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| CMS-B2G-15-008 ; CERN-EP-2016-279 | ||
| Search for single production of a heavy vector-like T quark decaying to a Higgs boson and a top quark with a lepton and jets in the final state | ||
| CMS Collaboration | ||
| 3 December 2016 | ||
| Phys. Lett. B 771 (2017) 80 | ||
| Abstract: A search for single production of vector-like top quark partners (T) decaying into a Higgs boson and a top quark is performed using data from pp collisions at a centre-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 2.3 fb$^{-1}$. The top quark decay includes an electron or a muon while the Higgs boson decays into a pair of b quarks. No significant excess over standard model backgrounds is observed. Exclusion limits on the product of the production cross section and the branching fraction are derived in the T quark mass range 700 to 1800 GeV. For a mass of 1000 GeV, values of the product of the production cross section and the branching fraction greater than 0.8 and 0.7 pb are excluded at 95% confidence level, assuming left- and right-handed coupling of the T quark to standard model particles, respectively. This is the first analysis setting exclusion limits on the cross section of singly produced vector-like T quarks at a centre-of-mass energy of 13 TeV. | ||
| Links: e-print arXiv:1612.00999 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Production and decay mechanisms of a vector-like T quark, as targeted in this analysis. |
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Figure 2:
Distributions of kinematic variables after baseline selection. Electron and muon $ {p_{\mathrm {T}}} $ distributions are depicted in the upper-left and upper-right panels. The lower-left panel shows $S_\mathrm {T}$ in the electron channel while the soft-drop mass of the Higgs boson candidate in the muon channel is depicted in the lower right. The different background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. Signal cross sections are enhanced by a factor of 20. |
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Figure 2-a:
Distribution of the electron $ {p_{\mathrm {T}}} $ after baseline selection. The background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. Signal cross sections are enhanced by a factor of 20. |
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Figure 2-b:
Distribution of the muon $ {p_{\mathrm {T}}} $ after baseline selection. The background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. Signal cross sections are enhanced by a factor of 20. |
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Figure 2-c:
Distribution of $S_\mathrm {T}$ in the electron channel after baseline selection. The background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. Signal cross sections are enhanced by a factor of 20. |
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Figure 2-d:
Distribution of the soft-drop mass of the Higgs boson candidate in the muon channel after baseline selection. The background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. Signal cross sections are enhanced by a factor of 20. |
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Figure 3:
Mass (left) and $ {p_{\mathrm {T}}} $ (right) distributions of the reconstructed top quark candidate in the muon channel after the baseline selection. The different background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. Signal cross sections are enhanced by a factor of 20. |
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Figure 3-a:
Mass distribution of the reconstructed top quark candidate in the muon channel after the baseline selection. The different background contributions are shown using full histograms while the open histograms is signal yield and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. Signal cross sections are enhanced by a factor of 20. |
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Figure 3-b:
$ {p_{\mathrm {T}}} $ distribution of the reconstructed top quark candidate in the muon channel after the baseline selection. The different background contributions are shown using full histograms while the open histograms is signal yield and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. Signal cross sections are enhanced by a factor of 20. |
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Figure 4:
Vector-like T quark candidate mass in the signal region for the electron (left) and muon (right) channels. The different background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6. |
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Figure 4-a:
Vector-like T quark candidate mass in the signal region for the electron channel. The different background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6. |
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Figure 4-b:
Vector-like T quark candidate mass in the signal region for the muon channel. The different background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6. |
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Figure 5:
Selection efficiency $\epsilon _\text {sel}$ for the signal, i.e. the product of the branching fractions for the top quark decaying to final states including a lepton, and the Higgs boson decaying to bottom quarks, amounting to approximately 8%, is included in the signal selection efficiency. Left-handed (denoted by lh) and right-handed (denoted by rh) couplings of the T quark to SM particles in associated production with bottom and top quarks, respectively, are shown separately. |
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Figure 6:
Vector-like T quark candidate mass in the control region for the electron (left ) and muon (right ) channels. Signal samples are normalized to 20 pb, which is a factor of 20 larger than what is used in Figure 4. The shape of the data distribution provides the background estimate. The different background contributions are shown using full histograms while the open histogram are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. |
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Figure 6-a:
Vector-like T quark candidate mass in the control region for the electron channel. The signal sample is normalized to 20 pb, which is a factor of 20 larger than what is used in Figure 4. The shape of the data distribution provides the background estimate. The different background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. |
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Figure 6-b:
Vector-like T quark candidate mass in the control region for the muon channel. The signal sample is normalized to 20 pb, which is a factor of 20 larger than what is used in Figure 4. The shape of the data distribution provides the background estimate. The different background contributions are shown using full histograms while the open histograms are signal yields and the data are shown as solid circles. The hatched bands represent the statistical and systematic uncertainties of the simulated event samples. The systematic uncertainties include those discussed in Section 6, except the forward jet uncertainty. |
