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CMS-PAS-FTR-22-002
Search for a vector-like quark T decaying to bW, tZ, tH in the single lepton final state at the HL-LHC
Abstract: A simulation-based projection study is presented for a search for a vector-like top quark partner T in proton-proton (pp) collisions at $ {\sqrt{\text{s}}} = $ 14 TeV. The search considers the operational conditions of the High-Luminosity LHC (HL-LHC). The production $ {\text{pp} \rightarrow \text{T}\bar{\text{T}}} $ is followed by the decays $ {\text{T} \rightarrow \text{bW}} $, $ {\text{T} \rightarrow \text{tH}} $, and $ {\text{T} \rightarrow \text{tZ}} $ with equal branching fractions of 1/3. Events with one electron or muon, missing transverse momentum and jets are considered. For an integrated luminosity of 3000 fb$ ^{-1} $, the search projects to exclude a T mass below 1750 GeV at the 95% confidence level assuming equal branching fractions for $ {\text{T}\rightarrow \text{bW}/\text{tH}/\text{tZ}} $. Conversely, a T quark with mass up to 1440 GeV can be discovered at the HL-LHC with a significance of five standard deviations.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Leading-order Feynman diagrams showing $ \mathrm{T}\overline{\mathrm{T}} $ production along with the subsequent decays $ \mathrm{T}\rightarrow \mathrm{b}\mathrm{W} $ (left), $ \mathrm{T}\rightarrow \mathrm{t}\mathrm{Z} $ (middle) and $ \mathrm{T}\rightarrow \mathrm{t}\mathrm{H} $ (right).

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Figure 1-a:
Leading-order Feynman diagrams showing $ \mathrm{T}\overline{\mathrm{T}} $ production along with the subsequent decay $ \mathrm{T}\rightarrow \mathrm{b}\mathrm{W} $.

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Figure 1-b:
Leading-order Feynman diagrams showing $ \mathrm{T}\overline{\mathrm{T}} $ production along with the subsequent decay $ \mathrm{T}\rightarrow \mathrm{t}\mathrm{Z} $.

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Figure 1-c:
Leading-order Feynman diagrams showing $ \mathrm{T}\overline{\mathrm{T}} $ production along with the subsequent decay $ \mathrm{T}\rightarrow \mathrm{t}\mathrm{H} $.

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Figure 2:
Number of AK4 jets (left) and b-tagged AK4 jets (right) for signal and background processes. The signal distributions are scaled by factors of 20, 2000 and 200'000, depending on the T mass.

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Figure 2-a:
Number of AK4 jets for signal and background processes. The signal distributions are scaled by factors of 20, 2000 and 200'000, depending on the T mass.

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Figure 2-b:
Number of b-tagged AK4 jets for signal and background processes. The signal distributions are scaled by factors of 20, 2000 and 200'000, depending on the T mass.

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Figure 3:
Multiplicity for the W-tagged (top), single b-tagged H (bottom left) and doubly b-tagged H AK8 jets (bottom right). The signal distributions are scaled by factors of 20, 2000 and 200'000, depending on the T mass.

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Figure 3-a:
Multiplicity for the W-tagged AK8 jets. The signal distributions are scaled by factors of 20, 2000 and 200'000, depending on the T mass.

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Figure 3-b:
Multiplicity for the single b-tagged H AK8 jets. The signal distributions are scaled by factors of 20, 2000 and 200'000, depending on the T mass.

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Figure 3-c:
Multiplicity for the doubly b-tagged H AK8 jets. The signal distributions are scaled by factors of 20, 2000 and 200'000, depending on the T mass.

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Figure 4:
Distributions in $ S_{\text{T}} $ for signal and background processes. The signal distributions are scaled by factors of 20, 2000 and 200\,000, depending on the T mass.

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Figure 5:
Expected upper limits at 95% CL on the $ \mathrm{T}\overline{\mathrm{T}} $ production cross section. The inner (green) and the outer (yellow) bands indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis.

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Figure 6:
Projected exclusion limits at 95% CL on the T mass (left) and the expected discovery significances (right), as a function of integrated luminosity at the HL-LHC, assuming equal branching fractions for $ {\mathrm{T}\rightarrow \mathrm{b}\mathrm{W}} $, $ {\mathrm{T}\rightarrow \mathrm{t}\mathrm{H}} $, and $ {\mathrm{T}\rightarrow \mathrm{t}\mathrm{Z}} $ decays.

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Figure 6-a:
Projected exclusion limits at 95% CL on the T mass, as a function of integrated luminosity at the HL-LHC, assuming equal branching fractions for $ {\mathrm{T}\rightarrow \mathrm{b}\mathrm{W}} $, $ {\mathrm{T}\rightarrow \mathrm{t}\mathrm{H}} $, and $ {\mathrm{T}\rightarrow \mathrm{t}\mathrm{Z}} $ decays.

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Figure 6-b:
Expected discovery significances, as a function of integrated luminosity at the HL-LHC, assuming equal branching fractions for $ {\mathrm{T}\rightarrow \mathrm{b}\mathrm{W}} $, $ {\mathrm{T}\rightarrow \mathrm{t}\mathrm{H}} $, and $ {\mathrm{T}\rightarrow \mathrm{t}\mathrm{Z}} $ decays.

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Figure 7:
Discovery potential of a fermionic top partner T as a function of T mass versus integrated luminosity. The blue dashed and red solid lines represent discoveries at expected significances of three and five standard deviations, respectively.
Tables

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Table 1:
Definition of eight exclusive SRs on the basis of number of H-tagged, W-tagged, and b-tagged jets in the event.

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Table 2:
Summary of the systematic uncertainties used in this analysis and their effect on signal cross-section.
Summary
This study presented the expected sensitivity of the CMS experiment to a $ \mathrm{T}\overline{\mathrm{T}} $ production in single lepton final states, considering the subsequent decays $ \mathrm{T}\rightarrow \mathrm{b}\mathrm{W} $, $ \mathrm{T}\rightarrow \mathrm{t}\mathrm{H} $, and $ \mathrm{T}\rightarrow \mathrm{t}\mathrm{Z} $, with a dataset of 3000 fb$ ^{-1} $ of 14 TeV proton proton collisions, expected to be collected at the LHC. The signal and background samples have been simulated with DELPHES 3 considering the CMS Phase-2 detector geometry. At 95% CL, the study projects to exclude a T mass up to 1750 GeV, which is significantly higher than the existing Run 2 results. With 3000 fb$ ^{-1} $, this study shows the prospect for a T discovery up to masses of 1440 GeV.
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Compact Muon Solenoid
LHC, CERN