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| CMS-PAS-EXO-17-006 | ||
| Search for evidence of Type-III seesaw mechanism in multilepton final states in pp collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| March 2017 | ||
| Abstract: A search for a type-III seesaw signal in events with three or more electrons or muons is presented. The data sample corresponds to 35.9 fb$^{-1}$ of integrated luminosity in pp collisions at $\sqrt{s} = $ 13 TeV collected by the CMS experiment at the LHC in 2016. The signal is sought after in final states with at least three leptons, and has diverse kinematic properties. The primary selection is based on the number of leptons and the invariant mass of opposite-sign lepton pairs, and helps discriminate the signal against the standard model background. The final optimization for the type-III seesaw signal is based on the sum of leptonic transverse momenta and missing transverse energy, as well as the transverse mass. The observations are consistent with expectations from standard model processes. The results are used to exclude heavy fermions of the type-III seesaw model with masses below 850 GeV for the lepton-flavor democratic scenario. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRL 119 (2017) 221802. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
The $ {M_\textrm {T}} $ distribution in a WZ enriched selection of events with three leptons and one OSSF pair with mass on-Z, 50 $ < {E_{\mathrm {T}}^{\text {miss}}} < $ 100 GeV and $ {M_\textrm {T}} > $ 30 GeV (left), and the four-lepton invariant mass distribution in a ZZ enriched selection of events with four leptons and two OSSF pairs both of which are on-Z and $ {E_{\mathrm {T}}^{\text {miss}}} < $ 50 GeV (right). The total SM background is shown as a stack of all contributing processes, and the gray band in the lower panel represents the statistical uncertainty on the expected background. |
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Figure 1-a:
The $ {M_\textrm {T}} $ distribution in a WZ enriched selection of events with three leptons and one OSSF pair with mass on-Z, 50 $ < {E_{\mathrm {T}}^{\text {miss}}} < $ 100 GeV and $ {M_\textrm {T}} > $ 30 GeV. The total SM background is shown as a stack of all contributing processes, and the gray band in the lower panel represents the statistical uncertainty on the expected background. |
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Figure 1-b:
The four-lepton invariant mass distribution in a ZZ enriched selection of events with four leptons and two OSSF pairs both of which are on-Z and $ {E_{\mathrm {T}}^{\text {miss}}} < $ 50 GeV. The total SM background is shown as a stack of all contributing processes, and the gray band in the lower panel represents the statistical uncertainty on the expected background. |
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Figure 2:
The $ {M_\textrm {T}} $ distribution for events with three leptons and one OSSF pair, with mass on-Z and $ {E_{\mathrm {T}}^{\text {miss}}} > $ 100 GeV (top left), the $ {L_\textrm {T}} + {E_{\mathrm {T}}^{\text {miss}}} $ distribution for events with three leptons and one OSSF pair with mass above-Z (top right), the $ {L_\textrm {T}} + {E_{\mathrm {T}}^{\text {miss}}} $ distribution for events with three leptons and one OSSF pair, with mass below-Z and $ {E_{\mathrm {T}}^{\text {miss}}} > $ 50 GeV (bottom left) and with three leptons and no OSSF pairs (below right). The total SM background is shown as a stack of all contributing processes. The predictions for signal models with $m_{\varSigma } = $ 700 GeV (solid line) and $m_{\varSigma } = $ 380 GeV (dashed line) (sum of all production and decay modes) are also shown. The hatched gray band in the upper panel, and the dark and light gray bands in the lower panel represent the total, statistical, and systematic uncertainties on the expected background, respectively. |
png pdf |
Figure 2-a:
The $ {M_\textrm {T}} $ distribution for events with three leptons and one OSSF pair, with mass on-Z and $ {E_{\mathrm {T}}^{\text {miss}}} > $ 100 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for signal models with $m_{\varSigma } = $ 700 GeV (solid line) and $m_{\varSigma } = $ 380 GeV (dashed line) (sum of all production and decay modes) are also shown. The hatched gray band in the upper panel, and the dark and light gray bands in the lower panel represent the total, statistical, and systematic uncertainties on the expected background, respectively. |
png pdf |
Figure 2-b:
The $ {L_\textrm {T}} + {E_{\mathrm {T}}^{\text {miss}}} $ distribution for events with three leptons and one OSSF pair with mass above-Z. The total SM background is shown as a stack of all contributing processes. The predictions for signal models with $m_{\varSigma } = $ 700 GeV (solid line) and $m_{\varSigma } = $ 380 GeV (dashed line) (sum of all production and decay modes) are also shown. The hatched gray band in the upper panel, and the dark and light gray bands in the lower panel represent the total, statistical, and systematic uncertainties on the expected background, respectively. |