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Figure 7:
Shape comparison of the T quark candidate mass distributions in the signal (open histogram) and control (shaded histogram) regions for the electron (left ) and muon (right ) channels. The distributions show the sum of all simulated backgrounds, with the statistical uncertainties indicated as the error bars (signal region) or the hatched band (control region). |
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Figure 7-a:
Shape comparison of the T quark candidate mass distributions in the signal (open histogram) and control (shaded histogram) regions for the electron channel. The distribution shows the sum of all simulated backgrounds, with the statistical uncertainties indicated as the error bars (signal region) or the hatched band (control region). |
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Figure 7-b:
Shape comparison of the T quark candidate mass distributions in the signal (open histogram) and control (shaded histogram) regions for the muon channel. The distribution shows the sum of all simulated backgrounds, with the statistical uncertainties indicated as the error bars (signal region) or the hatched band (control region). |
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Figure 8:
Shape comparison of the ${\mathrm {T}}$ quark candidate mass distributions in the control region (shaded histogram) regions and the validation regions A (green) and B (blue) for the electron (left) and muon (right) channels in data. |
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Figure 8-a:
Shape comparison of the ${\mathrm {T}}$ quark candidate mass distributions in the control region (shaded histogram) regions and the validation regions A (green) and B (blue) for the electron channel in data. |
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Figure 8-b:
Shape comparison of the ${\mathrm {T}}$ quark candidate mass distributions in the control region (shaded histogram) regions and the validation regions A (green) and B (blue) for the muon channel in data. |
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Figure 9:
Final background, data, and expected signal distributions in $ {M_\mathrm {T}} $ in the signal region for the electron (left) and muon (right) channels. The normalisation of the background estimate is taken from the fit, its uncertainty is 12%. The hatched uncertainty band shows the statistical uncertainty in the background prediction, which is used as the shape uncertainty in the fit, as detailed in Section 6. |
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Figure 9-a:
Final background, data, and expected signal distributions in $ {M_\mathrm {T}} $ in the signal region for the electron channel. The normalisation of the background estimate is taken from the fit, its uncertainty is 12%. The hatched uncertainty band shows the statistical uncertainty in the background prediction, which is used as the shape uncertainty in the fit, as detailed in Section 6. |
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Figure 9-b:
Final background, data, and expected signal distributions in $ {M_\mathrm {T}} $ in the signal region for the muon channel. The normalisation of the background estimate is taken from the fit, its uncertainty is 12%. The hatched uncertainty band shows the statistical uncertainty in the background prediction, which is used as the shape uncertainty in the fit, as detailed in Section 6. |
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Figure 10:
Exclusion limits on the product of the cross section and the branching fraction of single T quark production and $ {\mathrm {T}} \to \mathrm{ t } \mathrm{ H } $ decay. A simultaneous fit is made to the electron and muon channels. Left- (right-) handed T quark production in association with a bottom (top) quark is shown in the left- (right-) diagram. |
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Figure 10-a:
Exclusion limits on the product of the cross section and the branching fraction of single T quark production and $ {\mathrm {T}} \to \mathrm{ t } \mathrm{ H } $ decay. A simultaneous fit is made to the electron and muon channels. The left-handed T quark production in association with a bottom quark is shown. |
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Figure 10-b:
Exclusion limits on the product of the cross section and the branching fraction of single T quark production and $ {\mathrm {T}} \to \mathrm{ t } \mathrm{ H } $ decay. A simultaneous fit is made to the electron and muon channels. The right-handed T quark production in association with a top quark is shown. |
| Tables | |
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Table 1:
Event selection criteria: required number of b-tagged subjets for the Higgs boson candidate, and number of forward jets. |
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Table 2:
Number of selected events $N_\text {sel}$ and selection efficiency $\epsilon _\text {sel}$ for the signal region including both statistical (stat) and systematic (sys) uncertainties. For the background, the post-fit value (as described in Sections {background} and \ref {sec_limits}) is quoted. The left- (right-) handed T quark production in association with a bottom (top) quark is denoted by a subscript lh (rh) and following b (t). All signal samples are normalised to a cross section of 1 pb, i.e. the product of the branching fractions for the top quark decaying to final states including a lepton, and the Higgs boson decaying to bottom quarks, amounting to approximately 8%, is included in the signal selection efficiency. |
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Table 3:
Impacts of the largest systematic uncertainties in the signal event yields. The signal samples for $ {\mathrm {T}} _\mathrm {lh}\mathrm{ b } $ production are shown. The uncertainties in the forward jet, and lepton isolation and trigger are rate uncertainties, all other uncertainties are evaluated bin-by-bin. All values are reported as percentage of the signal event yield. |
| Summary |
| A search for a singly produced vector-like T quark decaying to a top quark and a Higgs boson has been presented, where the top quark decay includes an electron or a muon and the Higgs boson decays into a pair of b quarks. For every event, the four-momentum of the vector-like T quark candidate is reconstructed and its mass is evaluated. No excess over the estimated backgrounds is observed. Upper limits are placed on the product of the cross section and the branching fraction for vector-like T quarks to third-generation standard model quarks in the mass range of 700 to 1800 GeV, at 95% confidence level. This is the first analysis setting exclusion limits on the cross section of singly produced vector-like T quarks at a centre-of-mass energy of 13 TeV. |
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