.
png pdf	Figure 2-e: Same-sign dilepton channel; a,b,c: flavor of the selected leptons, number of jets, number of jets passing the medium working point of the CSV tagger; d,e: distributions of the BDT classifier outputs. Distributions are shown before the signal extraction fit.
png pdf	Figure 3-a: Number of selected jets and distributions of the BDT classifier outputs for the three-lepton channel. Distributions are shown before the signal extraction fit.
png pdf	Figure 3-b: Number of selected jets and distributions of the BDT classifier outputs for the three-lepton channel. Distributions are shown before the signal extraction fit.
png pdf	Figure 3-c: Number of selected jets and distributions of the BDT classifier outputs for the three-lepton channel. Distributions are shown before the signal extraction fit.
png pdf	Figure 4-a: Combination of the BDT classifier outputs in the bins used for signal extraction, for the same-sign dilepton (a) and three-lepton (b) channels. Post-fit distributions and uncertainties are shown.
png pdf	Figure 4-b: Combination of the BDT classifier outputs in the bins used for signal extraction, for the same-sign dilepton (a) and three-lepton (b) channels. Post-fit distributions and uncertainties are shown.

Tables
png pdf	Table 1: Expected and observed yields after the selection in 2LSS and 3L final states. The rare SM backgrounds include ${\mathrm {W}}^\pm {\mathrm {W}}^\pm {\mathrm {q}} {\mathrm {q}}'$ , ${\mathrm {W}} {\mathrm {W}}$ produced in double-parton interactions, and triboson production. Uncertainties are purely statistical. The backgrounds from non-prompt leptons and charge mis-measurements are extracted from data.
png pdf	Table 2: Observed and expected asymptotic 95% CL upper limits on and best fit value of the signal strength parameter ( $\mu$ ).

Summary

A search for the associated production of a standard model Higgs boson and a top quark-anti quark pair has been performed using pp collision data collected by the CMS experiment in 2016 at a center of mass energy of

$\sqrt{s} =$ 13 TeV, and corresponding to an integrated luminosity of 12.9 fb

$^{-1}$ . The analysis targets Higgs boson decay modes to

$\mathrm{WW}^{*}$ ,

$\mathrm{ZZ}^{*}$ , and

$\tau\tau$ and leptonic decays of at least one of the top quarks. The 2016 dataset is combined with the smaller 2015 dataset at the same center of mass energy. We measure a signal strength of

$\sigma/\sigma_{\mathrm{SM}} =$ 2.0

$^{+0.8} _{-0.7}$ in the combined dataset, and set a 95% confidence level upper limit of

$\sigma < 3.4 \times \sigma_{\mathrm{SM}}$ on the signal cross section, compared to an expected upper limit of 1.3

$^{+0.6} _{-0.4}$ in absence of a signal.

Additional Figures
png pdf	Additional Figure 1-a: Logarithm of matrix element weights for ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \mathrm{ H } }$ , ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \mathrm{ W } }$ , and ${{\mathrm{ t } {}\mathrm{ \bar{t} } } {\mathrm{ Z } } }$ after the three-lepton category selection.
png pdf	Additional Figure 1-b: Logarithm of matrix element weights for ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \mathrm{ H } }$ , ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \mathrm{ W } }$ , and ${{\mathrm{ t } {}\mathrm{ \bar{t} } } {\mathrm{ Z } } }$ after the three-lepton category selection.
png pdf	Additional Figure 1-c: Logarithm of matrix element weights for ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \mathrm{ H } }$ , ${{\mathrm{ t } {}\mathrm{ \bar{t} } } \mathrm{ W } }$ , and ${{\mathrm{ t } {}\mathrm{ \bar{t} } } {\mathrm{ Z } } }$ after the three-lepton category selection.
png pdf	Additional Figure 2: Impact plot for the five nuisances having the largest effect on the fitted signal strength.
png pdf	Additional Figure 3-a: Normalized distributions of the BDT classifier outputs for the same-sign dilepton selection.
png pdf	Additional Figure 3-b: Normalized distributions of the BDT classifier outputs for the same-sign dilepton selection.
png pdf	Additional Figure 4-a: Post-fit yields in each category (a) and in each category-BDT bin (b) for the same-sign dilepton selection.
png pdf	Additional Figure 4-b: Post-fit yields in each category (a) and in each category-BDT bin (b) for the same-sign dilepton selection.
png pdf	Additional Figure 5-a: Post-fit yields in each category (a) and in each category-BDT bin (b) for the three-lepton selection.
png pdf	Additional Figure 5-b: Post-fit yields in each category (a) and in each category-BDT bin (b) for the three-lepton selection.
png pdf	Additional Figure 6: Negative log-likelihood as a function of the signal strength for the combined 2015+2016 result, as observed in the data and expected from simulation with a standard model signal. Dotted lines at 1.0 and 3.84 correspond to 68% and 95% confidence levels, respectively.
png pdf	Additional Figure 7-a: Best fit signal strength for the 2016 analysis alone, in the dilepton and trilepton channels (a), and further split into flavor categories (b).
png pdf	Additional Figure 7-b: Best fit signal strength for the 2016 analysis alone, in the dilepton and trilepton channels (a), and further split into flavor categories (b).
png pdf	Additional Figure 8-a: Best fit signal strength for the combined 2015+2016 analysis, in the dilepton and trilepton channels (a), and further split into flavor categories (b).
png pdf	Additional Figure 8-b: Best fit signal strength for the combined 2015+2016 analysis, in the dilepton and trilepton channels (a), and further split into flavor categories (b).
png pdf	Additional Figure 9-a: Lepton MVA (BDT) score of the trailing lepton in dileptonic ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ events for opposite sign pairs (a), i.e. enriched in prompt leptons, and for same-sign pairs (b), enriched in non-prompt leptons. The hatched area represents the uncertainty due to the limited sample sizes of simulated events. Leading leptons in the events are required to pass the ``tight'' selection, including an MVA score of greater than 0.75.
png pdf	Additional Figure 9-b: Lepton MVA (BDT) score of the trailing lepton in dileptonic ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ events for opposite sign pairs (a), i.e. enriched in prompt leptons, and for same-sign pairs (b), enriched in non-prompt leptons. The hatched area represents the uncertainty due to the limited sample sizes of simulated events. Leading leptons in the events are required to pass the ``tight'' selection, including an MVA score of greater than 0.75.

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