We report a search for a heavy fourth-generation down-type quark
($b'$) which decays with 100\% branching ratio $b' \rightarrow tW$,
giving a significant number of same-charge dilepton events. In
addition, we search for exotic top partners $(B,T_{5/3})$ which have
similar decays. We select events with two same-charge leptons, missing
transverse energy, at least two jets and a positive $b$-tag.
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| Validation of Z in opposite sign-leptons |
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| Validation of top quark pairs in opposite-sign leptons, missing energy and a btag |
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| Dilepton invariant mass in same-charge dilepton events with two electrons |
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| Dilepton invariant mass in same-charge dilepton events with an electron and a muon |
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| Dilepton invariant mass in same-charge dilepton events with two muons |
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| Dilepton invariant mass in all same-charge dilepton events |
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| Missing transverse energy in same-charge dileptons |
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| Expected backgrounds in each channel |
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| Acceptance and expected yield for b' and B,T5/3 |
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| Yield, breakdown by channel |
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| Observed event yields by channel |
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| Best-fit signal cross-sections, relative to theoretical prediction |
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| Data, backgrounds and b' signal at the best-fit rate |
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| 95% C.L. upper limits on the cross-section as a function of mass, relative the theoretical predictions. |
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| Expected and observed limits compared to theoretical prediction for a b'. Also shown are 2 sigma deviations in the expectation. Note that due to the small number of events, approximiately half of simulated experiments yield a measured signal rate of zero; therefore both the median and -2 sigma deviations correspond to the same measured rate, of zero signal events.
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| Best-fit signal cross-sections, relative to theoretical prediction |
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| Data, backgrounds and B,T5/3 signal at the best-fit rate |
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| 95% C.L. upper limits on the cross-section as a function of mass, relative the theoretical predictions. |
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| Expected and observed limits compared to theoretical prediction for a B,T5/3. Also shown are 2 sigma deviations in the expectation. Note that due to the small number of events, approximately half of simulated experiments yield a measured signal rate of zero; therefore both the median and -2 sigma deviations correspond to the same measured rate, of zero signal events.
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| View of tracker for electron-muon 5-jet event |
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| LEGO view of calorimeter for electron-muon 5-jet event |
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| Selected objects in electron-muon 5-jet event |
| Object | Pt | Eta | Phi |
|---|
| Electron | 73.1 GeV | 0.99 | -1.02 |
| Muon | 20.6 GeV | 0.98 | -2.63 |
| Jet | 59.5 GeV | 1.27 | 2.71 |
| bJet | 42.3 GeV | 0.87 | -2.63 |
| Jet | 38.5 GeV | 1.36 | 0.44 |
| Jet | 33.4 GeV | 1.67 | 0.02 |
| Jet | 24.1 GeV | 0.80 | 1.96 |
| MET | 26.5 GeV | --- | 1.44 |
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| Invariant mass of object pairs in electron-muon 5-jet event |
| Object 1 | Object 2 | Mass(1,2) [GeV/c^2] |
|---|
| Electron | Muon | 55.9 |
| Jet 1 | Jet 2 | 49.9 |
| Jet 1 | Jet 3 | 83.1 |
| Jet 1 | Jet 4 | 79.2 |
| Jet 1 | Jet 5 | 47.9 |
| Jet 2 | Jet 3 | 86.9 |
| Jet 2 | Jet 4 | 88.7 |
| Jet 2 | Jet 5 | 33.0 |
| Jet 3 | Jet 4 | 18.7 |
| Jet 3 | Jet 5 | 45.4 |
| Jet 4 | Jet 5 | 53.3 |
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| View of tracker for muon-muon 3-jet event |
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| LEGO view of calorimeter for muon-muon 3-jet event |
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| Selected objets in muon-muon 3-jet event |
| Object | Pt | Eta | Phi |
|---|
| Muon | 79.7 GeV | 0.33 | -0.85 |
| Muon | 30.6 GeV | -0.57 | 2.85 |
| Jet | 77.5 GeV | -0.93 | 2.44 |
| Jet | 40.1 GeV | -0.66 | 2.92 |
| bJet | 25.2 GeV | -0.31 | 2.41 |
| MET | 86.6 GeV | --- | -0.21 |
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| Invariant mass of object pairs in muon-muon 3-jet event |
| Object 1 | Object 2 | Mass(1,2) [GeV/c^2] |
|---|
| Muon 1 | Muon 2 | 105.5 |
| Jet 1 | Jet 2 | 30.5 |
| Jet 1 | Jet 3 | 27.8 |
| Jet 2 | Jet 3 | 19.6 |
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