Search for top squarks and dark matter particles in opposite-charge dilepton final states at $\sqrt{s}=$ 13 TeV

The CMS collaboration
Phys.Rev. D97 (2018) 032009, 2018

Abstract (data abstract)
CERN-LHC. Search for top squarks and dark matter particles in opposite-charge dilepton final states at sqrt(s) = 13 TeV A search for new physics is presented in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from b quarks, and missing transverse momentum (pTmiss). The search uses proton-proton collision data at 13 TeV amounting to 35.9 $fb^{−1}$ of integrated luminosity collected using the CMS detector in 2016. Hypothetical signal events are efficiently separated from the dominant ttbar background with requirements on pTmiss and transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced top squarks. For top squarks, decaying exclusively to a top quark and a neutralino, exclusion limits are placed at 95% confidence level on the mass of the lightest top squark up to 800 GeV and on the lightest neutralino up to 360 GeV. These results, combined with searches in the single-lepton and all-jet final states, raise the exclusion limits up to 1050 GeV for the lightest top squark and up to 500 GeV for the lightest neutralino. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1300 GeV for top squarks and up to 800 GeV for the lightest neutralino. The results are also interpreted in a simplified model with a dark matter (DM) particle coupled to the top quark through a scalar or pseudoscalar mediator. For light DM, mediator masses up to 100 (50) GeV are excluded for scalar (pseudoscalar) mediators. The result for the scalar mediator achieves some of the most stringent limits to date in this model.

  • Figure 2a

    Data from Figure 2 (left) of publication

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    Figure 2 (left). Distribution of $M_{T2}(ll)$ in simulation after preselection and requiring $M_{T2}(ll) > 100$ GeV.

  • Figure 2b

    Data from Figure 2 (center) of publication

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    Figure 2 (center). Distribution of $M_{T2}(blbl)$ in simulation after preselection and requiring $M_{T2}(ll) > 100$ GeV.

  • Figure 2c

    Data from Figure 2 (right) of publication

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    Figure 2 (right). Distribution of $p_{T}^{miss}$ in simulation after preselection and requiring $M_{T2}(ll) > 100$ GeV.

  • Figure 3a

    Data from Figure 3 (upper) of publication

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    Figure 3 (upper). Distribution of $M_{T2}(ll)$ in a control region enriched in $t\bar{t}$ events defined by requiring at least 2...

  • Figure 4a

    Data from Figure 4 (upper) of publication

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    Figure 4 (upper). Expected and observed yields in the five $t\bar{t}Z$ control regions, which are defined by different requirements on...

  • Figure 4b

    Data from Figure 4 (lower) of publication

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    Figure 4 (lower). Expected and observed yields in the five $t\bar{t}Z$ control regions, which are defined by different requirements on...

  • Figure 5a

    Data from Figure 5 (left) of publication

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    Figure 5 (left). Distribution of $M_{T2}(ll)$ of SF events falling within in the Z boson mass window with at least...

  • Figure 5b

    Data from Figure 5 (center) of publication

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    Figure 5 (center). Distribution of $M_{T2}(blbl)$ of SF events falling within in the Z boson mass window with at least...

  • Figure 5c

    Data from Figure 5 (right) of publication

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    Figure 5 (right). Distribution of $p_{T}^{miss}$ of SF events falling within in the Z boson mass window with at least...

  • Figure 6

    Data from Figure 6 of publication

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    Figure 6. Event yields in the 13 Drell-Yan and multiboson control regions for events with SF leptons falling within the...

  • Figure 7a

    Data from Figure 7 (left) of publication

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    Figure 7 (left). Distributions of $M_{T2}(ll)$ for observed events in the dimuon channel compared to the predicted SM background.

  • Figure 7b

    Data from Figure 7 (center) of publication

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    Figure 7 (center). Distributions of $M_{T2}(ll)$ for observed events in the dielectron channel compared to the predicted SM background.

