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| CMS-B2G-24-013 ; CERN-EP-2026-137 | ||
| Search for single production of a vector-like $ {\mathrm{B}}^{\prime}$ quark decaying to a top quark and a W boson in the single-lepton final state in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 31 May 2026 | ||
| Submitted to Physical Review D | ||
| Abstract: A search is presented for the single production of a narrow-width vector-like $ {\mathrm{B}}^{\prime}$ quark that decays to a t quark and a W boson, with one of the decay products yielding an electron or muon. The data were collected from 2016 to 2018 by the CMS experiment at the LHC in proton-proton collisions at $ \sqrt{s}= $ 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The search is performed in a single-lepton final state, where the $ {\mathrm{B}}^{\prime}$ quark candidate is reconstructed from an electron or muon, missing transverse momentum, one large-radius jet, and one small-radius jet if the t quark decays leptonically. The originating particles of large-radius jets are identified using a neural-network-based tagger, and the dominant background contributions are modeled from data using a neural autoregressive flow network. This search is the most sensitive to date to the single production of narrow-width $ {\mathrm{B}}^{\prime}$ quarks, excluding singlet $ {\mathrm{B}}^{\prime}$ quarks with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $ for masses between 0.8 and 1.23 TeV. Limits are also placed on the production cross section of single $ {\mathrm{B}}^{\prime}$ quarks produced in association with t quarks, and on the coupling factor of the $ {\mathrm{B}}^{\prime}$ quark to electroweak bosons. | ||
| Links: e-print arXiv:2606.01423 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Tree-level Feynman diagram showing the single production of a $ {\mathrm{B}}^{\prime}$ quark in association with an SM b quark or t quark, decaying in the $ \mathrm{t}\mathrm{W} $ channel. |
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Figure 2:
Distributions of the reconstructed $ {\mathrm{B}}^{\prime}$ quark mass, $ m_{\mathrm{t}\mathrm{W}} $ (upper left), the scalar $ p_{\mathrm{T}} $ sum ($ S_\mathrm{T} $) of small-radius jets, lepton, and $ p_{\mathrm{T}}^\text{miss} $ (upper right), and the reconstruction case (lower) for all selected events. The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to a cross section of 1 pb for visualization. Simulated background estimates are displayed as filled histograms. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 2-a:
Distributions of the reconstructed $ {\mathrm{B}}^{\prime}$ quark mass, $ m_{\mathrm{t}\mathrm{W}} $ (upper left), the scalar $ p_{\mathrm{T}} $ sum ($ S_\mathrm{T} $) of small-radius jets, lepton, and $ p_{\mathrm{T}}^\text{miss} $ (upper right), and the reconstruction case (lower) for all selected events. The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to a cross section of 1 pb for visualization. Simulated background estimates are displayed as filled histograms. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 2-b:
Distributions of the reconstructed $ {\mathrm{B}}^{\prime}$ quark mass, $ m_{\mathrm{t}\mathrm{W}} $ (upper left), the scalar $ p_{\mathrm{T}} $ sum ($ S_\mathrm{T} $) of small-radius jets, lepton, and $ p_{\mathrm{T}}^\text{miss} $ (upper right), and the reconstruction case (lower) for all selected events. The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to a cross section of 1 pb for visualization. Simulated background estimates are displayed as filled histograms. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 2-c:
Distributions of the reconstructed $ {\mathrm{B}}^{\prime}$ quark mass, $ m_{\mathrm{t}\mathrm{W}} $ (upper left), the scalar $ p_{\mathrm{T}} $ sum ($ S_\mathrm{T} $) of small-radius jets, lepton, and $ p_{\mathrm{T}}^\text{miss} $ (upper right), and the reconstruction case (lower) for all selected events. The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to a cross section of 1 pb for visualization. Simulated background estimates are displayed as filled histograms. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 3:
Distributions of b-tagged jet multiplicity (left) and forward jet multiplicity (right) for all selected events. The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to a cross section of 1 pb for visualization. Simulated background estimates are displayed as filled histograms. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 3-a:
Distributions of b-tagged jet multiplicity (left) and forward jet multiplicity (right) for all selected events. The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to a cross section of 1 pb for visualization. Simulated background estimates are displayed as filled histograms. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 3-b:
Distributions of b-tagged jet multiplicity (left) and forward jet multiplicity (right) for all selected events. The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to a cross section of 1 pb for visualization. Simulated background estimates are displayed as filled histograms. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 4:
Diagrams illustrating the definitions and labels of the CRs and SR (left), and the subsets of the SR used for validation (right). |
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Figure 5:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ in the SR and CRs for the lepW ABCDnn model, normalized to unity. Observed data are shown as black markers with statistical uncertainties. Major background distributions from simulation are shown as orange solid lines with statistical uncertainties and are labeled ``MC''. The ABCDnn predictions are shown as blue filled histograms. The lower panels show the ratio of the data to the ABCDnn prediction. Statistical and training uncertainties in the ABCDnn predictions are indicated by hatched bands, though they are too small to be visible in the upper panels. |
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Figure 6:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ in the SR and CRs for the lepT ABCDnn model, normalized to unity. Observed data are shown as black markers with statistical uncertainties. Major background distributions from simulation are shown as orange solid lines with statistical uncertainties and are labeled ``MC''. The ABCDnn predictions are shown as blue filled histograms. The lower panels show the ratio of the data to the ABCDnn prediction. Statistical and training uncertainties in the ABCDnn predictions are indicated by hatched bands, though they are too small to be visible in the upper panels. |
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Figure 7:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for VR events in Case 1 (upper left) through Case 4 (lower right). Observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. Background estimates are displayed as filled histograms, with the ABCDnn prediction shown prior to application of the closure correction. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 7-a:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for VR events in Case 1 (upper left) through Case 4 (lower right). Observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. Background estimates are displayed as filled histograms, with the ABCDnn prediction shown prior to application of the closure correction. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 7-b:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for VR events in Case 1 (upper left) through Case 4 (lower right). Observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. Background estimates are displayed as filled histograms, with the ABCDnn prediction shown prior to application of the closure correction. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 7-c:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for VR events in Case 1 (upper left) through Case 4 (lower right). Observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. Background estimates are displayed as filled histograms, with the ABCDnn prediction shown prior to application of the closure correction. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 7-d:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for VR events in Case 1 (upper left) through Case 4 (lower right). Observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. Background estimates are displayed as filled histograms, with the ABCDnn prediction shown prior to application of the closure correction. The lower panels show the ratio of the data to the background prediction. Statistical and systematic uncertainties in the background estimate are indicated by hatched bands. |
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Figure 8:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for events in the SR in Case 1 (upper left) through Case 4 (lower right). The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as the solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. The best-fit background prediction from a background-only fit to data is shown as the filled histograms. The lower panels show the difference between the data and the background prediction, divided by the total uncertainty in the background estimate. |
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Figure 8-a:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for events in the SR in Case 1 (upper left) through Case 4 (lower right). The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as the solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. The best-fit background prediction from a background-only fit to data is shown as the filled histograms. The lower panels show the difference between the data and the background prediction, divided by the total uncertainty in the background estimate. |
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Figure 8-b:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for events in the SR in Case 1 (upper left) through Case 4 (lower right). The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as the solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. The best-fit background prediction from a background-only fit to data is shown as the filled histograms. The lower panels show the difference between the data and the background prediction, divided by the total uncertainty in the background estimate. |
