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| CMS-EXO-18-005 ; CERN-EP-2019-088 | ||
| Search for vector-like leptons in multilepton final states in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 27 May 2019 | ||
| Phys. Rev. D. 100 (2019) 052003 | ||
| Abstract: A search for vector-like leptons in multilepton final states is presented. The data sample corresponds to an integrated luminosity of 77.4 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016 and 2017. Events are categorized by the multiplicity of electrons, muons, and hadronically decaying $\tau$ leptons. The missing transverse momentum and the scalar sum of the lepton transverse momenta are used to distinguish the signal from background. The observed results are consistent with the expectations from the standard model hypothesis. The existence of a vector-like lepton doublet, coupling to the third generation standard model leptons in the mass range of 120-790 GeV, is excluded at 95% confidence level. These are the most stringent limits yet on the production of a vector-like lepton doublet, coupling to the third generation standard model leptons. | ||
| Links: e-print arXiv:1905.10853 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Two illustrative leading order Feynman diagrams for associated production of $\tau^{\prime}$ with a $\nu^{\prime} _{\tau}$ (left) and for pair production of $\tau^{\prime}$ (right), and possible subsequent decay chains that result in a multilepton final state. |
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Figure 1-a:
Illustrative leading order Feynman diagram for the associated production of $\tau^{\prime}$ with a $\nu^{\prime} _{\tau}$, and possible subsequent decay chains that result in a multilepton final state. |
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Figure 1-b:
Illustrative leading order Feynman diagram for the pair production of $\tau^{\prime}$, and possible subsequent decay chains that result in a multilepton final state. |
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Figure 2:
The upper row shows the ${m_{\mathrm {T}}}$ (left) and the ${L_\mathrm {T}}$ (right) distributions in the WZ control region in data and simulation. The WZ control region contains events with three leptons and an OSSF pair with mass on-Z, and 50 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 100 GeV. The lower row shows the $m_{4\ell}$ (left) and the ${L_\mathrm {T}}$ (right) distributions in the ZZ control region. The ZZ control region contains events with two OSSF lepton pairs, both of which are on-Z, and $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events. |
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Figure 2-a:
${L_\mathrm {T}}$ distribution in the WZ control region in data and simulation. The WZ control region contains events with three leptons and an OSSF pair with mass on-Z, and 50 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 100 GeV. The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 2-b:
The upper row shows the ${m_{\mathrm {T}}}$ (left) and the ${L_\mathrm {T}}$ (right) distributions in the WZ control region in data and simulation. The WZ control region contains events with three leptons and an OSSF pair with mass on-Z, and 50 $ < {{p_{\mathrm {T}}} ^\text {miss}} < $ 100 GeV. The lower row shows the $m_{4\ell}$ (left) and the ${L_\mathrm {T}}$ (right) distributions in the ZZ control region. The ZZ control region contains events with two OSSF lepton pairs, both of which are on-Z, and $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events. |
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Figure 2-c:
$m_{4\ell}$ distribution in the ZZ control region. The ZZ control region contains events with two OSSF lepton pairs, both of which are on-Z, and $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 2-d:
${L_\mathrm {T}}$ distribution in the ZZ control region. The ZZ control region contains events with two OSSF lepton pairs, both of which are on-Z, and $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 3:
The dilepton mass (left) and the ${L_\mathrm {T}}$ (right) distributions in data and simulation in a misidentified ${\tau _\mathrm {h}}$ control region. This control region contains 2L1T (OS) events with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events. |
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Figure 3-a:
The dilepton mass distribution in data and simulation in a misidentified ${\tau _\mathrm {h}}$ control region. This control region contains 2L1T (OS) events with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 3-b:
${L_\mathrm {T}}$ distribution in data and simulation in a misidentified ${\tau _\mathrm {h}}$ control region. This control region contains 2L1T (OS) events with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 4:
The ${L_\mathrm {T}}$ distributions for the 3L signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 150 GeV (upper left) and $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 150 GeV (upper right), and for the 4L signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV (lower left) and $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 50 GeV (lower right). The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (the sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are shown as dashed lines. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events. |
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Figure 4-a:
The ${L_\mathrm {T}}$ distribution for the 3L signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 150 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (the sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are shown as dashed lines. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 4-b:
The ${L_\mathrm {T}}$ distribution for the 3L signal regions with ${{p_{\mathrm {T}}} ^\text {miss}} > $ 150 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (the sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are shown as dashed lines. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 4-c:
The ${L_\mathrm {T}}$ distribution for the 4L signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (the sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are shown as dashed lines. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 4-d:
The ${L_\mathrm {T}}$ distribution for the 4L signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (the sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are shown as dashed lines. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 5:
The ${L_\mathrm {T}}$ distributions for the 2L1T OS signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 150 GeV (upper left) and $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 150 GeV (upper right), and for the 2L1T SS signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 150 GeV (lower left) and $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 150 GeV (lower right). The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are also shown as dashed lines. The hatched gray bands in the upper panels represent the total uncertainty in the expected background. The lower panels show the ratios of observed data to the total expected background. In the lower panels, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bins include the overflow events. |
png pdf |
Figure 5-a:
The ${L_\mathrm {T}}$ distribution for the 2L1T OS signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 150 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are also shown as dashed lines. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
png pdf |
Figure 5-b:
The ${L_\mathrm {T}}$ distribution for the 2L1T OS signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 150 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are also shown as dashed lines. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
png pdf |
Figure 5-c:
The ${L_\mathrm {T}}$ distribution for the 2L1T SS signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} < $ 150 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are also shown as dashed lines. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
png pdf |
Figure 5-d:
The ${L_\mathrm {T}}$ distribution for the 2L1T SS signal regions with $ {{p_{\mathrm {T}}} ^\text {miss}} > $ 150 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for VLL signal models (sum of all production and decay modes) with $m_{\tau^{\prime}/\nu^{\prime}} = $ 200 and 500 GeV are also shown as dashed lines. The hatched gray bands in the upper panel represent the total uncertainty in the expected background. The lower panel shows the ratios of observed data to the total expected background. In the lower panel, the light gray band represents the combined statistical and systematic uncertainty in the expected background, while the dark gray band represents the statistical uncertainty only. The rightmost bin includes the overflow events. |
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Figure 6:
The 95$%$ confidence level upper limits on the total cross section for associated ($\tau^{\prime \pm} \nu^{\prime} _{\tau}$) and pair ($\tau^{\prime +} \tau^{\prime -}$/$\nu^{\prime} _{\tau}\nu^{\prime} _{\tau}$) production of VLLs. Also shown is the theoretical prediction for the production cross section of a vector-like lepton doublet coupling to the third generation SM leptons. The observed (expected) exclusion limit on the masses of VLLs is in the range of 120-790 (120-680) GeV. |
| Tables | |
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Table 1:
The signal regions defined in this analysis. The on-Z mass window is defined as 76 $ < m_{\ell \ell} < $ 106 GeV, while the below-Z condition is defined as $m_{\ell \ell} < $ 76 GeV. |
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Table 2:
The sources of systematic uncertainty and the typical variations (%) observed in the affected background and signal yields in the analysis. All sources of uncertainty are considered as correlated between the 2016 and 2017 data analyses except for the lepton identification and isolation, the single lepton trigger, and the integrated luminosity. The label ALL is defined as WZ, ZZ, Rare (${\mathrm{t} {}\mathrm{\bar{t}}} $V, VVV, Higgs boson), and Signal processes. |
| Summary |
| A search for vector-like leptons coupled to the third generation standard model leptons has been performed in several multilepton final states using 77.4 fb$^{-1}$ of proton-proton collision data at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2016 and 2017. No significant deviations of the data from the standard model predictions are observed. These results exclude a vector-like lepton doublet with a common mass in the range 120-790 GeV at 95% confidence level. These are the most stringent limits yet on the production of a vector-like lepton doublet, coupling to the third generation standard model leptons. |
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