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| CMS-B2G-19-003 ; CERN-EP-2021-044 | ||
| 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 | ||
| 26 April 2021 | ||
| JHEP 12 (2021) 106 | ||
| 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 data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb$^{-1}$ recorded by the CMS experiment at the LHC. The search 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. The production of an excited bottom quark, ${\mathrm{b}^\ast} $, is used as a benchmark 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 chiralities are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1 TeV, respectively. These are the most stringent limits on the ${\mathrm{b}^\ast} $ quark mass to date, extending the previous best limits by almost a factor of two. | ||
| Links: e-print arXiv:2104.12853 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The efficiency of the full trigger selection as a function of $ {m_{\mathrm {jj}}} $, shown separately for 2016, 2017, and 2018 data. The minimum $ {m_{\mathrm {jj}}} $ considered in the analysis is 1200 GeV and is marked with a dashed line and an arrow. The efficiency below $ {m_{\mathrm {jj}}} $ of 1000 GeV is not measured. The points for 2017 and 2018 data are not visible in the plateau because they are overlapped by the points for 2016 data. |
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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 $ {\mathrm{b} ^\ast} $ signal sample is represented with the solid line. The area of the total background contribution and the 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 optimized selection used for events in the signal region. For the $ {\mathrm{b} ^\ast} $ signal sample, the top tag soft-drop mass spectrum exhibits a resonance near the W mass, which is comprised of W jets that have been misidentified as top jets. |
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Figure 2-a:
Distribution of the top jet $\tau _3/\tau _2$ for simulation samples. This discrimination variable is used for W and top tagging. The $ {\mathrm{b} ^\ast} $ signal sample is represented with the solid line. The area of the total background contribution and the 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 optimized selection used for events in the signal region. |
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Figure 2-b:
Distribution of the W jet $\tau _2/\tau _1$ for simulation samples. This discrimination variable is used for W and top tagging.The $ {\mathrm{b} ^\ast} $ signal sample is represented with the solid line. The area of the total background contribution and the 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 optimized selection used for events in the signal region. |
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Figure 2-c:
Distribution of the top tag soft-drop mass for simulation samples. This discrimination variable is used for W and top tagging.The $ {\mathrm{b} ^\ast} $ signal sample is represented with the solid line. The area of the total background contribution and the 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 optimized selection used for events in the signal region. For the $ {\mathrm{b} ^\ast} $ signal sample, the top tag soft-drop mass spectrum exhibits a resonance near the W mass, which is comprised of W jets that have been misidentified as top jets. |
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Figure 2-d:
Distribution of the W tag soft-drop mass for simulation samples. This discrimination variable is used for W and top tagging. The $ {\mathrm{b} ^\ast} $ signal sample is represented with the solid line. The area of the total background contribution and the 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 optimized selection used for events in the signal region. |
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Figure 2-e:
Distribution of the subjet b-tagging discriminant for simulation samples. This discrimination variable is used for W and top tagging. The $ {\mathrm{b} ^\ast} $ signal sample is represented with the solid line. The area of the total background contribution and the 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 optimized selection used for events in the signal region. |
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Figure 3:
Distributions of $ {m_{\mathrm{t}}} $ in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ measurement region for three intervals of $ {m_{\mathrm{t} \mathrm{t}}} $: 1200-1300 GeV (upper), 1300-1800 GeV (middle), 1800-3000 GeV (lower). The data are shown by points with error bars and the individual background contributions by filled histograms. The signal is not visible because the contamination in this region is negligible. The barely visible 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 requirement, respectively. The lower panels of each figure show the pull, as a function of $ {m_{\mathrm{t}}} $, defined as the difference between the number of events observed in the data and the predicted background, divided by their combined uncertainty. |
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Figure 4:
Distributions of $ {m_{{\mathrm{t} \mathrm{W}}}} $ in the $ {\mathrm{b} ^\ast} $ signal region for three intervals of $ {m_{\mathrm{t}}} $: 65-105 GeV (upper), 105-225 GeV (middle), and 225-285 GeV (lower). The data are shown by points with error bars, the individual background contributions by filled histograms, and a 2.4 TeV $ {\mathrm{b} ^\ast _{\mathrm {LH}}} $ signal is shown as a solid line. The barely visible 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 requirement, respectively. The lower panels of each figure show the pull, as a function of $ {m_{{\mathrm{t} \mathrm{W}}}} $, defined as the difference between the number of events observed in the data and the predicted background, divided by their combined uncertainty. |
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Figure 5:
Upper limits on the product of the cross section and branching fraction at 95% CL for a $ {\mathrm{b} ^\ast _{\mathrm {LH}}} $ (upper), $ {\mathrm{b} ^\ast _{\mathrm {RH}}} $ (middle), and $ {\mathrm{b} ^\ast _{\mathrm {LH+RH}}} $ (lower) quark as a function of the $ {\mathrm{b} ^\ast} $ quark mass. The expected (dashed) and observed (dot-solid) limits, as well as the $ {\mathrm{b} ^\ast} $ quark theoretical cross sections (shaded-solid), are shown. The vertical dashed lines indicate the intersection of the theoretical cross sections with the expected and observed limits. The inner and outer shaded areas around the expected limits show the 68% and 95% CL intervals, respectively. |
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Figure 5-a:
Upper limits on the product of the cross section and branching fraction at 95% CL for a $ {\mathrm{b} ^\ast _{\mathrm {LH}}} $ quark as a function of the $ {\mathrm{b} ^\ast} $ quark mass. The expected (dashed) and observed (dot-solid) limits, as well as the $ {\mathrm{b} ^\ast} $ quark theoretical cross sections (shaded-solid), are shown. The vertical dashed lines indicate the intersection of the theoretical cross sections with the expected and observed limits. The inner and outer shaded areas around the expected limits show the 68% and 95% CL intervals, respectively. |
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Figure 5-b:
Upper limits on the product of the cross section and branching fraction at 95% CL for a $ {\mathrm{b} ^\ast _{\mathrm {RH}}} $ quark as a function of the $ {\mathrm{b} ^\ast} $ quark mass. The expected (dashed) and observed (dot-solid) limits, as well as the $ {\mathrm{b} ^\ast} $ quark theoretical cross sections (shaded-solid), are shown. The vertical dashed lines indicate the intersection of the theoretical cross sections with the expected and observed limits. The inner and outer shaded areas around the expected limits show the 68% and 95% CL intervals, respectively. |
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Figure 5-c:
Upper limits on the product of the cross section and branching fraction at 95% CL for a $ {\mathrm{b} ^\ast _{\mathrm {LH+RH}}} $ quark as a function of the $ {\mathrm{b} ^\ast} $ quark mass. The expected (dashed) and observed (dot-solid) limits, as well as the $ {\mathrm{b} ^\ast} $ quark theoretical cross sections (shaded-solid), are shown. The vertical dashed lines indicate the intersection of the theoretical cross sections with the expected and observed limits. The inner and outer shaded areas around the expected limits show the 68% and 95% CL intervals, respectively. |
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Figure 6:
Upper limits on the product of the cross section and branching fraction at 95% CL for a B produced in association with a bottom quark (left) and top quark (right) as a function of the B quark mass. The expected (dashed) and observed (dot-solid) limits, as well as the B quark theoretical cross sections (shaded-solid), are shown. The inner and outer shaded areas around the expected limits show the 68% and 95% CL intervals, respectively. |
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Figure 6-a:
Upper limits on the product of the cross section and branching fraction at 95% CL for a B produced in association with a bottom quark as a function of the B quark mass. The expected (dashed) and observed (dot-solid) limits, as well as the B quark theoretical cross sections (shaded-solid), are shown. The inner and outer shaded areas around the expected limits show the 68% and 95% CL intervals, respectively. |
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Figure 6-b:
Upper limits on the product of the cross section and branching fraction at 95% CL for a B produced in association with a top quark as a function of the B quark mass. The expected (dashed) and observed (dot-solid) limits, as well as the B quark theoretical cross sections (shaded-solid), are shown. The inner and outer shaded areas around the expected limits show the 68% and 95% CL intervals, respectively. |
| Tables | |
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Table 1:
A summary of the four selection regions considered in the likelihood fit to data. The columns indicate the possible jet tag for the jet considered in the preselection while the rows indicate the possible classification of the second jet when using the top tagging algorithm. |
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Table 2:
Sources of uncertainty that are taken into account in the statistical analysis of the data. The sources affecting the normalization are given with their percentage uncertainties, while the sources affecting the shape are listed as "Shape'' together with the dependent parameter. The rightmost column indicates the impact of the parameter on the 2.4 TeV b* 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 $+$0.0 ($-$0.0) denotes an impact that is less (greater) than 0.1 ($-$0.1) but greater (less) than 0. |
| Summary |
|
A search for a heavy resonance decaying to a top quark and a W boson in the fully hadronic final state has been presented. The analysis uses proton-proton collision data at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 137 fb$^{-1}$ , collected by the CMS experiment at the LHC during 2016-2018. This analysis considers the explicit case where the heavy resonance is an excited bottom quark, ${\mathrm{b}^\ast} $. The search evaluates ${\mathrm{b}^\ast} $ quark masses greater than 1.2 TeV, which result in highly Lorentz-boosted top quarks and W bosons that 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 a W boson jet, respectively. The background processes in the analysis are a result of multijet processes from the strong interaction, $\mathrm{t\bar{t}}$ production, and single top quark (tW-channel) production. The search is performed using a two-dimensional binned likelihood fit to the data that allows all backgrounds to be fit simultaneously. The multijet component in the signal region is estimated via a two-dimensional transfer function method that uses a multijet-enriched control region. The $\mathrm{t\bar{t}}$ and single top background estimates are determined 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. 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 chiralities are excluded at 95% confidence level for masses below 2.6, 2.8, and 3.1 TeV, respectively. These are the most stringent limits on the ${\mathrm{b}^\ast} $ quark mass to date, extending the previous best mass limits by almost a factor of two. |
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