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Figure 8-c:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for events in the SR in Case 1 (upper left) through Case 4 (lower right). The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as the solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. The best-fit background prediction from a background-only fit to data is shown as the filled histograms. The lower panels show the difference between the data and the background prediction, divided by the total uncertainty in the background estimate. |
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Figure 8-d:
Distributions of $ m_{\mathrm{t}\mathrm{W}} $ for events in the SR in Case 1 (upper left) through Case 4 (lower right). The observed data are shown as black markers. Predicted $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ quark signals with masses of 1.0 and 1.4 TeV are shown as the solid and dashed lines, respectively, normalized to the predicted cross section for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production with $ \Gamma/m_{{\mathrm{B}}^{\prime}} =5% $. The best-fit background prediction from a background-only fit to data is shown as the filled histograms. The lower panels show the difference between the data and the background prediction, divided by the total uncertainty in the background estimate. |
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Figure 9:
Observed (solid black lines) and expected (dashed lines) 95% CL upper limits on the product of the production cross section and branching fraction $ \mathcal{B}(\mathrm{t}\mathrm{W}) $ for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production (upper), singlet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower left), and up-type doublet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower right), as functions of $ m_{{\mathrm{B}}^{\prime}} $. Predicted cross sections for various $ {\mathrm{B}}^{\prime}$ quark relative widths are shown as dashed red and solid blue lines. The bands around the predicted cross sections represent the associated energy scale and PDF uncertainties. |
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Figure 9-a:
Observed (solid black lines) and expected (dashed lines) 95% CL upper limits on the product of the production cross section and branching fraction $ \mathcal{B}(\mathrm{t}\mathrm{W}) $ for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production (upper), singlet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower left), and up-type doublet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower right), as functions of $ m_{{\mathrm{B}}^{\prime}} $. Predicted cross sections for various $ {\mathrm{B}}^{\prime}$ quark relative widths are shown as dashed red and solid blue lines. The bands around the predicted cross sections represent the associated energy scale and PDF uncertainties. |
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Figure 9-b:
Observed (solid black lines) and expected (dashed lines) 95% CL upper limits on the product of the production cross section and branching fraction $ \mathcal{B}(\mathrm{t}\mathrm{W}) $ for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production (upper), singlet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower left), and up-type doublet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower right), as functions of $ m_{{\mathrm{B}}^{\prime}} $. Predicted cross sections for various $ {\mathrm{B}}^{\prime}$ quark relative widths are shown as dashed red and solid blue lines. The bands around the predicted cross sections represent the associated energy scale and PDF uncertainties. |
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Figure 9-c:
Observed (solid black lines) and expected (dashed lines) 95% CL upper limits on the product of the production cross section and branching fraction $ \mathcal{B}(\mathrm{t}\mathrm{W}) $ for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production (upper), singlet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower left), and up-type doublet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower right), as functions of $ m_{{\mathrm{B}}^{\prime}} $. Predicted cross sections for various $ {\mathrm{B}}^{\prime}$ quark relative widths are shown as dashed red and solid blue lines. The bands around the predicted cross sections represent the associated energy scale and PDF uncertainties. |
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Figure 10:
Observed (solid black lines) and expected (dashed lines) 95% CL upper limits on the coupling factor $ \kappa $ for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production (upper), singlet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower left), and up-type doublet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower right), as functions of $ m_{{\mathrm{B}}^{\prime}} $. The hatched and shaded regions indicate that the limits are upper bounds on the coupling factor. Predicted coupling values for various $ {\mathrm{B}}^{\prime}$ quark relative widths are shown as dashed red, solid blue, and dotted magenta lines. |
