CMS-TOP-22-005 ; CERN-EP-2023-258 | ||
Search for charged-lepton flavor violation in the production and decay of top quarks using trilepton final states in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | ||
CMS Collaboration | ||
5 December 2023 | ||
Submitted to Phys. Rev. D | ||
Abstract: A search is performed for charged-lepton flavor violating processes in top quark (t) production and decay. The data were collected by the CMS experiment from proton-proton collisions at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb$ ^{-1} $. The selected events are required to contain one opposite-sign electron-muon pair, a third charged lepton (electron or muon), and at least one jet of which no more than one is associated with a bottom quark. Boosted decision trees are used to distinguish signal from background, exploiting differences in the kinematics of the final states particles. The data are consistent with the standard model expectation. Upper limits at 95% confidence level are placed in the context of effective field theory on the Wilson coefficients, which range between 0.024-0.424 TeV$^{-2}$ depending on the flavor of the associated light quark and the Lorentz structure of the interaction. These limits are converted to upper limits on branching fractions involving up (charm) quarks, $ \mathrm{t}\to\mathrm{e}\mu\mathrm{u} $ ($ \mathrm{t}\to\mathrm{e}\mu\mathrm{c} $), of 0.032 (0.498) $\times$10$^{-6} $, 0.022 (0.369) $\times$10$^{-6} $, and 0.012 (0.216) $\times$10$^{-6} $ for tensor-like, vector-like, and scalar-like interactions, respectively. | ||
Links: e-print arXiv:2312.03199 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
Representative Feynman diagrams for the signal processes that are targeted by this analysis. Both top quark decay (left) and production (middle and right) CLFV processes are shown. The CLFV interaction vertex is shown as a solid red circle to indicate that it is not allowed in the SM. |
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Figure 1-a:
Representative Feynman diagrams for the signal processes that are targeted by this analysis. Both top quark decay (left) and production (middle and right) CLFV processes are shown. The CLFV interaction vertex is shown as a solid red circle to indicate that it is not allowed in the SM. |
png pdf |
Figure 1-b:
Representative Feynman diagrams for the signal processes that are targeted by this analysis. Both top quark decay (left) and production (middle and right) CLFV processes are shown. The CLFV interaction vertex is shown as a solid red circle to indicate that it is not allowed in the SM. |
png pdf |
Figure 1-c:
Representative Feynman diagrams for the signal processes that are targeted by this analysis. Both top quark decay (left) and production (middle and right) CLFV processes are shown. The CLFV interaction vertex is shown as a solid red circle to indicate that it is not allowed in the SM. |
png pdf |
Figure 2:
Distributions of the leading lepton $ \eta $ (left column) and the jet multiplicity (right column) in the nonprompt VRs. Events in the $ \mathrm{e}\mathrm{e}\mathrm{e} $, $ \mathrm{e}\mu\ell $, and $ \mu\mu\mu $ nonprompt VRs are shown in the upper, middle, and lower row, respectively. The data are shown as filled points and the SM background predictions as histograms. The VV(V) background includes ZZ and triboson production, while the $ \mathrm{t}(\bar{\mathrm{t}})+\mathrm{X(X)} $ component includes $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{W} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{H} $, $ \mathrm{t}\mathrm{Z}\mathrm{q} $, and smaller backgrounds containing one or two top quarks plus a boson or quark. The nonprompt background is estimated using control samples in data, while other backgrounds are estimated using MC simulation. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of the right column histograms includes the overflow events. |
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Figure 2-a:
Distributions of the leading lepton $ \eta $ (left column) and the jet multiplicity (right column) in the nonprompt VRs. Events in the $ \mathrm{e}\mathrm{e}\mathrm{e} $, $ \mathrm{e}\mu\ell $, and $ \mu\mu\mu $ nonprompt VRs are shown in the upper, middle, and lower row, respectively. The data are shown as filled points and the SM background predictions as histograms. The VV(V) background includes ZZ and triboson production, while the $ \mathrm{t}(\bar{\mathrm{t}})+\mathrm{X(X)} $ component includes $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{W} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{H} $, $ \mathrm{t}\mathrm{Z}\mathrm{q} $, and smaller backgrounds containing one or two top quarks plus a boson or quark. The nonprompt background is estimated using control samples in data, while other backgrounds are estimated using MC simulation. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of the right column histograms includes the overflow events. |
