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| CMS-B2G-16-024 ; CERN-EP-2017-107 | ||
| Search for pair production of vector-like T and B quarks in single-lepton final states using boosted jet substructure techniques at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 12 June 2017 | ||
| JHEP 11 (2017) 085 | ||
| Abstract: A search for pair production of massive vector-like T and B quarks in proton-proton collisions at $\sqrt{s} = $ 13 TeV is presented. The data set was collected in 2015 by the CMS experiment at the LHC and corresponds to an integrated luminosity of up to 2.6 fb$^{-1}$. The T and B quarks are assumed to decay through three possible channels into a heavy boson (either a W, Z or Higgs boson) and a third generation quark. This search is performed in final states with one charged lepton and several jets, exploiting techniques to identify W or Higgs bosons decaying hadronically with large transverse momenta. No excess over the predicted standard model background is observed. Upper limits at 95% confidence level on the T quark pair production cross section are set that exclude T quark masses below 860 GeV in the singlet, and below 830 GeV in the doublet branching fraction scenario. For other branching fraction combinations with $\mathcal{B}(\mathrm{ t }\mathrm{ H }) + \mathcal{B}(\mathrm{ b }\mathrm{ W }) \geq $ 0.4, lower limits on the T quark range from 790 to 940 GeV. Limits are also set on pair production of singlet vector-like B quarks, which can be excluded up to a mass of 730 GeV. These limits are among the most stringent to date for vector-like T quarks. The techniques showcased here for understanding highly-boosted final states are important as the sensitivity to new particles is extended to higher masses. | ||
| Links: e-print arXiv:1706.03408 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Examples of leading-order Feynman diagrams showing production of a $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ pair with the T quark decaying to bW (left), tH (middle), and tZ (right). |
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Figure 1-a:
Example of leading-order Feynman diagram showing production of a $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ pair with the T quark decaying to bW. |
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Figure 1-b:
Example of leading-order Feynman diagram showing production of a $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ pair with the T quark decaying to tH. |
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Figure 1-c:
Example of leading-order Feynman diagram showing production of a $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ pair with the T quark decaying to tZ. |
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Figure 2:
Angular separations $\Delta {R}$ between the products of simulated $\mathrm{ W } \to \mathrm{ q } \mathrm{ \bar{q} } '$ (left) and $\mathrm{ H } \to {\mathrm{ b \bar{b} } } $ (right) decay processes for three different mass points of the T quark. Even for the lowest mass point shown, the final state particles are very often emitted with a separation of $\Delta {R} < $ 0.8 and are merged into an AK8 jet. |
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Figure 2-a:
Angular separations $\Delta {R}$ between the products of the simulated $\mathrm{ W } \to \mathrm{ q } \mathrm{ \bar{q} } '$ decay process for three different mass points of the T quark. Even for the lowest mass point shown, the final state particles are very often emitted with a separation of $\Delta {R} < $ 0.8 and are merged into an AK8 jet. |
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Figure 2-b:
Angular separations $\Delta {R}$ between the products of the simulated $\mathrm{ H } \to {\mathrm{ b \bar{b} } } $ decay process for three different mass points of the T quark. Even for the lowest mass point shown, the final state particles are very often emitted with a separation of $\Delta {R} < $ 0.8 and are merged into an AK8 jet. |
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Figure 3:
Distributions of the number of b-tagged subjets of the highest $ {p_{\mathrm {T}}} $ H-tagged jet candidate with $ {p_{\mathrm {T}}} > $ 300 GeV and $M_\text {jet}$ in the range [60, 160] GeV (left), and $M_\text {jet}$ of the highest $ {p_{\mathrm {T}}} $ H-tagged jet candidate with $ {p_{\mathrm {T}}} > $ 300 GeV and two subjet b tags (right). A T quark signal with $ M(\mathrm{T}) = $ 0.8 TeV is shown (right), normalized to the predicted cross section and scaled by a factor of 20, with the singlet benchmark branching fractions assumed. The solid (dashed) curve shows $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ events with at least one (zero) Higgs boson decay, where contributions from each decay mode are weighted to reflect the singlet branching fraction scenario. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 3-a:
Distribution of the number of b-tagged subjets of the highest $ {p_{\mathrm {T}}} $ H-tagged jet candidate with $ {p_{\mathrm {T}}} > $ 300 GeV and $M_\text {jet}$ in the range [60, 160] GeV. The solid (dashed) curve shows $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ events with at least one (zero) Higgs boson decay, where contributions from each decay mode are weighted to reflect the singlet branching fraction scenario. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 3-b:
Distribution of $M_\text {jet}$ of the highest $ {p_{\mathrm {T}}} $ H-tagged jet candidate with $ {p_{\mathrm {T}}} > $ 300 GeV and two subjet b tags. A T quark signal with $ M(\mathrm{T}) = $ 0.8 TeV is shown, normalized to the predicted cross section and scaled by a factor of 20, with the singlet benchmark branching fractions assumed. The solid (dashed) curve shows $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ events with at least one (zero) Higgs boson decay, where contributions from each decay mode are weighted to reflect the singlet branching fraction scenario. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 4:
Distributions of $ {S_\mathrm {T}} $ in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ (left) and W + jets (right) control regions of the boosted H channel after applying all corrections to their shape and normalization. The $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal, shown for T quark masses of 0.8 and 1.2 TeV, is normalized to the theoretical cross section and the singlet benchmark branching fractions are assumed. The uncertainty in the background includes statistical and systematic uncertainties described in Section 7. |
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Figure 4-a:
Distribution of $ {S_\mathrm {T}} $ in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ control region of the boosted H channel after applying all corrections to their shape and normalization. The $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal, shown for T quark masses of 0.8 and 1.2 TeV, is normalized to the theoretical cross section and the singlet benchmark branching fractions are assumed. The uncertainty in the background includes statistical and systematic uncertainties described in Section 7. |
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Figure 4-b:
Distribution of $ {S_\mathrm {T}} $ in the W + jets control region of the boosted H channel after applying all corrections to their shape and normalization. The $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal, shown for T quark masses of 0.8 and 1.2 TeV, is normalized to the theoretical cross section and the singlet benchmark branching fractions are assumed. The uncertainty in the background includes statistical and systematic uncertainties described in Section 7. |
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Figure 5:
Distribution of $\Delta R(\ell,j_2)$ in the boosted W channel after all selection requirements except for $\Delta R(\ell,j_2)> $ 1. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 6:
Distributions of (left-to-right, upper-to-lower) pruned jet quark mass for AK8 jets passing $\tau _2/\tau _1 < $ 0.6, $\tau _2/\tau _1$ for AK8 jets with pruned mass within 65-105 GeV, number of b-tagged AK4 jets, and number of W-tagged AK8 jets in the boosted W channel with all categories combined. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively, in the upper figures. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 6-a:
Distribution of the pruned jet quark mass for AK8 jets passing $\tau _2/\tau _1 < $ 0.6, in the boosted W channel with all categories combined. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively, in the upper figures. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 6-b:
Distribution of $\tau _2/\tau _1$ for AK8 jets with pruned mass within 65-105 GeV, in the boosted W channel with all categories combined. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively, in the upper figures. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 6-c:
Distribution of the number of b-tagged AK4 jets, in the boosted W channel with all categories combined. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively, in the upper figures. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 6-d:
Distribution of the number of W-tagged AK8 jets, in the boosted W channel with all categories combined. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively, in the upper figures. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 7:
Distributions of $\mathrm{min} [M(\ell, j)]$ in events without b-tagged AK4 jets (left) and $\mathrm{min} [M(\ell, \mathrm{ b })]$ in events with ${\geq }$1 b-tagged AK4 jets (right) in the boosted W channel with all categories combined. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 7-a:
Distribution of $\mathrm{min} [M(\ell, j)]$ in events without b-tagged AK4 jets in the boosted W channel with all categories combined. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 7-b:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in events with ${\geq }$1 b-tagged AK4 jets in the boosted W channel with all categories combined. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV, scaled by factors of 20 and 60, respectively. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 8:
Distributions of $\mathrm{min} [M(\ell, j)]$ in the W + jets control region of the boosted W channel (upper) for 0/${\geq }$1 W tag categories (left/right), and $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ control region of the boosted W channel (lower) for 1/${\geq }$2 b tag categories (left/right). Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 8-a:
Distribution of $\mathrm{min} [M(\ell, j)]$ in the W + jets control region of the boosted W channel for the 0 W tag category. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 8-b:
Distribution of $\mathrm{min} [M(\ell, j)]$ in the W + jets control region of the boosted W channel for the ${\geq }$1 W tag category. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 8-c:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ control region of the boosted W channel for the 1 b tag category. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 8-d:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ control region of the boosted W channel for the ${\geq }$2 b tag category. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9:
Distributions of $\mathrm{min} [M(\ell, j)]$ or $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the combination of electron and muon channels in the boosted W categories with 0 (left) or ${\geq }$1 (right) W-tagged jets and (upper to lower) 0, 1, 2, or ${\geq }$3 b-tagged jets. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9-a:
Distribution of $\mathrm{min} [M(\ell, j)]$ in the combination of electron and muon channels in the boosted W categories with 0 W-tagged jet and 0 b-tagged jet. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9-b:
Distribution of $\mathrm{min} [M(\ell, j)]$ in the combination of electron and muon channels in the boosted W categories with ${\geq }$1 W-tagged jets and 0 b-tagged jet. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9-c:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the combination of electron and muon channels in the boosted W categories with 0 W-tagged jet and 1 b-tagged jets. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9-d:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the combination of electron and muon channels in the boosted W categories with ${\geq }$1 W-tagged jets and 1 b-tagged jets. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9-e:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the combination of electron and muon channels in the boosted W categories with 0 W-tagged jet and 2 b-tagged jets. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9-f:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the combination of electron and muon channels in the boosted W categories with ${\geq }$1 W-tagged jets and 2 b-tagged jets. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9-g:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the combination of electron and muon channels in the boosted W categories with 0 W-tagged jet and ${\geq }$3 b-tagged jets. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 9-h:
Distribution of $\mathrm{min} [M(\ell, \mathrm{ b })]$ in the combination of electron and muon channels in the boosted W categories with ${\geq }$1 W-tagged jets and ${\geq }$3 b-tagged jets. Also shown are the distributions of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal events with T quark masses of 0.8 and 1.2 TeV. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 10:
Distributions of $ {S_\mathrm {T}} $ in the H1b (left) and H2b (right) categories in the combination of electron and muon channels. The $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal, shown for T quark masses of 0.8 and 1.2 TeV, is normalized to the theoretical cross section and the singlet benchmark branching fractions are assumed. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 10-a:
Distribution of $ {S_\mathrm {T}} $ in the H1b category in the combination of electron and muon channels. The $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal, shown for T quark masses of 0.8 and 1.2 TeV, is normalized to the theoretical cross section and the singlet benchmark branching fractions are assumed. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 10-b:
Distribution of $ {S_\mathrm {T}} $ in the H2b category in the combination of electron and muon channels. The $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal, shown for T quark masses of 0.8 and 1.2 TeV, is normalized to the theoretical cross section and the singlet benchmark branching fractions are assumed. The uncertainty in the background includes the statistical and systematic uncertainties described in Section 7. |
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Figure 11:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production for 100% $ {\mathrm {T}} \to \mathrm{ b } \mathrm{ W } $ in the boosted W channel (left), and 100% T $\to $ tH in the boosted H channel (right). The theoretically predicted cross section for $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 11-a:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production for 100% $ {\mathrm {T}} \to \mathrm{ b } \mathrm{ W } $ in the boosted W channel. The theoretically predicted cross section for $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 11-b:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production for 100% T $\to $ tH in the boosted H channel. The theoretically predicted cross section for $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 12:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production for the singlet benchmark (left) and the doublet benchmark (right) after combining the boosted W and boosted H channels. The theoretically predicted cross section for $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 12-a:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production for the singlet benchmark after combining the boosted W and boosted H channels. The theoretically predicted cross section for $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 12-b:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production for the doublet benchmark after combining the boosted W and boosted H channels. The theoretically predicted cross section for $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 13:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {B}} {\overline {\mathrm {B}}} } $ production for the singlet benchmark (left) and the doublet benchmark (right) after combining the boosted W and boosted H channels. The theoretically predicted cross section for $ { {\mathrm {B}} {\overline {\mathrm {B}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 13-a:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {B}} {\overline {\mathrm {B}}} } $ production for the singlet benchmark after combining the boosted W and boosted H channels. The theoretically predicted cross section for $ { {\mathrm {B}} {\overline {\mathrm {B}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 13-b:
The expected and observed upper limits (Bayesian) at 95% CL on the cross section of $ { {\mathrm {B}} {\overline {\mathrm {B}}} } $ production for the doublet benchmark after combining the boosted W and boosted H channels. The theoretically predicted cross section for $ { {\mathrm {B}} {\overline {\mathrm {B}}} } $ production calculated at NNLO is shown as red line, with the uncertainties in the PDFs and renormalization and factorization scales indicated by the shaded area. |
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Figure 14:
The expected (left) and observed (right) at 95% CL lower limits (Bayesian) on the T quark mass for a variety of $ {\mathrm {T}} \to \mathrm{ t } \mathrm{ H } $ and $ {\mathrm {T}} \to \mathrm{ b } \mathrm{ W } $ branching fraction combinations, indicated by the coordinates at the center of each box, after combining the boosted W and boosted H channels. A limit of $<$ 700 GeV indicates that this search is not sensitive to T quark decays with that branching fraction combination. |
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Figure 14-a:
The expected at 95% CL lower limit (Bayesian) on the T quark mass for a variety of $ {\mathrm {T}} \to \mathrm{ t } \mathrm{ H } $ and $ {\mathrm {T}} \to \mathrm{ b } \mathrm{ W } $ branching fraction combinations, indicated by the coordinates at the center of each box, after combining the boosted W and boosted H channels. A limit of $<$ 700 GeV indicates that this search is not sensitive to T quark decays with that branching fraction combination. |
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Figure 14-b:
The observed at 95% CL lower limit (Bayesian) on the T quark mass for a variety of $ {\mathrm {T}} \to \mathrm{ t } \mathrm{ H } $ and $ {\mathrm {T}} \to \mathrm{ b } \mathrm{ W } $ branching fraction combinations, indicated by the coordinates at the center of each box, after combining the boosted W and boosted H channels. A limit of $<$ 700 GeV indicates that this search is not sensitive to T quark decays with that branching fraction combination. |
| Tables | |
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Table 1:
Predicted cross sections for pair production of T or B quarks for various masses. Uncertainties include contributions from energy scale variations and from the PDFs. |
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Table 2:
Summary of the systematic uncertainties. The second column gives the magnitude of normalization uncertainties or the procedure used to evaluate shape uncertainties. The symbols (W), (H) indicate values for the boosted W or boosted H channels, and $\sigma $ indicates one standard deviation of the corresponding systematic uncertainty. Renormalization and factorization energy scale uncertainties are treated as shape-only for signal but include normalization uncertainties in background. Values stated for shape uncertainties indicate a representative range over the categories for the dominant backgrounds and/or signal. |
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Table 3:
Signal efficiencies in the boosted W and boosted H event categories, split into the six possible final states, of both $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ and $ { {\mathrm {B}} {\overline {\mathrm {B}}} } $ production for two illustrative mass points. Efficiencies are calculated with respect to the expected number of events in the corresponding final state before any selection. The relative uncertainty in the efficiencies after combining systematic and statistical uncertainties in the MC samples is about 8% in the boosted W categories and about 12% in the boosted H categories. |
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Table 4:
Number of events in each category after combining the electron and muon channels. Uncertainties include statistical and all systematic components (Table 2). Yields of $ { {\mathrm {T}} {\overline {\mathrm {T}}} } $ signal assume the theoretically predicted production cross section within the singlet branching fraction scenario. |
| Summary |
| The first search by CMS for pair-produced vector-like T and B quarks at $\sqrt{s}= $ 13 TeV is presented, using data from proton-proton collisions recorded in 2015 corresponding to integrated luminosities of 2.3-2.6 fb$^{-1}$. The search requires at least one lepton in the final state and is optimized for cases where a T quark decays to a boosted W or Higgs boson. No excess above the standard model background is observed and 95% confidence level upper limits are placed on the cross section of $ \mathrm{ t \bar{t} } $ and $ \mathrm{ b \bar{b} } $ production. For an electroweak singlet T quark, masses below 860 GeV are excluded, and for a doublet T quark, masses below 830 GeV are excluded. Considering other possible branching fraction combinations for T quarks, and assuming that the sum of the branching fractions to bW, tH and tZ is equal to unity, we set lower mass limits that range from 790 to 940 GeV for combinations with $\mathcal{B}(\mathrm{ t }\mathrm{ H }) + \mathcal{B}(\mathrm{ b }\mathrm{ W }) \geq $ 0.4. These results represent the most stringent limits to date for many possible T quark decay scenarios, and showcase the importance of new techniques for understanding highly-boosted final states in extending searches for new particles to higher masses. |
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