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Figure 10-a:
Observed (solid black lines) and expected (dashed lines) 95% CL upper limits on the coupling factor $ \kappa $ for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production (upper), singlet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower left), and up-type doublet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower right), as functions of $ m_{{\mathrm{B}}^{\prime}} $. The hatched and shaded regions indicate that the limits are upper bounds on the coupling factor. Predicted coupling values for various $ {\mathrm{B}}^{\prime}$ quark relative widths are shown as dashed red, solid blue, and dotted magenta lines. |
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Figure 10-b:
Observed (solid black lines) and expected (dashed lines) 95% CL upper limits on the coupling factor $ \kappa $ for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production (upper), singlet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower left), and up-type doublet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower right), as functions of $ m_{{\mathrm{B}}^{\prime}} $. The hatched and shaded regions indicate that the limits are upper bounds on the coupling factor. Predicted coupling values for various $ {\mathrm{B}}^{\prime}$ quark relative widths are shown as dashed red, solid blue, and dotted magenta lines. |
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Figure 10-c:
Observed (solid black lines) and expected (dashed lines) 95% CL upper limits on the coupling factor $ \kappa $ for singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production (upper), singlet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower left), and up-type doublet $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production (lower right), as functions of $ m_{{\mathrm{B}}^{\prime}} $. The hatched and shaded regions indicate that the limits are upper bounds on the coupling factor. Predicted coupling values for various $ {\mathrm{B}}^{\prime}$ quark relative widths are shown as dashed red, solid blue, and dotted magenta lines. |
| Tables | |
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Table 1:
Values of $ \hat{\sigma}_{\mathrm{NWA}} $ and $ \kappa $ used to compute the cross sections for the production of a $ {\mathrm{B}}^{\prime}$ quark that is either a singlet or a member of a (\HepParticle{\HepParticleT} {\prime},\HepParticle $ {\mathrm{B}}^{\prime}$ ) doublet, based on the calculations described in Refs. [none-none-none,35]. The value of $ \hat{\sigma}_{\mathrm{NWA}} $ depends on the $ {\mathrm{B}}^{\prime}$ quark mass and production mode. The value of $ \kappa $ depends on the $ {\mathrm{B}}^{\prime}$ quark mass, width, and multiplet structure. All numerical values are rounded to two significant figures, and uncertainties due to renormalization and factorization scales are provided for $ \hat{\sigma}_{\mathrm{NWA}} $. |
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Table 2:
The ABCDnn architectures and RBF kernel sizes for the lepW and lepT models. The lepW model is trained on events in reconstruction Cases 1 and 4, and the lepT model is trained on events in reconstruction Cases 2 and 3. |
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Table 3:
A summary of the systematic uncertainties impacting the analysis. Unless otherwise specified, all uncertainties are implemented as rate and shape variations using alternate template histograms. The numerical values represent the prefit rate impact and are given as ranges across the four reconstruction cases for either the 1.4 TeV signal or the ABCDnn background prediction, unless otherwise specified. The functional form in the third column indicates the quantities on which the uncertainty magnitude depends, where $ \textrm{s.d.} $ denotes one standard deviation. The final column indicates the affected predictions: simulated samples (including signal), ``minor'' refers to simulated minor background processes, and ``ABCDnn'' refers to the major background predicted using the ABCDnn method. |
| Summary |
| A search has been presented for the single production of a vector-like $ {\mathrm{B}}^{\prime}$ quark that decays to a t quark and a W boson via the electroweak interaction. Proton-proton collision data collected with the CMS detector at a center-of-mass energy of 13 TeV are used, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. Events are selected with one electron or muon, missing transverse momentum, and at least one large-radius jet well separated from the charged lepton. A $ {\mathrm{B}}^{\prime}$ quark candidate is reconstructed and categorized according to the PARTICLENET identification of the large-radius jet. Minor background processes are modeled using simulation, while the major background contribution in the signal region is modeled from data in five control regions using a neural autoregressive flow network, referred to as ABCDnn. For $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production, singlet $ {\mathrm{B}}^{\prime}$ quarks with a 5% relative decay width and masses between 0.8 and 1.23 TeV are excluded at 95% confidence level (CL). Limits are also set on the product of the single production cross section and the ${{\mathrm{B}}}{\prime} \to\mathrm{t}\mathrm{W} $ branching fraction for $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production, excluding the 0.9 and 1.0 TeV mass hypotheses at 95% CL for both the 5%-width singlet and 1%-width doublet scenarios. For singlet $ \mathrm{b}\mathrm{q}{\mathrm{B}}^{\prime} $ production, coupling factor values above 0.30 are excluded for $ {\mathrm{B}}^{\prime}$ quark masses in the range 0.8--1.8 TeV. For $ \mathrm{t}\mathrm{q}{\mathrm{B}}^{\prime} $ production, coupling factor values above 0.41 are excluded at 95% CL for singlet $ {\mathrm{B}}^{\prime}$ quark masses in the range 0.8--1.2 TeV, and values above 0.29 are excluded at 95% CL for doublet $ {\mathrm{B}}^{\prime}$ quark masses in the range 0.8--2.0 TeV. These limits are the most stringent to date for the single production cross section and coupling factors of narrow-width $ {\mathrm{B}}^{\prime}$ quarks. |
| Additional Figures | |
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Additional Figure 1:
Distributions of $S_\mathrm{T}$ in the SR and CRs for the lepW ABCDnn model, normalized to unity. The last bins are overflow bins with all the contributions from bins with $S_\mathrm{T}>1500$ GeV. Observed data are shown as black markers with statistical uncertainties. Major background distributions from simulation are shown as orange solid lines with statistical uncertainties and are labeled ``MC''. ABCDnn predictions are shown as blue filled histograms. Statistical and training uncertainties in the ABCDnn predictions are indicated by hatched bands, though they are too small to be visible in the upper panels. The lower panels show the ratio of the data to the ABCDnn prediction. The disagreement between data and predicted shapes is generally within 20% in the CRs and is greater in the SR. |
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Additional Figure 2:
Distributions of $S_\mathrm{T}$ in the SR and CRs for the lepT ABCDnn model, normalized to unity. The last bins are overflow bins with all the contributions from bins with $S_\mathrm{T}>1500$ GeV. Observed data are shown as black markers with statistical uncertainties. Major background distributions from simulation are shown as orange solid lines with statistical uncertainties and are labeled ``MC''. ABCDnn predictions are shown as blue filled histograms. Statistical and training uncertainties in the ABCDnn predictions are indicated by hatched bands, though they are too small to be visible in the upper panels. The lower panels show the ratio of the data to the ABCDnn prediction. Disagreement between data and predicted distributions is within 10% for most of the range that is relevant to the analysis in all regions. The largest deviations are around 20% and mainly occur in the tails of some CRs, where the statistics are low. The performance is stable across the training regions (CRs) and the application region (SR). |
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Additional Figure 3:
Upper limits at 95% CL on the single production cross section of singlet B quarks that are produced in association with a b quark (upper) or a t quark (lower), as a function of the B quark mass. Expected limits are shown in dashed lines and observed limits in solid lines. Theoretical predictions for B quarks with relative widths of 1% and 5% are overlaid in gray solid lines. The limits are obtained in searches by CMS with integrated luminosities of 36 fb$ ^{-1} $(denoted by the clubs symbol) and 138 fb$ ^{-1} $ Final states and publication references are noted in the legends. |
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Additional Figure 3-a:
Upper limits at 95% CL on the single production cross section of singlet B quarks that are produced in association with a b quark (upper) or a t quark (lower), as a function of the B quark mass. Expected limits are shown in dashed lines and observed limits in solid lines. Theoretical predictions for B quarks with relative widths of 1% and 5% are overlaid in gray solid lines. The limits are obtained in searches by CMS with integrated luminosities of 36 fb$ ^{-1} $(denoted by the clubs symbol) and 138 fb$ ^{-1} $ Final states and publication references are noted in the legends. |
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Additional Figure 3-b:
Upper limits at 95% CL on the single production cross section of singlet B quarks that are produced in association with a b quark (upper) or a t quark (lower), as a function of the B quark mass. Expected limits are shown in dashed lines and observed limits in solid lines. Theoretical predictions for B quarks with relative widths of 1% and 5% are overlaid in gray solid lines. The limits are obtained in searches by CMS with integrated luminosities of 36 fb$ ^{-1} $(denoted by the clubs symbol) and 138 fb$ ^{-1} $ Final states and publication references are noted in the legends. |
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