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| CMS-EXO-21-019 ; CERN-EP-2023-301 | ||
| Search for pair production of scalar and vector leptoquarks decaying to muons and bottom quarks in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 9 February 2024 | ||
| Accepted for publication in Phys. Rev. D | ||
| Abstract: A search for pair production of scalar and vector leptoquarks (LQs) each decaying to a muon and a bottom quark is performed using proton-proton collision data collected at $ \sqrt{s}= $ 13 TeV with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. No excess above standard model expectation is observed. Scalar (vector) LQs with masses less than 1810 (2120) GeV are excluded at 95% confidence level, assuming a 100% branching fraction of the LQ decaying to a muon and a bottom quark. These limits represent the most stringent to date. | ||
| Links: e-print arXiv:2402.08668 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; Physics Briefing ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Dominant leading order Feynman diagrams for pair production of LQs at the LHC. |
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Figure 1-a:
Leading order Feynman diagram for pair production of LQs at the LHC. |
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Figure 1-b:
Leading order Feynman diagram for pair production of LQs at the LHC. |
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Figure 1-c:
Leading order Feynman diagram for pair production of LQs at the LHC. |
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Figure 1-d:
Leading order Feynman diagram for pair production of LQs at the LHC. |
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Figure 2:
Comparison of data and background $ m_{\mu\mu} $ distribution at the preselection level for the $ \mathrm{Z}/\gamma^* $+jets and $ \mathrm{t} \bar{\mathrm{t}} $+jets (left) and diboson and $ {\mathrm{t}\bar{\mathrm{t}}} \mathrm{V} $ (right) background control regions, with the corresponding data-to-background ratio shown below. For $ \mathrm{Z}/\gamma^* $+jets, the control region is a $ m_{\mu\mu} $ window of 80-100 GeV around the Z peak, and for $ \mathrm{t} \bar{\mathrm{t}} $ +jets is a window of 100-250 GeV. For diboson and $ {\mathrm{t}\bar{\mathrm{t}}} \mathrm{V} $ processes, the normalization is performed simultaneously, with a control region again of 80-100 GeV around the Z peak, but with a third lepton requirement (to remain orthogonal to the $ \mathrm{Z}/\gamma^* $+jets control region) and no b tag requirement (to diminish the statistical uncertainty). The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. The signal contribution in all control regions is negligible. |
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Figure 2-a:
Comparison of data and background $ m_{\mu\mu} $ distribution at the preselection level for the |
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Figure 2-b:
Comparison of data and background $ m_{\mu\mu} $ distribution at the preselection level for the $ \mathrm{Z}/\gamma^* $+jets and $ \mathrm{t} \bar{\mathrm{t}} $+jets (left) and diboson and $ {\mathrm{t}\bar{\mathrm{t}}} \mathrm{V} $ (right) background control regions, with the corresponding data-to-background ratio shown below. For $ \mathrm{Z}/\gamma^* $+jets, the control region is a $ m_{\mu\mu} $ window of 80-100 GeV around the Z peak, and for $ \mathrm{t} \bar{\mathrm{t}} $ +jets is a window of 100-250 GeV. For diboson and $ {\mathrm{t}\bar{\mathrm{t}}} \mathrm{V} $ processes, the normalization is performed simultaneously, with a control region again of 80-100 GeV around the Z peak, but with a third lepton requirement (to remain orthogonal to the $ \mathrm{Z}/\gamma^* $+jets control region) and no b tag requirement (to diminish the statistical uncertainty). The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. The signal contribution in all control regions is negligible. |
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Figure 3:
Comparison of data and background $ p_{\mathrm{T}} $ distribution at the preselection level for the leading two muons and jets. The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 3-a:
Comparison of data and background $ p_{\mathrm{T}} $ distribution at the preselection level for the leading two muons and jets. The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 3-b:
Comparison of data and background $ p_{\mathrm{T}} $ distribution at the preselection level for the leading two muons and jets. The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 3-c:
Comparison of data and background $ p_{\mathrm{T}} $ distribution at the preselection level for the leading two muons and jets. The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 3-d:
Comparison of data and background $ p_{\mathrm{T}} $ distribution at the preselection level for the leading two muons and jets. The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 4:
Comparison of data and background BDT discriminant distributions at the preselection level for LQ mass hypotheses of 1500 GeV (upper left), 1800 GeV (upper right), and 2000 GeV (lower). The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 4-a:
Comparison of data and background BDT discriminant distributions at the preselection level for LQ mass hypotheses of 1500 GeV (upper left), 1800 GeV (upper right), and 2000 GeV (lower). The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 4-b:
Comparison of data and background BDT discriminant distributions at the preselection level for LQ mass hypotheses of 1500 GeV (upper left), 1800 GeV (upper right), and 2000 GeV (lower). The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 4-c:
Comparison of data and background BDT discriminant distributions at the preselection level for LQ mass hypotheses of 1500 GeV (upper left), 1800 GeV (upper right), and 2000 GeV (lower). The error bars are the data statistical uncertainties, while the shaded band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 5:
Total signal selection efficiency, defined as the number of events passing the final selection divided by the number of generated events. The discrete nature of the individual BDT training and final selection for each LQ candidate mass produces the observed variation in the efficiency. Relative uncertainties are less than one percent in all cases. |
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Figure 6:
Data, background, and signal event yields after final selections, for each scalar $ m_{\mathrm{LQ}} $ hypothesis. Each bin on the $ y $ axis represents an independent $ m_{\mathrm{LQ}} $ hypothesis. The hatched band represents the combined statistical and systematic uncertainty in the full background estimate. |
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Figure 7:
The expected and observed upper limits at 95% CL on the product of the LQ pair production cross section and the branching fractions $ \beta^2 $ as a function of $ m_{\mathrm{LQ}} $. The black solid line represents the observed limits, the dotted line is for the median expected limits, and the inner dark-green and outer light-yellow bands are for the 68 and 95% CL intervals. The solid blue line and corresponding blue band represents the theoretical scalar LQ pair production cross sections and the uncertainties on the cross sections due to the PDF prediction and renormalization and factorization scales, respectively. Similarly, the dash-dotted (dashed) line and corresponding band represents the cross sections of theoretical vector LQ pair production and uncertainties in the minimal coupling (Yang-Mills) scenario. |
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Figure 8:
The expected and observed exclusion limits at 95% CL as a function of the leptoquark mass and the branching fraction $ \beta $. The solid line represents the observed limits, the dashed line represents the median expected limits, and the inner dark-green and outer light-yellow bands represent the 68 and 95% CL intervals. The area left of the observed limit is excluded. |
| Tables | |
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Table 1:
Systematic uncertainties in signal efficiency and background yields in the combined 2016-2018 data set, shown as a range over all final selections (second and third columns) as well as for the $ m_{\mathrm{LQ}} = $ 1800 GeV point (rightmost two columns). The last two rows show the total systematic and statistical uncertainties in the simulated samples. |
| Summary |
| A search has been performed for pair production of leptoquarks (LQs) decaying to muons and bottom quarks using proton-proton collision data collected at $ \sqrt{s} = $ 13 TeV in 2016-2018 with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. Limits are set at 95% confidence level on the product of the scalar LQ pair production cross section and $ \beta^2 $, as a function of the LQ mass $ m_{\mathrm{LQ}} $, where $ \beta $ is the branching fraction of the LQ decaying to a muon and a bottom quark. Scalar LQs with $ m_{\mathrm{LQ}} < $ 1810 GeV are excluded for $ \beta= $ 1. The results are also presented as a function of $ \beta $, and scalar LQs with $ m_{\mathrm{LQ}} < $ 1540 GeV are excluded for $ \beta= $ 0.5. A further interpretation is performed with a vector LQ model, and vector LQs with $ m_{\mathrm{LQ}} < $ 2120 (2460) GeV are excluded in the minimal coupling (Yang-Mills) scenario for $ \beta= $ 1. These represent the most stringent limits to date on these models. |
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