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| CMS-B2G-20-010 ; CERN-EP-2021-223 | ||
| Search for a heavy resonance decaying into a top quark and a W boson in the lepton+jets final state at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 19 November 2021 | ||
| JHEP 04 (2022) 048 | ||
| Abstract: A search for a heavy resonance decaying into a top quark and a W boson in proton-proton collisions at $\sqrt{s} = $ 13 TeV is presented. The data analyzed were recorded with the CMS detector at the LHC and correspond to an integrated luminosity of 138 fb$^{-1}$. The top quark is reconstructed as a single jet and the W boson, from its decay into an electron or muon and the corresponding neutrino. A top quark tagging technique based on jet clustering with a variable distance parameter and simultaneous jet grooming is used to identify jets from the collimated top quark decay. The results are interpreted in the context of two benchmark models, where the heavy resonance is either an excited bottom quark b* or a vector-like quark B. A statistical combination with an earlier search by the CMS Collaboration in the all-hadronic final state is performed to place upper cross section limits on these two models. The new analysis extends the lower range of resonance mass probed from 1.4 down to 0.7 TeV. For left-handed, right-handed, and vector-like couplings, b* masses up to 3.0, 3.0, and 3.2 TeV are excluded at 95% confidence level, respectively. The observed upper limits represent the most stringent constraints on the b* model to date. | ||
| Links: e-print arXiv:2111.10216 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Example Feynman diagrams at LO of the production and decay of a {\mathrm{b} ^\ast} (left) and a \PB quark (right), drawn with the TikZ-Feynman package [10]. |
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Figure 1-a:
Example Feynman diagram at LO of the production and decay of a b* quark, drawn with the TikZ-Feynman package [10]. |
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Figure 1-b:
Example Feynman diagram at LO of the production and decay of a B quark, drawn with the TikZ-Feynman package [10]. |
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Figure 2:
Distributions of ${M_{\mathrm{t} \mathrm{W}}}$ in the 1b (left) and 2b (right) categories. The data are shown by filled markers, where the horizontal bars indicate the bin widths. The individual background contributions are given by filled histograms. The expected signal for an LH b* with a mass of $m_{{\mathrm{b} ^*}} = $ 2.4 TeV is shown by a dashed line. The shaded region is the uncertainty in the total background estimate. The lower panels of each figure show the ratio of data to the background estimate, with the total uncertainty in the predicted background displayed as shaded band. |
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Figure 2-a:
Distribution of ${M_{\mathrm{t} \mathrm{W}}}$ in the 1b category. The data are shown by filled markers, where the horizontal bars indicate the bin widths. The individual background contributions are given by filled histograms. The expected signal for an LH b* with a mass of $m_{{\mathrm{b} ^*}} = $ 2.4 TeV is shown by a dashed line. The shaded region is the uncertainty in the total background estimate. The lower panel shows the ratio of data to the background estimate, with the total uncertainty in the predicted background displayed as shaded band. |
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Figure 2-b:
Distribution of ${M_{\mathrm{t} \mathrm{W}}}$ in the 2b category. The data are shown by filled markers, where the horizontal bars indicate the bin widths. The individual background contributions are given by filled histograms. The expected signal for an LH b* with a mass of $m_{{\mathrm{b} ^*}} = $ 2.4 TeV is shown by a dashed line. The shaded region is the uncertainty in the total background estimate. The lower panel shows the ratio of data to the background estimate, with the total uncertainty in the predicted background displayed as shaded band. |
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Figure 3:
Upper limits on the product of production cross section and branching fraction of the left-handed (upper left), right-handed (upper right) and vector-like (lower) b* hypotheses at 95% CL. Colored lines show the expected limits from the $\ell$+jets (dotted) and all-hadronic (dash-dotted) channels, where the latter start at b* masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits. The theoretical cross sections are shown as the red lines, where the uncertainties due to missing higher orders are depicted by shaded areas. |
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Figure 3-a:
Upper limits on the product of production cross section and branching fraction of the left-handed b* hypothesis at 95% CL. Colored lines show the expected limits from the $\ell$+jets (dotted) and all-hadronic (dash-dotted) channels, where the latter start at b* masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits. The theoretical cross section is shown as the red line, where the uncertainties due to missing higher orders are depicted by the shaded area. |
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Figure 3-b:
Upper limits on the product of production cross section and branching fraction of the right-handed b* hypothesis at 95% CL. Colored lines show the expected limits from the $\ell$+jets (dotted) and all-hadronic (dash-dotted) channels, where the latter start at b* masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits. The theoretical cross section is shown as the red line, where the uncertainties due to missing higher orders are depicted by the shaded area. |
