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CMS-PAS-B2G-17-011
Search for vector-like T or B quark pairs in leptonic final states in 36 fb$^{-1}$ of proton-proton collisions at $\sqrt{s}= $ 13 TeV
Abstract: A search is presented for pair production of heavy vector-like T or B quarks in proton-proton collisions at $\sqrt{s} = $ 13 TeV. The search uses a data sample corresponding to an integrated luminosity of 35.9 fb$^{-1}$, collected with the CMS detector at the CERN LHC in 2016. Pair production of T quarks would result in a wide range of final states, since vector-like T quarks of charge 2e/3 are predicted to decay to bW, tZ, and tH. Likewise, vector-like B quarks are predicted to decay to tW, bZ, and bH. This search is performed in three channels corresponding to final states with a single lepton, two leptons with the same electric charge sign, and at least three leptons. This search excludes T quark masses below 1140-1300 GeV and B quark masses below 910-1240 GeV for various branching fraction combinations, extending the reach of previous CMS searches by 200-600 GeV. These are the strongest exclusion limits to date for T quarks with $\mathcal{B}(\mathrm{bW}) < $ 0.6 and B quarks with $\mathcal{B}(\mathrm{tW}) < $ 0.6.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Example leading order Feynman diagrams showing pair production and decays of ${{\mathrm {T}} {\overline {\mathrm {T}}}}$ (left) and ${{\mathrm {B}} {\overline {\mathrm {B}}}}$ (right).

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Figure 1-a:
Example leading order Feynman diagrams showing pair production and decays of ${{\mathrm {T}} {\overline {\mathrm {T}}}}$ (left) and ${{\mathrm {B}} {\overline {\mathrm {B}}}}$ (right).

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Figure 1-b:
Example leading order Feynman diagrams showing pair production and decays of ${{\mathrm {T}} {\overline {\mathrm {T}}}}$ (left) and ${{\mathrm {B}} {\overline {\mathrm {B}}}}$ (right).

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Figure 2:
Distributions of (left) AK8 jet pruned mass in jets with $\tau _2/\tau _1 < $ 0.6, and (right) the n-subjettiness $\tau _2/\tau _1$ ratio in AK8 jets with pruned mass between 65-105 GeV. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 2-a:
Distributions of (left) AK8 jet pruned mass in jets with $\tau _2/\tau _1 < $ 0.6, and (right) the n-subjettiness $\tau _2/\tau _1$ ratio in AK8 jets with pruned mass between 65-105 GeV. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 2-b:
Distributions of (left) AK8 jet pruned mass in jets with $\tau _2/\tau _1 < $ 0.6, and (right) the n-subjettiness $\tau _2/\tau _1$ ratio in AK8 jets with pruned mass between 65-105 GeV. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 3:
Distributions of (left) AK8 jet pruned mass in jets with two b-tagged subjets, and (right) number of b-tagged subjets in jets with pruned mass within 60-160 GeV. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 3-a:
Distributions of (left) AK8 jet pruned mass in jets with two b-tagged subjets, and (right) number of b-tagged subjets in jets with pruned mass within 60-160 GeV. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 3-b:
Distributions of (left) AK8 jet pruned mass in jets with two b-tagged subjets, and (right) number of b-tagged subjets in jets with pruned mass within 60-160 GeV. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 4:
The $H^{\mathrm {lep}}_{\mathrm {T}}$ distributions in events with at least two jets after SS dilepton selection and Z-boson/quarkonia vetoes for each flavor category and the combination of all categories. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 4-a:
The $H^{\mathrm {lep}}_{\mathrm {T}}$ distributions in events with at least two jets after SS dilepton selection and Z-boson/quarkonia vetoes for each flavor category and the combination of all categories. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 4-b:
The $H^{\mathrm {lep}}_{\mathrm {T}}$ distributions in events with at least two jets after SS dilepton selection and Z-boson/quarkonia vetoes for each flavor category and the combination of all categories. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 4-c:
The $H^{\mathrm {lep}}_{\mathrm {T}}$ distributions in events with at least two jets after SS dilepton selection and Z-boson/quarkonia vetoes for each flavor category and the combination of all categories. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 4-d:
The $H^{\mathrm {lep}}_{\mathrm {T}}$ distributions in events with at least two jets after SS dilepton selection and Z-boson/quarkonia vetoes for each flavor category and the combination of all categories. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 5:
Distribution of $\chi ^2$ values from a scan of electron and muon misidentification rate values. The intersection of the horizontal and vertical lines, marked by an x, indicate the minimum value.