png pdf |
Figure 2-b:
Distributions of the leading lepton $ \eta $ (left column) and the jet multiplicity (right column) in the nonprompt VRs. Events in the $ \mathrm{e}\mathrm{e}\mathrm{e} $, $ \mathrm{e}\mu\ell $, and $ \mu\mu\mu $ nonprompt VRs are shown in the upper, middle, and lower row, respectively. The data are shown as filled points and the SM background predictions as histograms. The VV(V) background includes ZZ and triboson production, while the $ \mathrm{t}(\bar{\mathrm{t}})+\mathrm{X(X)} $ component includes $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{W} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{H} $, $ \mathrm{t}\mathrm{Z}\mathrm{q} $, and smaller backgrounds containing one or two top quarks plus a boson or quark. The nonprompt background is estimated using control samples in data, while other backgrounds are estimated using MC simulation. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of the right column histograms includes the overflow events. |
png pdf |
Figure 2-c:
Distributions of the leading lepton $ \eta $ (left column) and the jet multiplicity (right column) in the nonprompt VRs. Events in the $ \mathrm{e}\mathrm{e}\mathrm{e} $, $ \mathrm{e}\mu\ell $, and $ \mu\mu\mu $ nonprompt VRs are shown in the upper, middle, and lower row, respectively. The data are shown as filled points and the SM background predictions as histograms. The VV(V) background includes ZZ and triboson production, while the $ \mathrm{t}(\bar{\mathrm{t}})+\mathrm{X(X)} $ component includes $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{W} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{H} $, $ \mathrm{t}\mathrm{Z}\mathrm{q} $, and smaller backgrounds containing one or two top quarks plus a boson or quark. The nonprompt background is estimated using control samples in data, while other backgrounds are estimated using MC simulation. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of the right column histograms includes the overflow events. |
png pdf |
Figure 2-d:
Distributions of the leading lepton $ \eta $ (left column) and the jet multiplicity (right column) in the nonprompt VRs. Events in the $ \mathrm{e}\mathrm{e}\mathrm{e} $, $ \mathrm{e}\mu\ell $, and $ \mu\mu\mu $ nonprompt VRs are shown in the upper, middle, and lower row, respectively. The data are shown as filled points and the SM background predictions as histograms. The VV(V) background includes ZZ and triboson production, while the $ \mathrm{t}(\bar{\mathrm{t}})+\mathrm{X(X)} $ component includes $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{W} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{H} $, $ \mathrm{t}\mathrm{Z}\mathrm{q} $, and smaller backgrounds containing one or two top quarks plus a boson or quark. The nonprompt background is estimated using control samples in data, while other backgrounds are estimated using MC simulation. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of the right column histograms includes the overflow events. |
png pdf |
Figure 2-e:
Distributions of the leading lepton $ \eta $ (left column) and the jet multiplicity (right column) in the nonprompt VRs. Events in the $ \mathrm{e}\mathrm{e}\mathrm{e} $, $ \mathrm{e}\mu\ell $, and $ \mu\mu\mu $ nonprompt VRs are shown in the upper, middle, and lower row, respectively. The data are shown as filled points and the SM background predictions as histograms. The VV(V) background includes ZZ and triboson production, while the $ \mathrm{t}(\bar{\mathrm{t}})+\mathrm{X(X)} $ component includes $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{W} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{H} $, $ \mathrm{t}\mathrm{Z}\mathrm{q} $, and smaller backgrounds containing one or two top quarks plus a boson or quark. The nonprompt background is estimated using control samples in data, while other backgrounds are estimated using MC simulation. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of the right column histograms includes the overflow events. |
png pdf |
Figure 2-f:
Distributions of the leading lepton $ \eta $ (left column) and the jet multiplicity (right column) in the nonprompt VRs. Events in the $ \mathrm{e}\mathrm{e}\mathrm{e} $, $ \mathrm{e}\mu\ell $, and $ \mu\mu\mu $ nonprompt VRs are shown in the upper, middle, and lower row, respectively. The data are shown as filled points and the SM background predictions as histograms. The VV(V) background includes ZZ and triboson production, while the $ \mathrm{t}(\bar{\mathrm{t}})+\mathrm{X(X)} $ component includes $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{W} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $, $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{H} $, $ \mathrm{t}\mathrm{Z}\mathrm{q} $, and smaller backgrounds containing one or two top quarks plus a boson or quark. The nonprompt background is estimated using control samples in data, while other backgrounds are estimated using MC simulation. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of the right column histograms includes the overflow events. |
png pdf |
Figure 3:
Distributions of kinematic variables in the SR: LFV electron $ p_{\mathrm{T}} $ (upper left), LFV muon $ p_{\mathrm{T}} $ (upper right), LFV $ \mathrm{e}\mu $ mass (middle left), LFV top quark mass (middle right), OSSF lepton pair mass (lower left), and b jet multiplicity (lower right). The CLFV top quark decay and production signals are shown as dotted red and solid purple lines, respectively. The original signal normalization, corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of all but the lower-right histogram includes the overflow events. |
png pdf |
Figure 3-a:
Distributions of kinematic variables in the SR: LFV electron $ p_{\mathrm{T}} $ (upper left), LFV muon $ p_{\mathrm{T}} $ (upper right), LFV $ \mathrm{e}\mu $ mass (middle left), LFV top quark mass (middle right), OSSF lepton pair mass (lower left), and b jet multiplicity (lower right). The CLFV top quark decay and production signals are shown as dotted red and solid purple lines, respectively. The original signal normalization, corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of all but the lower-right histogram includes the overflow events. |
png pdf |
Figure 3-b:
Distributions of kinematic variables in the SR: LFV electron $ p_{\mathrm{T}} $ (upper left), LFV muon $ p_{\mathrm{T}} $ (upper right), LFV $ \mathrm{e}\mu $ mass (middle left), LFV top quark mass (middle right), OSSF lepton pair mass (lower left), and b jet multiplicity (lower right). The CLFV top quark decay and production signals are shown as dotted red and solid purple lines, respectively. The original signal normalization, corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of all but the lower-right histogram includes the overflow events. |
png pdf |
Figure 3-c:
Distributions of kinematic variables in the SR: LFV electron $ p_{\mathrm{T}} $ (upper left), LFV muon $ p_{\mathrm{T}} $ (upper right), LFV $ \mathrm{e}\mu $ mass (middle left), LFV top quark mass (middle right), OSSF lepton pair mass (lower left), and b jet multiplicity (lower right). The CLFV top quark decay and production signals are shown as dotted red and solid purple lines, respectively. The original signal normalization, corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of all but the lower-right histogram includes the overflow events. |
png pdf |
Figure 3-d:
Distributions of kinematic variables in the SR: LFV electron $ p_{\mathrm{T}} $ (upper left), LFV muon $ p_{\mathrm{T}} $ (upper right), LFV $ \mathrm{e}\mu $ mass (middle left), LFV top quark mass (middle right), OSSF lepton pair mass (lower left), and b jet multiplicity (lower right). The CLFV top quark decay and production signals are shown as dotted red and solid purple lines, respectively. The original signal normalization, corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of all but the lower-right histogram includes the overflow events. |
png pdf |
Figure 3-e:
Distributions of kinematic variables in the SR: LFV electron $ p_{\mathrm{T}} $ (upper left), LFV muon $ p_{\mathrm{T}} $ (upper right), LFV $ \mathrm{e}\mu $ mass (middle left), LFV top quark mass (middle right), OSSF lepton pair mass (lower left), and b jet multiplicity (lower right). The CLFV top quark decay and production signals are shown as dotted red and solid purple lines, respectively. The original signal normalization, corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of all but the lower-right histogram includes the overflow events. |
png pdf |
Figure 3-f:
Distributions of kinematic variables in the SR: LFV electron $ p_{\mathrm{T}} $ (upper left), LFV muon $ p_{\mathrm{T}} $ (upper right), LFV $ \mathrm{e}\mu $ mass (middle left), LFV top quark mass (middle right), OSSF lepton pair mass (lower left), and b jet multiplicity (lower right). The CLFV top quark decay and production signals are shown as dotted red and solid purple lines, respectively. The original signal normalization, corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. The last bin of all but the lower-right histogram includes the overflow events. |
png pdf |
Figure 4:
Distributions of the BDT discriminant targeting the CLFV top quark decay (left) and production (right) signal. Contributions from the two signal modes (production and decay) are combined within each SR and are shown as the solid red line. The pre-fit signal strength ($ \mu_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}= $ 1), corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. |
png pdf |
Figure 4-a:
Distributions of the BDT discriminant targeting the CLFV top quark decay (left) and production (right) signal. Contributions from the two signal modes (production and decay) are combined within each SR and are shown as the solid red line. The pre-fit signal strength ($ \mu_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}= $ 1), corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. |
png pdf |
Figure 4-b:
Distributions of the BDT discriminant targeting the CLFV top quark decay (left) and production (right) signal. Contributions from the two signal modes (production and decay) are combined within each SR and are shown as the solid red line. The pre-fit signal strength ($ \mu_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}= $ 1), corresponding to $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is scaled up (down) by a factor of 3 (20) for the CLFV top quark decay (production) signal for better visualization. The hatched bands indicate statistical and systematic uncertainties in the background predictions. |
png pdf |
Figure 5:
Distributions of the post-fit BDT discriminant targeting the CLFV top quark decay (left) and production (right) signal. Contributions from the two signal modes (production and decay) are combined within each SR and are shown as the solid red line. The post-fit signal strength ($ \mu_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}=\hat{\mu}_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}} $) is used to normalize the signal cross sections. The hatched bands indicate post-fit uncertainties (statistical and systematic) for the SM background predictions. |
png pdf |
Figure 5-a:
Distributions of the post-fit BDT discriminant targeting the CLFV top quark decay (left) and production (right) signal. Contributions from the two signal modes (production and decay) are combined within each SR and are shown as the solid red line. The post-fit signal strength ($ \mu_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}=\hat{\mu}_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}} $) is used to normalize the signal cross sections. The hatched bands indicate post-fit uncertainties (statistical and systematic) for the SM background predictions. |
png pdf |
Figure 5-b:
Distributions of the post-fit BDT discriminant targeting the CLFV top quark decay (left) and production (right) signal. Contributions from the two signal modes (production and decay) are combined within each SR and are shown as the solid red line. The post-fit signal strength ($ \mu_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}=\hat{\mu}_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}} $) is used to normalize the signal cross sections. The hatched bands indicate post-fit uncertainties (statistical and systematic) for the SM background predictions. |
png pdf |
Figure 6:
Two-dimensional 95% CL upper limits on the Wilson coefficients (left) and the branching fractions (right). The observed (expected) upper limits for tensor-, vector-, and scalar-like CLFV interactions are shown in red, blue, and black solid (dotted) lines, respectively. The shaded bands contain 68% of the distribution of the expected upper limits. |
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Figure 6-a:
Two-dimensional 95% CL upper limits on the Wilson coefficients (left) and the branching fractions (right). The observed (expected) upper limits for tensor-, vector-, and scalar-like CLFV interactions are shown in red, blue, and black solid (dotted) lines, respectively. The shaded bands contain 68% of the distribution of the expected upper limits. |
png pdf |
Figure 6-b:
Two-dimensional 95% CL upper limits on the Wilson coefficients (left) and the branching fractions (right). The observed (expected) upper limits for tensor-, vector-, and scalar-like CLFV interactions are shown in red, blue, and black solid (dotted) lines, respectively. The shaded bands contain 68% of the distribution of the expected upper limits. |
Tables | |
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Table 1:
Summary of relevant dimension-6 operators considered in this analysis. Here, $ \varepsilon $ is the two-dimensional Levi-Civita symbol, $ \gamma^\mu $ the Dirac gamma matrices, and $ \sigma^{\mu\nu}=\frac{i}{2}[\gamma^\mu,\gamma^\nu] $. The $ \mathrm{q} $ and $ \mathrm{l} $ denote left-handed doublets for leptons and quarks, respectively, whereas u and e denote right-handed singlets for quarks and leptons, respectively. The indices $ i $ and $ j $ are lepton flavor indices that run from 1 to 2 with $ i \neq j $; $ k $ and $ l $ are quark flavor indices with the condition that one of them is 3 and the other one is 1 or 2. The four vector-like operators are merged in this analysis because the final-state particles produced by these operators have very similar kinematics. |
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Table 2:
Theoretical cross sections for top quark production and decay for each CLFV coupling. The cross sections are calculated with $ C_{a}/\Lambda^2=$ 1 TeV$^{-2}$, $ m_{\mathrm{t}} = $ 172.5 GeV, $ \Gamma_{\mathrm{t}}^{\text{SM}} = $ 1.33 GeV. The cross section for the top quark decay process is the same for $ \mathrm{e}\mu\mathrm{t}\mathrm{u} $ and $ \mathrm{e}\mu\mathrm{t}\mathrm{c} $ couplings, therefore, only one cross section is quoted for each Lorentz structure. The first uncertainty represents the effect of QCD renormalization and factorization scales. The second uncertainty is the PDF uncertainty. |
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Table 3:
Summary of the selection criteria used to define different event regions. |
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Table 4:
Expected background contributions and the number of events observed in data collected during 2016-2018. The quoted uncertainties include statistical and systematic sources, which are added in quadrature. The category ``Other" includes smaller background contributions containing one or two top quarks plus a boson or quark. The CLFV signal, generated with $ C_{\mathrm{e}\mu\mathrm{t}\mathrm{u}}^{\text{vector}}/\Lambda^2=$ 1 TeV$^{-2}$, is also listed for reference and includes contributions from both top quark production and decay modes. |
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Table 5:
Summary of systematic uncertainties and the average change in signal and overall background yields in the SRs. Uncertainties that only contain normalization effects, such as luminosity uncertainties and uncertainties in theoretical cross sections, are not included in this table. |
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Table 6:
Upper limits at 95% CL on Wilson coefficients and the branching fractions for tensor-, vector-, and scalar-like CLFV interactions. The expected and observed upper limits are shown in regular and bold fonts, respectively. The intervals that contain 68% of the distribution of the expected upper limits are shown in parentheses. |
Summary |
This paper presents results from a search for charged-lepton flavor violation in both top quark production and decay processes. The data used were collected by the CMS experiment during 2016-2018 and correspond to an integrated luminosity of 138 fb$ ^{-1} $. Events were selected for analysis if they contain exactly three charged leptons--one electron and one muon of opposite electric charge as well as one additional electron or muon. Events must also contain at least one jet of which no more than one is associated with a bottom quark. An effective field theory approach is used for parametrizing the charged-lepton flavor violating interactions. Boosted decision trees are used to distinguish a possible signal from the background. No significant excess is observed over the prediction from the standard model. Upper limits at the 95% confidence level are set on the branching fractions involving up (charm) quarks, $ \mathrm{t}\to\mathrm{e}\mu\mathrm{u} $ ($ \mathrm{t}\to\mathrm{e}\mu\mathrm{c} $), of 0.032 (0.498) \times $10$^{-6} $, 0.022 (0.369) $\times $10$^{-6} $, and 0.012 (0.216) $\times $10$^{-6} $ for tensor, vector, and scalar interactions, respectively. These limits constitute the most stringent ones to date on these processes, improving the existing limits by roughly one order of magnitude. |
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