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| CMS-PAS-B2G-20-011 | ||
| Search for pair production of vector-like quarks in leptonic final states at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| May 2022 | ||
| Abstract: A search is presented for vector-like T and B quark-antiquark pairs produced in proton-proton collisions at a center-of-mass energy of 13 TeV. Data were collected by the CMS Experiment in 2016, 2017, and 2018, with an integrated luminosity of 137 fb$^{-1}$. Events with leptonic signatures are selected: one electron or muon, missing transverse energy, and at least three large-radius jets in the single-lepton channel; two electrons or muons with matching electric charge in the same-sign dilepton channel; and three or more electrons or muons in the multilepton channel. The single-lepton channel utilizes a multilayer neural network and jet identification techniques to discriminate signal events, while the same-sign dilepton and multilepton channels rely on the high-energy signature of the signal to distinguish it from rare standard model backgrounds. The production of vector-like quark pairs is excluded for T quark masses up to 1.54 TeV and B quark masses up to 1.56 TeV depending on the branching fractions assumed, with maximal sensitivity to decay modes that include multiple top quarks. These are the strongest limits to date for $\mathrm{T\overline{T}}$ production with decays to tH and bW and $\mathrm{B\overline{B}}$ production with decays to tW. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Leading order Feynman diagrams showing pair production of $\mathrm{T\overline{T}}$ (left) or $\mathrm{B\overline{B}}$ (right) with representative decays to third generation quarks and SM bosons. |
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Figure 1-a:
Leading order Feynman diagrams showing pair production of $\mathrm{T\overline{T}}$ (left) or $\mathrm{B\overline{B}}$ (right) with representative decays to third generation quarks and SM bosons. |
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Figure 1-b:
Leading order Feynman diagrams showing pair production of $\mathrm{T\overline{T}}$ (left) or $\mathrm{B\overline{B}}$ (right) with representative decays to third generation quarks and SM bosons. |
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Figure 2:
Distributions of DeepAK8 jet tags in the DeepAK8 CR (left), and ${H_{\mathrm {T}}}$ in the W+jets (center) and ${\mathrm{t} {}\mathrm{\bar{t}}}$ (right) CRs of the $\mathrm{T\overline{T}}$ search. The observed data are shown using black markers, $\mathrm{T\overline{T}}$ signals using solid lines, and background using filled histograms. Statistical and systematic uncertainties in the background prediction before performing the fit to data are shown by the hatched region. |
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Figure 2-a:
Distributions of DeepAK8 jet tags in the DeepAK8 CR (left), and ${H_{\mathrm {T}}}$ in the W+jets (center) and ${\mathrm{t} {}\mathrm{\bar{t}}}$ (right) CRs of the $\mathrm{T\overline{T}}$ search. The observed data are shown using black markers, $\mathrm{T\overline{T}}$ signals using solid lines, and background using filled histograms. Statistical and systematic uncertainties in the background prediction before performing the fit to data are shown by the hatched region. |
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Figure 2-b:
Distributions of DeepAK8 jet tags in the DeepAK8 CR (left), and ${H_{\mathrm {T}}}$ in the W+jets (center) and ${\mathrm{t} {}\mathrm{\bar{t}}}$ (right) CRs of the $\mathrm{T\overline{T}}$ search. The observed data are shown using black markers, $\mathrm{T\overline{T}}$ signals using solid lines, and background using filled histograms. Statistical and systematic uncertainties in the background prediction before performing the fit to data are shown by the hatched region. |
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Figure 2-c:
Distributions of DeepAK8 jet tags in the DeepAK8 CR (left), and ${H_{\mathrm {T}}}$ in the W+jets (center) and ${\mathrm{t} {}\mathrm{\bar{t}}}$ (right) CRs of the $\mathrm{T\overline{T}}$ search. The observed data are shown using black markers, $\mathrm{T\overline{T}}$ signals using solid lines, and background using filled histograms. Statistical and systematic uncertainties in the background prediction before performing the fit to data are shown by the hatched region. |
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Figure 3:
Distribution of lepton $p_T$ in 2017 (left) and 2018 (right) in the multilepton channel nonprompt lepton control region for all flavor categories, evaluated with the best-fit nonprompt rates. The uncertainty shown is the quadratic sum of statistical and systematics uncertainties. |
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Figure 3-a:
Distribution of lepton $p_T$ in 2017 (left) and 2018 (right) in the multilepton channel nonprompt lepton control region for all flavor categories, evaluated with the best-fit nonprompt rates. The uncertainty shown is the quadratic sum of statistical and systematics uncertainties. |
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Figure 3-b:
Distribution of lepton $p_T$ in 2017 (left) and 2018 (right) in the multilepton channel nonprompt lepton control region for all flavor categories, evaluated with the best-fit nonprompt rates. The uncertainty shown is the quadratic sum of statistical and systematics uncertainties. |
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Figure 4:
Distributions of the VLQ score in single-lepton categories 1-7 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 4-a:
Distributions of the VLQ score in single-lepton categories 1-7 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 4-b:
Distributions of the VLQ score in single-lepton categories 1-7 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 4-c:
Distributions of the VLQ score in single-lepton categories 1-7 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 4-d:
Distributions of the VLQ score in single-lepton categories 1-7 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 4-e:
Distributions of the VLQ score in single-lepton categories 1-7 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 4-f:
Distributions of the VLQ score in single-lepton categories 1-7 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 4-g:
Distributions of the VLQ score in single-lepton categories 1-7 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 5:
Distributions of the VLQ score in single-lepton categories 8-12 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 5-a:
Distributions of the VLQ score in single-lepton categories 8-12 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 5-b:
Distributions of the VLQ score in single-lepton categories 8-12 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 5-c:
Distributions of the VLQ score in single-lepton categories 8-12 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 5-d:
Distributions of the VLQ score in single-lepton categories 8-12 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 5-e:
Distributions of the VLQ score in single-lepton categories 8-12 (left-to-right, upper-to-lower). Observed data is shown using black markers, $\mathrm{T\overline{T}}$ signal with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. Electron and muon categories have been combined with their uncertainties added in quadrature. |
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Figure 6:
Distributions of ${H^{\mathrm {lep}}_{\mathrm {T}}}$ in the same-sign dilepton signal region for ee, e$ \mu $, and $\mu \mu $ categories (left-to-right). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 6-a:
Distributions of ${H^{\mathrm {lep}}_{\mathrm {T}}}$ in the same-sign dilepton signal region for ee, e$ \mu $, and $\mu \mu $ categories (left-to-right). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 6-b:
Distributions of ${H^{\mathrm {lep}}_{\mathrm {T}}}$ in the same-sign dilepton signal region for ee, e$ \mu $, and $\mu \mu $ categories (left-to-right). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 6-c:
Distributions of ${H^{\mathrm {lep}}_{\mathrm {T}}}$ in the same-sign dilepton signal region for ee, e$ \mu $, and $\mu \mu $ categories (left-to-right). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 7:
Distributions of ${S_\mathrm {T}}$ in the multilepton signal region for eee, ee$\mu$, e$\mu\mu$, and $\mu \mu \mu$ categories (left-to-right, upper-to-lower). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 7-a:
Distributions of ${S_\mathrm {T}}$ in the multilepton signal region for eee, ee$\mu$, e$\mu\mu$, and $\mu \mu \mu$ categories (left-to-right, upper-to-lower). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 7-b:
Distributions of ${S_\mathrm {T}}$ in the multilepton signal region for eee, ee$\mu$, e$\mu\mu$, and $\mu \mu \mu$ categories (left-to-right, upper-to-lower). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 7-c:
Distributions of ${S_\mathrm {T}}$ in the multilepton signal region for eee, ee$\mu$, e$\mu\mu$, and $\mu \mu \mu$ categories (left-to-right, upper-to-lower). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 7-d:
Distributions of ${S_\mathrm {T}}$ in the multilepton signal region for eee, ee$\mu$, e$\mu\mu$, and $\mu \mu \mu$ categories (left-to-right, upper-to-lower). Data from 2017 and 2018 is shown using black markers, $\mathrm{T\overline{T}}$ signals with mass of 1.2 (1.5) TeV in the singlet scenario using solid (dashed) lines, and post-fit background using filled histograms. Statistical and systematic uncertainties in the background prediction after performing the fit to data are shown by the hatched region. |
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Figure 8:
Expected 95% CL upper limits on $\mathrm{T\overline{T}}$ (upper) and $\mathrm{B\overline{B}}$ (lower) production cross sections for the singlet (left) and doublet (right) combinations. |
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Figure 8-a:
Expected 95% CL upper limits on $\mathrm{T\overline{T}}$ (upper) and $\mathrm{B\overline{B}}$ (lower) production cross sections for the singlet (left) and doublet (right) combinations. |
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Figure 8-b:
Expected 95% CL upper limits on $\mathrm{T\overline{T}}$ (upper) and $\mathrm{B\overline{B}}$ (lower) production cross sections for the singlet (left) and doublet (right) combinations. |
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Figure 8-c:
Expected 95% CL upper limits on $\mathrm{T\overline{T}}$ (upper) and $\mathrm{B\overline{B}}$ (lower) production cross sections for the singlet (left) and doublet (right) combinations. |
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Figure 8-d:
Expected 95% CL upper limits on $\mathrm{T\overline{T}}$ (upper) and $\mathrm{B\overline{B}}$ (lower) production cross sections for the singlet (left) and doublet (right) combinations. |
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Figure 9:
The 95% CL expected (left) and observed (right) lower limits on pair-produced T (upper) and B (lower) quark masses as a function of the branching ratios to W and H bosons. |
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Figure 9-a:
The 95% CL expected (left) and observed (right) lower limits on pair-produced T (upper) and B (lower) quark masses as a function of the branching ratios to W and H bosons. |
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Figure 9-b:
The 95% CL expected (left) and observed (right) lower limits on pair-produced T (upper) and B (lower) quark masses as a function of the branching ratios to W and H bosons. |
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Figure 9-c:
The 95% CL expected (left) and observed (right) lower limits on pair-produced T (upper) and B (lower) quark masses as a function of the branching ratios to W and H bosons. |
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Figure 9-d:
The 95% CL expected (left) and observed (right) lower limits on pair-produced T (upper) and B (lower) quark masses as a function of the branching ratios to W and H bosons. |
| Tables | |
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Table 1:
Numbers of predicted and observed CR events in 2016-2018 data for the $\mathrm{T\overline{T}}$ and $\mathrm{B\overline{B}}$ signal hypotheses in the single-lepton channel, after a background-only fit to data. Predicted numbers of signal events before the fit to data are included for comparison, using the singlet branching fraction scenario. Uncertainties include statistical and systematic components, and lepton flavor categories are combined with their uncertainties added in quadrature. Values in the DeepAK8 CR represent the number of large-radius jets rather than number of events. |
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Table 2:
Summary of systematic uncertainty sources for the various analysis channels, grouped according to channel. The second column shows uncertainties for the single-lepton channel, evaluated with 2016-2018 data combined. The third and fourth columns show uncertainties for the other channels, evaluated using 2017 or 2018 data. Ranges indicate representative values across different lepton flavor categories. Uncertainties that affect different sources are indicated as "MC'' for all simulation (including signal), "OS'' for charge misidentification background, and "NP'' for nonprompt lepton background. |
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Table 3:
Numbers of predicted and observed $\mathrm{T\overline{T}}$ SR events in 2016-2018 data in the single-lepton channel, after a background-only fit to data. Predicted numbers of signal events before the fit to data are included for comparison, using the singlet branching fraction scenario. Uncertainties include statistical and systematic components, and lepton flavor categories are combined with their uncertainties added in quadrature. |
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Table 4:
Numbers of predicted and observed $\mathrm{B\overline{B}}$ SR events in 2016-2018 data in the single-lepton channel, after a background-only fit to data. Predicted numbers of signal events before the fit to data are included for comparison, using the singlet branching fraction scenario. Uncertainties include statistical and systematic components, and lepton flavor categories are combined with their uncertainties added in quadrature. |
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Table 5:
Numbers of predicted and observed SR events in 2017-2018 data in the same-sign dilepton channel, after a background-only fit to data. Predicted numbers of signal events before the fit to data are included for comparison, using the singlet branching fraction scenario. Uncertainties include statistical and systematic components. Predictions for 2017 and 2018 are combined with their uncertainties added in quadrature. |
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Table 6:
Numbers of predicted and observed SR events in 2017-2018 data in the multilepton channel, after a background-only fit to data. Predicted numbers of signal events before the fit to data are included for comparison, using the singlet branching fraction scenario. Uncertainties include statistical and systematic components. Predictions for 2017 and 2018 are combined with their uncertainties added in quadrature. |
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Table 7:
Expected and observed lower limits on the T and B quark masses. |
| Summary |
| We have presented a search for vector-like $\mathrm{T}$ and $\mathrm{B}$ quark-antiquark pairs produced in proton-proton collisions at a center-of-mass energy of 13 TeV. Data collected by the CMS Experiment at the LHC in 2016-2018 have been analyzed in single-lepton, same-sign dilepton, and multilepton final states. In the single-lepton channel, parent particles of large-radius jets were identified using the DeepAK8 algorithm, and vector-like quark candidates were reconstructed by forming quark-boson pairs consistent with a $\mathrm{T}$ or $\mathrm{B}$ decay. To account for events without consistent vector-like quark decays, a multilayer perceptron network was trained to separate signal events from standard model backgrounds. In the same-sign dilepton and multilepton channels, low background rates and the large energy signature of the signal were exploited by studying jet and lepton momentum sum distributions. We exclude pair production for $\mathrm{T}$ quarks with masses up to 1.54 TeV and for $\mathrm{B}$ quarks with masses up to 1.56 TeV, depending on the branching fraction scenario. These are the strongest limits to date on $\mathrm{T\overline{T}}$ production with tH and bW decay modes and on $\mathrm{B}$ quark production where the $\mathrm{B}$ quark has a significant branching fraction to tW. |
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