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Figure 6:
Distributions of lepton $ {p_{\mathrm {T}}} $ (left) and $ {S_\mathrm {T}} $ (right) in the control region of the trilepton channel. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 6-a:
Distributions of lepton $ {p_{\mathrm {T}}} $ (left) and $ {S_\mathrm {T}} $ (right) in the control region of the trilepton channel. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 6-b:
Distributions of lepton $ {p_{\mathrm {T}}} $ (left) and $ {S_\mathrm {T}} $ (right) in the control region of the trilepton channel. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 7:
Distributions of single-lepton channel discriminants in the W0 (left) or W1 (right) categories with 1, 2, or $\geq 3$ (top to bottom) b-tagged jets. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 7-a:
Distributions of single-lepton channel discriminants in the W0 (left) or W1 (right) categories with 1, 2, or $\geq 3$ (top to bottom) b-tagged jets. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 7-b:
Distributions of single-lepton channel discriminants in the W0 (left) or W1 (right) categories with 1, 2, or $\geq 3$ (top to bottom) b-tagged jets. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 7-c:
Distributions of single-lepton channel discriminants in the W0 (left) or W1 (right) categories with 1, 2, or $\geq 3$ (top to bottom) b-tagged jets. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 7-d:
Distributions of single-lepton channel discriminants in the W0 (left) or W1 (right) categories with 1, 2, or $\geq 3$ (top to bottom) b-tagged jets. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 7-e:
Distributions of single-lepton channel discriminants in the W0 (left) or W1 (right) categories with 1, 2, or $\geq 3$ (top to bottom) b-tagged jets. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 7-f:
Distributions of single-lepton channel discriminants in the W0 (left) or W1 (right) categories with 1, 2, or $\geq 3$ (top to bottom) b-tagged jets. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 8:
Distributions of single-lepton channel discriminants in the H1b (left) or H2b (right) categories. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 8-a:
Distributions of single-lepton channel discriminants in the H1b (left) or H2b (right) categories. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 8-b:
Distributions of single-lepton channel discriminants in the H1b (left) or H2b (right) categories. Distributions are normalized for varying bin width. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 9:
Predicted background distributions of ${S_\mathrm {T}}$ in the trilepton final state after final selection requirements are applied. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 9-a:
Predicted background distributions of ${S_\mathrm {T}}$ in the trilepton final state after final selection requirements are applied. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 9-b:
Predicted background distributions of ${S_\mathrm {T}}$ in the trilepton final state after final selection requirements are applied. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 9-c:
Predicted background distributions of ${S_\mathrm {T}}$ in the trilepton final state after final selection requirements are applied. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 9-d:
Predicted background distributions of ${S_\mathrm {T}}$ in the trilepton final state after final selection requirements are applied. Uncertainties, indicated by the hatched area, include both statistical and systematic components. The lower panel shows the difference between data and background divided by the total uncertainty.

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Figure 10:
The 95% CL expected upper limits (Bayesian) on the cross section of ${{\mathrm {T}} {\overline {\mathrm {T}}}}$ production after combining all channels for the singlet (left) and doublet (right) branching fraction scenarios.

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Figure 10-a:
The 95% CL expected upper limits (Bayesian) on the cross section of ${{\mathrm {T}} {\overline {\mathrm {T}}}}$ production after combining all channels for the singlet (left) and doublet (right) branching fraction scenarios.

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Figure 10-b:
The 95% CL expected upper limits (Bayesian) on the cross section of ${{\mathrm {T}} {\overline {\mathrm {T}}}}$ production after combining all channels for the singlet (left) and doublet (right) branching fraction scenarios.

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Figure 11:
The 95% CL expected upper limits (Bayesian) on the cross section of ${{\mathrm {B}} {\overline {\mathrm {B}}}}$ production after combining all channels for the singlet (left) and doublet (right) branching fraction scenarios.

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Figure 11-a:
The 95% CL expected upper limits (Bayesian) on the cross section of ${{\mathrm {B}} {\overline {\mathrm {B}}}}$ production after combining all channels for the singlet (left) and doublet (right) branching fraction scenarios.