  • Figure 7c

    Data from Figure 7 (right) of publication

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    Figure 7 (right). Distributions of $M_{T2}(ll)$ for observed events in the electron-muon channel compared to the predicted SM background.

  • Figure 8a

    Data from Figure 8 (left) of publication

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    Figure 8 (left). Distributions of $M_{T2}(ll)$ for all lepton flavors for the defined selection.

  • Figure 8b

    Data from Figure 8 (center) of publication

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    Figure 8 (center). Distributions of $M_{T2}(blbl)$ for all lepton flavors for the defined selection, after requiring $M_{T2}(ll) > 100$ GeV.

  • Figure 8c

    Data from Figure 8 (right) of publication

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    Figure 8 (right). Distributions of $p_{T}^{miss}$ for all lepton flavors for the defined selection, after requiring $M_{T2}(ll) > 100$ GeV.

  • Figure 9a

    Data from Figure 9 (upper) of publication

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    Figure 9 (upper). Predicted backgrounds and observed yields in the dielectron and dimuon search regions. The yields are post fit...

  • Figure 9b

    Data from Figure 9 (lower) of publication

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    Figure 9 (lower). Predicted backgrounds and observed yields in the electron-muon search regions. The yields are post fit and correspond...

  • Figure 10

    Data from Figure 10 of publication

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    Figure 10. Predicted backgrounds and observed yields in all search regions combined. The yields are post fit and correspond to...

  • Figure 11a

    Data from Figure 11 (upper) of publication

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    Figure 11 (upper). Observed limits for the T2tt model in the top squark - LSP mass plane. The numbers indicate...

  • Figure 11a observed contour

    Data from Figure 11 (upper) of publication

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    Figure 11 (upper). Observed exclusion region at 95% CL assuming 100% branching fraction.

  • Figure 11a expected contour

    Data from Figure 11 (upper) of publication

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    Figure 11 (upper). Expected exclusion region at 95% CL assuming 100% branching fraction.

  • Figure 11b

    Data from Figure 11 (lower) of publication

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    Figure 11 (lower). Observed limits for the T2bW model in the top squark - LSP mass plane. The numbers indicate...

  • Figure 11b observed contour

    Data from Figure 11 (lower) of publication

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    Figure 11 (lower). Observed exclusion region at 95% CL assuming 100% branching fraction.

  • Figure 11b expected contour

    Data from Figure 11 (lower) of publication

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    Figure 11 (lower). Expected exclusion region at 95% CL assuming 100% branching fraction.

  • Figure 12a

    Data from Figure 12 (upper left) of publication

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    Figure 12 (upper left). Observed limits for the T8bbllnunu model in the top squark - LSP mass plane. The numbers...

  • Figure 12a observed contour

    Data from Figure 12 (upper left) of publication

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    Figure 12 (upper left). Observed exclusion region at 95% CL assuming 100% branching fraction. $m_{\tilde{\chi}^{\pm}_{1}} = 0.5 (m_{\tilde{t}_{1}} + m_{\tilde{\chi}^{0}_{1}})$,...

  • Figure 12a expected contour

    Data from Figure 12 (upper left) of publication

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    Figure 12 (upper left). Expected exclusion region at 95% CL assuming 100% branching fraction. $m_{\tilde{\chi}^{\pm}_{1}} = 0.5 (m_{\tilde{t}_{1}} + m_{\tilde{\chi}^{0}_{1}})$,...

  • Figure 12b

    Data from Figure 12 (upper right) of publication

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    Figure 12 (upper left). Observed limits for the T8bbllnunu model in the top squark - LSP mass plane. The numbers...

  • Figure 12b observed contour

    Data from Figure 12 (upper right) of publication

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    Figure 12 (upper left). Observed exclusion region at 95% CL assuming 100% branching fraction. $m_{\tilde{\chi}^{\pm}_{1}} = 0.5 (m_{\tilde{t}_{1}} + m_{\tilde{\chi}^{0}_{1}})$,...

