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| CMS-PAS-B2G-19-003 | ||
| Search for a heavy resonance decaying to a top quark and a W boson at $\sqrt{s} = $ 13 TeV in the fully hadronic final state | ||
| CMS Collaboration | ||
| January 2021 | ||
| Abstract: A search for a heavy resonance decaying to a top quark and a W boson in the fully hadronic final state is presented. The analysis is performed using proton-proton collisions at a center-of-mass energy of 13 TeV. The search uses data corresponding to an integrated luminosity of 137 fb$^{-1}$ recorded by the CMS experiment at the LHC. The analysis is focused on heavy resonances, where the decay products of each top quark or W boson are expected to be reconstructed as a single, large radius jet with a distinct substructure. An excited bottom quark, $\mathrm{b}^\ast$, is used as a benchmark model when setting limits on the cross section for a heavy resonance decaying to a top quark and a W boson. The hypotheses of $\mathrm{b}^\ast$ quarks with left-handed, right-handed, and vector-like chirality are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1 TeV, respectively. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
The efficiency of the triggers as a function of $ {m_{{\mathrm {t}\mathrm{W}}}} $, extracted from 2016 (black), 2017 (green), and 2018 (yellow) data. The minimum $ {m_{{\mathrm {t}\mathrm{W}}}} $ considered in the analysis is 1200 GeV and is marked with a dashed line and an arrow. The efficiency below $ {m_{{\mathrm {t}\mathrm{W}}}} $ of 1000 GeV is not measured. |
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Figure 2:
The distributions of the discrimination variables used for W and top tagging for simulation samples. These plots show the top jet $\tau _3/\tau _2$ (upper-left), the W jet $\tau _2/\tau _1$ (upper-right), the top tag soft-drop mass (middle-left), the W tag soft-drop mass (middle-right), and the subjet b-tagging discriminant (lower). The area of the total background contribution and area of the signal component are separately normalized to unity. All analysis selections are applied with the exception of the variable being plotted. Also shown are vertical dashed lines and arrows, which indicate the selection used for events in the signal region. |
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Figure 2-a:
The distributions of the discrimination variables used for W and top tagging for simulation samples. These plots show the top jet $\tau _3/\tau _2$. The area of the total background contribution and area of the signal component are separately normalized to unity. All analysis selections are applied with the exception of the variable being plotted. Also shown are vertical dashed lines and arrows, which indicate the selection used for events in the signal region. |
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Figure 2-b:
The distributions of the discrimination variables used for W and top tagging for simulation samples. These plots show the W jet $\tau _2/\tau _1$. The area of the total background contribution and area of the signal component are separately normalized to unity. All analysis selections are applied with the exception of the variable being plotted. Also shown are vertical dashed lines and arrows, which indicate the selection used for events in the signal region. |
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Figure 2-c:
The distributions of the discrimination variables used for W and top tagging for simulation samples. These plots show the top tag soft-drop mass. The area of the total background contribution and area of the signal component are separately normalized to unity. All analysis selections are applied with the exception of the variable being plotted. Also shown are vertical dashed lines and arrows, which indicate the selection used for events in the signal region. |
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Figure 2-d:
The distributions of the discrimination variables used for W and top tagging for simulation samples. These plots show the W tag soft-drop mass. The area of the total background contribution and area of the signal component are separately normalized to unity. All analysis selections are applied with the exception of the variable being plotted. Also shown are vertical dashed lines and arrows, which indicate the selection used for events in the signal region. |
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Figure 2-e:
The distributions of the discrimination variables used for W and top tagging for simulation samples. These plots show the subjet b-tagging discriminant. The area of the total background contribution and area of the signal component are separately normalized to unity. All analysis selections are applied with the exception of the variable being plotted. Also shown are vertical dashed lines and arrows, which indicate the selection used for events in the signal region. |
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Figure 3:
Distributions in $ {m_{\mathrm {t}}} $ in the ${\mathrm{t} {}\mathrm{\bar{t}}} $ measurement region for three intervals of $ {m_{\mathrm {tt}}} $. The intervals in $ {m_{\mathrm {tt}}} $ are 1200 $ < {m_{\mathrm {tt}}} < $ 1300 GeV (upper), 1300 $ < {m_{\mathrm {tt}}} < $ 1800 GeV (middle), and 1800 $ < {m_{\mathrm {tt}}} < $ 3000 GeV (lower). The data are shown by closed markers, the individual background contributions by filled histograms. The signal is not visible because the contamination in this region is negligible. The shaded region is the uncertainty in the total background estimate. The left and right columns show distributions for events with a jet failing and passing the top tagging requirements, respectively. The lower panels of each figure show the pull, as a function of $ {m_{\mathrm {t}}} $, as defined in the text. |
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Figure 4:
Distributions in $ {m_{{\mathrm {t}\mathrm{W}}}} $ in the $ {\mathrm {b}^\ast} $ signal region for three intervals of $ {m_{\mathrm {t}}} $. The intervals in $ {m_{\mathrm {t}}} $ are 65 $ < {m_{\mathrm {t}}} < $ 105 GeV (upper), 105 $ < {m_{\mathrm {t}}} < $ 225 GeV (middle), and 225 $ < {m_{\mathrm {t}}} < $ 285 GeV (lower). The data are shown by closed markers, the individual background contributions by filled histograms, and a 2400 GeV $ {\mathrm {b}^\ast _{\mathrm {LH}}}$ signal is shown as a solid line. The shaded region is the uncertainty in the total background estimate. The left and right columns show distributions for events with a jet failing and passing the top tagging requirements, respectively. The lower panels of each figure show the pull, as a function of $ {m_{{\mathrm {t}\mathrm{W}}}} $, as defined in the text. |
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Figure 5:
Upper limits on the production cross section times branching fraction at 95% CL for a $ {\mathrm {b}^\ast _{\mathrm {LH}}} $ (top), $ {\mathrm {b}^\ast _{\mathrm {RH}}} $ (middle), and $ {\mathrm {b}^\ast _{\mathrm {LH+RH}}} $ (bottom) as a function of $ {\mathrm {b}^\ast} $ mass. The expected (dashed) limits, the observed (dot-solid) limit, and $ {\mathrm {b}^\ast} $ quark theoretical cross section (shaded-solid) are shown. The vertical dashed lines indicate the intersection of theory curve with the expected and observed limits. The colored areas around the expected limit show the 68 and 95% confidence level intervals. |
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Figure 5-a:
Upper limits on the production cross section times branching fraction at 95% CL for a $ {\mathrm {b}^\ast _{\mathrm {LH}}} $ as a function of $ {\mathrm {b}^\ast} $ mass. The expected (dashed) limits, the observed (dot-solid) limit, and $ {\mathrm {b}^\ast} $ quark theoretical cross section (shaded-solid) are shown. The vertical dashed lines indicate the intersection of theory curve with the expected and observed limits. The colored areas around the expected limit show the 68 and 95% confidence level intervals. |
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Figure 5-b:
Upper limits on the production cross section times branching fraction at 95% CL for a $ {\mathrm {b}^\ast _{\mathrm {RH}}} $ as a function of $ {\mathrm {b}^\ast} $ mass. The expected (dashed) limits, the observed (dot-solid) limit, and $ {\mathrm {b}^\ast} $ quark theoretical cross section (shaded-solid) are shown. The vertical dashed lines indicate the intersection of theory curve with the expected and observed limits. The colored areas around the expected limit show the 68 and 95% confidence level intervals. |
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Figure 5-c:
Upper limits on the production cross section times branching fraction at 95% CL for a $ {\mathrm {b}^\ast _{\mathrm {LH+RH}}} $ as a function of $ {\mathrm {b}^\ast} $ mass. The expected (dashed) limits, the observed (dot-solid) limit, and $ {\mathrm {b}^\ast} $ quark theoretical cross section (shaded-solid) are shown. The vertical dashed lines indicate the intersection of theory curve with the expected and observed limits. The colored areas around the expected limit show the 68 and 95% confidence level intervals. |
| Tables | |
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Table 1:
Selection efficiencies for inclusive $ {\mathrm {b}^\ast} $ signal samples at various generated masses and the left-handed and right-handed chiralities. |
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Table 2:
Sources of uncertainty that are taken into account in the statistical analysis of the data. A percentage is listed for normalization uncertainties while the variables affecting the shape are indicated with "Shape'' and the variable in which the parameter is changing. The rightmost column indicates the impact of the parameter on the 2400 GeV $ {\mathrm {b}^\ast}$ signal strength when the parameter is changed "up'' and "down'' by one standard deviation from its post-fit value. For parameters where the uncertainties are uncorrelated between data-taking years, the average impact is calculated. An impact of $+$0.0 ($-$0.0) denotes an impact that is less (greater) than $+$0.1 ($-$0.1) but greater (less) than 0. |
| Summary |
|
A search for a heavy resonances decaying to a top quark and a W boson in the fully hadronic final state has been presented. The analysis uses proton-proton collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 137 fb$^{-1}$, collected with the CMS experiment at the LHC during 2016, 2017, and 2018. The search considers ${\mathrm{b}^\ast} $ quark masses greater than 1.2 TeV, which results in highly Lorentz-boosted top quarks and W bosons, which are reconstructed as single jets. Using jet substructure algorithms designed to distinguish heavy resonance decays from light-quark and gluon jets, the top quark and W boson decays are identified as a top quark jet and W jet, respectively. The main backgrounds in the analysis are multijet processes from the strong interaction and $\mathrm{t\bar{t}}$ production. These are simultaneously estimated from a control sample in data. The $\mathrm{t\bar{t}}$ and single top quark (tW-channel) production are estimated via a template fit to data. In particular, a dedicated $\mathrm{t\bar{t}}$ measurement region is used to constrain the shape and yield of the $\mathrm{t\bar{t}}$ background. The multijet component is estimated via a two-dimensional transfer function method that uses a multijet-enriched control region to estimate the multijet background in the signal region. The search is performed as a two-dimensional binned likelihood fit of the data which allows all backgrounds to be fit simultaneously. No statistically significant deviation from the standard model expectation is observed. The hypotheses of ${\mathrm{b}^\ast} $ quarks with left-handed, right-handed, and vector-like chirality are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1TeV, respectively. These are the most stringent limits on the ${\mathrm{b}^\ast} $ quark mass to date, significantly extending the previous best limits by almost a factor of two. |
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