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Figure 11-b:
The 95% CL expected upper limits (Bayesian) on the cross section of ${{\mathrm {B}} {\overline {\mathrm {B}}}}$ production after combining all channels for the singlet (left) and doublet (right) branching fraction scenarios.

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Figure 12:
The 95% CL expected (left) and observed (right) lower limits (Bayesian) on the T quark mass after combining all channels for various branching fraction combinations.

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Figure 12-a:
The 95% CL expected (left) and observed (right) lower limits (Bayesian) on the T quark mass after combining all channels for various branching fraction combinations.

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Figure 12-b:
The 95% CL expected (left) and observed (right) lower limits (Bayesian) on the T quark mass after combining all channels for various branching fraction combinations.

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Figure 13:
The 95% CL expected (left) and observed (right) lower limits (Bayesian) on the B quark mass after combining all channels for various branching fraction combinations.

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Figure 13-a:
The 95% CL expected (left) and observed (right) lower limits (Bayesian) on the B quark mass after combining all channels for various branching fraction combinations.

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Figure 13-b:
The 95% CL expected (left) and observed (right) lower limits (Bayesian) on the B quark mass after combining all channels for various branching fraction combinations.
Tables

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Table 1:
Predicted cross sections of ${{\mathrm {T}} {\overline {\mathrm {T}}}}$ or ${{\mathrm {B}} {\overline {\mathrm {B}}}}$ production at various masses. Uncertainties include contributions from factorization and renormalization scale variations by a factor of two, and from the PDFs.

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Table 2:
Predicted and observed event yields in the aggregated control region categories of the single-lepton channel. Uncertainties include both statistical and systematic components.

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Table 3:
Summary of systematic uncertainties with values for normalization uncertainties and dependencies for shape uncertainties. The symbol $\sigma $ denotes one standard deviation of the uncertainty and "env'' denotes an envelope of values. Prompt opposite-sign dilepton events are denoted "OS'', nonprompt lepton background is denoted "NP'', and "MC'' indicates backgrounds modeled from simulation. For signals, theoretical uncertainties are labeled as "Shape'' for shape-based searches, and "Accept.'' for counting experiments.

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Table 4:
Signal efficiencies in the single, same-sign dilepton, and trilepton channels, split into the six possible final states of both ${{\mathrm {T}} {\overline {\mathrm {T}}}}$ and ${{\mathrm {B}} {\overline {\mathrm {B}}}}$ production, for three mass points. Efficiencies are calculated with respect to the expected number of events in the corresponding decay mode before any selection. Efficiency for $ {\mathrm {b}} {\mathrm {W}} {\mathrm {b}} {\mathrm {W}}$ events in the same-sign dilepton and trilepton channels is negligible, as is efficiency for $ {\mathrm {b}} {\mathrm {Z}} {\mathrm {b}} {\mathrm {Z}} $ events in the same-sign dilepton channel.

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Table 5:
Number of predicted and observed events for signal region categories of the single-lepton channel. Uncertainties include both statistical and systematic components.

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Table 6:
Expected number of background and signal events for lepton flavor categories in the same-sign dilepton channel. Uncertainties include both statistical and systematic components.

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Table 7:
Expected number of background and signal events for lepton flavor categories in the trilepton channel. Uncertainties include both statistical and systematic components.
Summary
A search has been presented for pair-produced vector-like T and B quarks in a data sample of proton-proton collisions recorded during 2016 by the CMS experiment, and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The search is performed in channels with one lepton, two same-sign leptons, or at least three leptons in the final state and makes use of techniques to identify Lorentz-boosted hadronically decaying W and Higgs bosons. Combining these channels we exclude T (B) quarks at 95% confidence level with masses below 1200 (1170) GeV in the singlet branching fraction scenario and 1280 (940) GeV in the doublet branching fraction scenario. For other branching fraction combinations this search excludes T quark masses in the range of 1140-1300 GeV and B quark masses in the range of 910-1240 GeV. This represents improvements in sensitivity compared to previous CMS results of 200-600 GeV for most T and B quark branching combinations. These results are the strongest exclusion limits to date for T quarks with $\mathcal{B}(\mathrm{b}\mathrm{W}) < $ 0.6 and B quarks with $\mathcal{B}(\mathrm{t}\mathrm{W}) < $ 0.6.
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