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Figure 3-c:
Upper limits on the product of production cross section and branching fraction of the vector-like b* hypothesis at 95% CL. Colored lines show the expected limits from the $\ell$+jets (dotted) and all-hadronic (dash-dotted) channels, where the latter start at b* masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits. The theoretical cross section is shown as the red line, where the uncertainties due to missing higher orders are depicted by the shaded area. |
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Figure 4:
Upper limits on the product of production cross section and branching fraction of the B+b (left) and B+t (right) production modes at 95% CL. Colored lines show the expected limits from the $\ell$+jets (dotted) and all-hadronic (dash-dotted) channels, where the latter start at B masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits. The theoretical cross sections are shown as the red and blue lines, where the uncertainties due to missing higher orders are depicted by shaded areas. |
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Figure 4-a:
Upper limits on the product of production cross section and branching fraction of the B+b production mode at 95% CL. Colored lines show the expected limits from the $\ell$+jets (dotted) and all-hadronic (dash-dotted) channels, where the latter start at B masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits. The theoretical cross sections are shown as the red and blue lines, where the uncertainties due to missing higher orders are depicted by shaded areas. |
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Figure 4-b:
Upper limits on the product of production cross section and branching fraction of the B+t production mode at 95% CL. Colored lines show the expected limits from the $\ell$+jets (dotted) and all-hadronic (dash-dotted) channels, where the latter start at B masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits. The theoretical cross section is shown as the red line, where the uncertainties due to missing higher orders are depicted by the shaded area. |
| Tables | |
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Table 1:
Summary of all considered sources of systematic uncertainties affecting the ${M_{\mathrm{t} \mathrm{W}}}$ distributions in the 1b and 2b categories of the $\ell$+jets channel. The source of the uncertainty is given in the first column. The second column indicates if the uncertainty results in a change of normalization or shape of the ${M_{\mathrm{t} \mathrm{W}}}$ distribution. The samples affected by a given uncertainty source are shown in the third column. The fourth column shows the impact of these uncertainties, estimated for an LH b* signal with a mass of 2.4 TeV. These are quantified by calculating the change in the fitted signal strength when a given parameter is displaced by $ \pm $1 standard deviation from its post-fit value, divided by the total uncertainty in the fitted signal. Uncertainties taken to be fully correlated across the three years are given in the upper part of the table. Uncertainties affecting both the $\ell$+jets and all-hadronic channels are marked by an asterisk. |
| Summary |
| A search for a heavy resonance decaying to tW in the final state with a lepton and a t-tagged jet has been presented. The data analyzed correspond to an integrated luminosity of 138 fb$^{-1}$ of proton-proton collisions collected at a center-of-mass energy of 13 TeV. Final states where the W boson decays leptonically and the top quark decay results in a single jet are probed. Compared to an earlier analysis of the all-hadronic final state, the lower reach of the analysis is extended from 1.4 down to 0.7 TeV, because of lower lepton trigger thresholds and the extended range in t quark transverse momentum provided by the Heavy Object Tagger with Variable R. Above 1.4 TeV a combination with the search in the all-hadronic final state has been performed. The dominant $\mathrm{t\bar{t}}$ background is constrained using a dedicated control region and the background from misidentified t jets is estimated from data. No significant excess of data over the background prediction is observed. Upper limits on the single production of a vector-like quark decaying to tW have been derived in the mass range of 0.7 to 1.8 TeV. The excited bottom quark b* hypotheses with left-handed, right-handed, and vector-like chiralities are excluded at 95% confidence level up to masses of 3.0, 3.0, and 3.2 TeV, respectively. The upper limits on the product of cross section and branching fraction represent the most stringent constraints on the b* model to date. |
| Additional Figures | |
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Additional Figure 1:
Distribution of $\alpha $ as a function of $M_{{\mathrm {t}} {\mathrm {W}}}$ for the background estimation in the 1b category. Two different parametrizations are fitted to the distributions (solid lines) and the total uncertainty is shown as colored area. |
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Additional Figure 2:
Distribution of $\alpha $ as a function of $M_{{\mathrm {t}} {\mathrm {W}}}$ for the background estimation in the 2b category. Two different parametrizations are fitted to the distributions (solid lines) and the total uncertainty is shown as colored area. |
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