png pdf |
Figure 2-c:
The $ {L_\textrm {T}} + {E_{\mathrm {T}}^{\text {miss}}} $ distribution for events with three leptons and one OSSF pair, with mass below-Z and $ {E_{\mathrm {T}}^{\text {miss}}} > $ 50 GeV. The total SM background is shown as a stack of all contributing processes. The predictions for signal models with $m_{\varSigma } = $ 700 GeV (solid line) and $m_{\varSigma } = $ 380 GeV (dashed line) (sum of all production and decay modes) are also shown. The hatched gray band in the upper panel, and the dark and light gray bands in the lower panel represent the total, statistical, and systematic uncertainties on the expected background, respectively. |
png pdf |
Figure 2-d:
The $ {L_\textrm {T}} + {E_{\mathrm {T}}^{\text {miss}}} $ distribution for events with three leptons and no OSSF pairs. The total SM background is shown as a stack of all contributing processes. The predictions for signal models with $m_{\varSigma } = $ 700 GeV (solid line) and $m_{\varSigma } = $ 380 GeV (dashed line) (sum of all production and decay modes) are also shown. The hatched gray band in the upper panel, and the dark and light gray bands in the lower panel represent the total, statistical, and systematic uncertainties on the expected background, respectively. |
png pdf |
Figure 3:
The $ {L_\textrm {T}} + {E_{\mathrm {T}}^{\text {miss}}} $ distribution for events with four or more leptons and one OSSF pair (left), and with four or more leptons and at least two OSSF pairs (right). The total SM background is shown as a stack of all contributing processes. The predictions for signal models with $m_{\varSigma } = $ 700 GeV (solid line) and $m_{\varSigma } = $ 380 GeV (dashed line) (sum of all production and decay modes) are also shown. The hatched gray band in the upper panel, and the dark and light gray bands in the lower panel represent the total, statistical, and systematic uncertainties on the expected background, respectively. |
png pdf |
Figure 3-a:
The $ {L_\textrm {T}} + {E_{\mathrm {T}}^{\text {miss}}} $ distribution for events with four or more leptons and one OSSF pair. The total SM background is shown as a stack of all contributing processes. The predictions for signal models with $m_{\varSigma } = $ 700 GeV (solid line) and $m_{\varSigma } = $ 380 GeV (dashed line) (sum of all production and decay modes) are also shown. The hatched gray band in the upper panel, and the dark and light gray bands in the lower panel represent the total, statistical, and systematic uncertainties on the expected background, respectively. |
png pdf |
Figure 3-b:
The $ {L_\textrm {T}} + {E_{\mathrm {T}}^{\text {miss}}} $ distribution for events with four or more leptons and at least two OSSF pairs. The total SM background is shown as a stack of all contributing processes. The predictions for signal models with $m_{\varSigma } = $ 700 GeV (solid line) and $m_{\varSigma } = $ 380 GeV (dashed line) (sum of all production and decay modes) are also shown. The hatched gray band in the upper panel, and the dark and light gray bands in the lower panel represent the total, statistical, and systematic uncertainties on the expected background, respectively. |
png pdf |
Figure 4:
The 95% confidence level upper limits on the cross section sum for production of heavy fermion pairs ($ {\varSigma ^{0}} {\varSigma ^{+}}$, $ {\varSigma ^{0}} {\varSigma ^{-}}$, or $ {\varSigma ^{+}} {\varSigma ^{-}}$). In the flavor-democratic scenario, we rule out heavy fermion pair production for masses below 850 GeV (expected 790 GeV). |
| Tables | |
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Table 1:
The signal regions used in this search are summarized in terms of the number of leptons, the presence of an OSSF pair, and the kinematic variable used for discrimination. Each selection described here is further divided into eight bins in the kinematic variable, giving a total of 48 statistically independent signal regions. Additional criteria used to ensure that signal regions are non-overlapping with control regions are also stated. |
| Summary |
| In summary, we performed a search for type-III seesaw heavy fermions in multilepton final states using 35.9 fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = $ 13 TeV, collected using the CMS detector. We observe no significant discrepancies between the background prediction and the data. Assuming degenerate heavy fermion masses mS, we exclude previously unexplored regions of the signal model with heavy fermion particle with a mass limit for the lepton-flavor democratic scenario of 850 GeV at 95% confidence level. |
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