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| CMS-PAS-B2G-16-009 | ||
| Search for W' $\to$ tb in pp collisions at $\sqrt{s} =$ 13 TeV | ||
| CMS Collaboration | ||
| August 2016 | ||
| Abstract: A search is performed for the production of a massive W' boson decaying to a top and a bottom quark. The data analyzed correspond to an integrated luminosity of 2.55 fb$^{-1}$ collected with the CMS detector at the LHC in proton-proton collisions at $\sqrt{s}=$ 13 TeV. The hadronic decay products of the top quark produced in the W' boson decay with high Lorentz boost are detected as a single top-flavored jet. The use of jet substructure algorithms allows the top quark jet to be distinguished from standard model QCD multi-jet background. The production of a right-handed W' boson with a mass below 2.0 TeV decaying to a hadronic final state is excluded at 95% confidence level. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1-a:
The average b tagging rate for QCD jets parameterized as a function of $ {p_{\mathrm {T}}} $ from the low (a), transition (b), and high (c) $|\eta |$ regions. The measured average b tagging rate is represented by the data points, the polynomial fit is shown as a solid line, and the propagated uncertainties from the fit are shown as the dashed lines. |
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Figure 1-b:
The average b tagging rate for QCD jets parameterized as a function of $ {p_{\mathrm {T}}} $ from the low (a), transition (b), and high (c) $|\eta |$ regions. The measured average b tagging rate is represented by the data points, the polynomial fit is shown as a solid line, and the propagated uncertainties from the fit are shown as the dashed lines. |
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Figure 1-c:
The average b tagging rate for QCD jets parameterized as a function of $ {p_{\mathrm {T}}} $ from the low (a), transition (b), and high (c) $|\eta |$ regions. The measured average b tagging rate is represented by the data points, the polynomial fit is shown as a solid line, and the propagated uncertainties from the fit are shown as the dashed lines. |
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Figure 2:
MC-only comparison of $ {M_{\mathrm {tb}}} $ in the signal region for demonstrating that the QCD background shape can be determined correctly using the b tagging rate method described in the text. The data points are the summed QCD, single top, and $ {\mathrm {t}\overline {\mathrm {t}}} $ signal regions, representing an approximation of the signal region in data given the null signal hypothesis. The bottom plot shows the pull ((data-background)/$\sigma $) between the data and the background estimate distributions. All distributions are normalized to the expected number of events. |
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Figure 3:
Distribution of $ {M_{\mathrm {tb}}} $ in the inverted subjet b tag control region defined in the text. The bottom plot shows the pull ((data-background)/$\sigma $) between the data and the background estimate distributions. All distributions are normalized to the expected number of events. |
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Figure 4:
Distribution of b candidate softdrop mass in the inverted b candidate softdrop mass control region defined in the text. This region is used to investigate the agreement of data and background, specifically with respect to the MC $ {\mathrm {t}\overline {\mathrm {t}}} $ estimate, which has an increased fraction in this region. The bottom plot shows the pull ((data-background)/$\sigma $) between the data and the background estimate distributions. All distributions are normalized to the expected number of events. |
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Figure 5-a:
The distribution of $ {M_{\mathrm {tb}}} $ in the signal region shown for data, data-derived QCD background, several MC background contributions, and several example signal W' boson MC samples. The W' signal and background MC samples are normalized to the cross section and the luminosity of the full dataset. The distributions are shown after the application of all selections, and are plotted using the background and uncertainty estimates from both before (top) and after (bottom) the limit setting fit. |
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Figure 5-b:
The distribution of $ {M_{\mathrm {tb}}} $ in the signal region shown for data, data-derived QCD background, several MC background contributions, and several example signal W' boson MC samples. The W' signal and background MC samples are normalized to the cross section and the luminosity of the full dataset. The distributions are shown after the application of all selections, and are plotted using the background and uncertainty estimates from both before (top) and after (bottom) the limit setting fit. |
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Figure 6:
The $ {\mathrm {W}^\prime _{\mathrm {R}}} $ boson 95% CL production cross section limits. The observed and expected limits, as well as $ {\mathrm {W}^\prime _{\mathrm {R}}} $ boson theoretical cross section are shown. The uncertainty in the expected limit band represents the 68% and 95% confidence intervals. |
| Tables | |
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Table 1:
The top tagging scale factor as parametrized in $ {p_{\mathrm {T}}} $. |
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Table 2:
Numbers of observed and expected events at successive stages of the event selection. The expected numbers are scaled to an integrated luminosity of 2.55 fb$^{-1}$. Statistical uncertainties in the event yields are quoted. The QCD background contribution is only reported for the final selection due to the fact that the data driven QCD estimate requires the b tagging and subjet b tagging selections be applied. The signal events, shown for several values of the W' boson mass, are normalized to the theoretical cross section. Scale factors are applied to rows after the corresponding selection is applied. |
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Table 3:
Sources of uncertainty that affect the $ {M_{\mathrm {tb}}} $ distribution that are taken into account when setting limits. Because of the low yield, shape uncertainties are neglected for single top. |
| Summary |
| A search for a new massive gauge boson W' decaying to a bottom quark and a hadronically decaying top quark is performed using pp collisions recorded by the CMS detector at $ \sqrt{s} = $ 13 TeV. The analysis uses jet substructure algorithms to allow the top quark jet to be distinguished from standard model hadronic jet backgrounds. The main background from QCD multi-jet production is estimated from data using the average b tagging rate measured in a QCD-enhanced control region. Limits are placed on the production cross section of a right-handed W' boson using 2.55 fb$^{-1}$ of luminosity. This is the first search in this channel at 13 TeV, and a right-handed W' with mass below 2.0 TeV is excluded at 95% CL. |
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