  • Figure 12b expected contour

    Data from Figure 12 (upper right) of publication

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    Figure 12 (upper left). Expected exclusion region at 95% CL assuming 100% branching fraction. $m_{\tilde{\chi}^{\pm}_{1}} = 0.5 (m_{\tilde{t}_{1}} + m_{\tilde{\chi}^{0}_{1}})$,...

  • Figure 12c

    Data from Figure 12 (lower) of publication

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    Figure 12 (lower). Observed limits for the T8bbllnunu model in the top squark - LSP mass plane. The numbers indicate...

  • Figure 12c observed contour

    Data from Figure 12 (lower) of publication

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    Figure 12 (lower). Observed exclusion region at 95% CL assuming 100% branching fraction. $m_{\tilde{\chi}^{\pm}_{1}} = 0.5 (m_{\tilde{t}_{1}} + m_{\tilde{\chi}^{0}_{1}})$, $m_{\tilde{l}}...

  • Figure 12c expected contour

    Data from Figure 12 (lower) of publication

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    Figure 12 (lower). Expected exclusion region at 95% CL assuming 100% branching fraction. $m_{\tilde{\chi}^{\pm}_{1}} = 0.5 (m_{\tilde{t}_{1}} + m_{\tilde{\chi}^{0}_{1}})$, $m_{\tilde{l}}...

  • Figure 13

    Data from Figure 13 of publication

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    Figure 13. Observed limits for the T2tt model in the top squark - LSP mass plane combining the dilepton final...

  • Figure 13 observed contour

    Data from Figure 13 of publication

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    Figure 13. Observed exclusion region at 95% CL assuming 100% branching fraction.

  • Figure 13 expected contour

    Data from Figure 13 of publication

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    Figure 13. Expected exclusion region at 95% CL assuming 100% branching fraction.

  • Figure 14

    Data from Figure 14 of publication

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    Figure 14. Observed limits for the T2bW model in the top squark - LSP mass plane combining the dilepton final...

  • Figure 14 observed contour

    Data from Figure 14 of publication

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    Figure 14. Observed exclusion region at 95% CL assuming 100% branching fraction.

  • Figure 14 expected contour

    Data from Figure 14 of publication

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    Figure 14. Expected exclusion region at 95% CL assuming 100% branching fraction.

  • Additional Figure 3

    Data from additional Figure 3

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    Additional Figure 3. Observed limits for the T2tt model in the top squark - LSP mass plane using aggregate signal...

  • Additional Figure 3 observed contour

    Data from additional Figure 3

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    Additional Figure 3. Observed exclusion region at 95% CL assuming 100% branching fraction.

  • Additional Figure 3 expected contour

    Data from additional Figure 3

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    Additional Figure 3. Expected exclusion region at 95% CL assuming 100% branching fraction.

  • Table 5

    Data from Table 5 of publication

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    Table 5. Ratios of $\mu=\frac{\sigma$}{\sigma_{theory}}$ of the 95% CL expected and observed limits to simplified model expectations for different DM...

  • Table 6

    Data from Table 6 of publication

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    Table 6. Expected and observed event yields, summed over all lepton flavors, in aggregate signal regions.

  • Table 7a

    Data from Table 7 (upper) of publication

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    Table 7 (upper). Covariance matrix for the background prediction in aggregate signal regions.

  • Table 7b

    Data from Table 7 (lower) of publication

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    Table 7 (lower). Correlation matrix for the background prediction in aggregate signal regions.

  • Correlation

    Data from additional material Fig 1

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    Additional Figure 1. Correlation matrix of the 13 signal regions, split into same-flavor (SF) and different-flavor (DF) regions.

  • Covariance

    Data from additional material Fig 2

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    Additional Figure 2. Covariance matrix of the 13 signal regions, split into same-flavor (SF) and different-flavor (DF) regions.

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