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| CMS-B2G-18-001 ; CERN-EP-2018-279 | ||
| Search for a W' boson decaying to a vector-like quark and a top or bottom quark in the all-jets final state | ||
| CMS Collaboration | ||
| 17 November 2018 | ||
| JHEP 03 (2019) 127 | ||
| Abstract: A search for a heavy W' resonance decaying to one B or T vector-like quark and a top or bottom quark, respectively, is presented. The search uses proton-proton collision data collected in 2016 with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$ at $\sqrt{s} = $ 13 TeV. Both decay channels result in a final state with a top quark, a Higgs boson, and a b quark, each produced with significant energy. The all-hadronic decays of both the Higgs boson and the top quark are considered. The final-state jets, some of which correspond to merged decay products of a boosted top quark and a Higgs boson, are selected using jet substructure techniques, which help to suppress standard model backgrounds. A W' boson signal would appear as a narrow peak in the invariant mass distribution of these jets. No significant deviation in data with respect to the standard model background predictions is observed. Cross section upper limits on W' boson production in the top quark, Higgs boson, and b quark decay mode are set as a function of the W' mass, for several vector-like quark mass hypotheses. These are the first limits for W' boson production in this decay channel, and cover a range of 0.01 to 0.43 pb in the W' mass range between 1.5 and 4.0 TeV. | ||
| Links: e-print arXiv:1811.07010 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The W' boson production and decays considered in the analysis. The analysis assumes equal branching fractions for W' boson to Bt and Tb and 50% for each VLQ to qH. |
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Figure 1-a:
A W' boson production and decay considered in the analysis. |
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Figure 1-b:
A W' boson production and decay considered in the analysis. |
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Figure 2:
Trigger efficiency as a function of $ {H_{\mathrm {T}}} $. Events are required to have $ {H_{\mathrm {T}}} > $ 1 TeV as is indicated by the red dashed line. The $ {H_{\mathrm {T}}} $ distributions of two W' signal hypotheses are shown for comparison, normalized to unit area. |
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Figure 3:
Normalized distributions of the discriminating variables in $ {{\mathrm {t}\overline {\mathrm {t}}}} $, QCD, and signal MC simulation. The distributions shown, from upper left to lower right, are of the variables: the maximum subjet b tag, $\tau _3$/$\tau _2$, and $m_{\mathrm {SD}}^ {\mathrm {t}}$, all used for top quark discrimination, and the double-b tag discriminant and $m_{\mathrm {SD}}^ {\mathrm {H}} $ used for tagging candidate Higgs boson jets. The QCD distributions are extracted from events with the generator-level $ {H_{\mathrm {T}}} > $ 1 TeV. Each variable distribution in this set of figures requires an event that passes the selection on all other variables in order to preserve possible correlations. |
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Figure 3-a:
Normalized distribution of the maximum subjet b tag, discriminating variable used for top quark discrimination, in $ {{\mathrm {t}\overline {\mathrm {t}}}} $, QCD, and signal MC simulation. The QCD distributions are extracted from events with the generator-level $ {H_{\mathrm {T}}} > $ 1 TeV. This variable distribution requires an event that passes the selection on other variables shown in Fig. 3 in order to preserve possible correlations. |
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Figure 3-b:
Normalized distribution of $\tau _3$/$\tau _2$, discriminating variable used for top quark discrimination, in $ {{\mathrm {t}\overline {\mathrm {t}}}} $, QCD, and signal MC simulation. The QCD distributions are extracted from events with the generator-level $ {H_{\mathrm {T}}} > $ 1 TeV. This variable distribution requires an event that passes the selection on other variables shown in Fig. 3 in order to preserve possible correlations. |
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Figure 3-c:
Normalized distribution of $m_{\mathrm {SD}}^ {\mathrm {t}}$, discriminating variable used for top quark discrimination, in $ {{\mathrm {t}\overline {\mathrm {t}}}} $, QCD, and signal MC simulation. The QCD distributions are extracted from events with the generator-level $ {H_{\mathrm {T}}} > $ 1 TeV. This variable distribution requires an event that passes the selection on other variables shown in Fig. 3 in order to preserve possible correlations. |
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Figure 3-d:
Normalized distribution of the double-b tag discriminant, discriminating variable used for tagging candidate Higgs boson jets, in $ {{\mathrm {t}\overline {\mathrm {t}}}} $, QCD, and signal MC simulation. The QCD distributions are extracted from events with the generator-level $ {H_{\mathrm {T}}} > $ 1 TeV. This variable distribution requires an event that passes the selection on other variables shown in Fig. 3 in order to preserve possible correlations. |
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Figure 3-e:
Normalized distribution of $m_{\mathrm {SD}}^ {\mathrm {H}} $, discriminating variable used for tagging candidate Higgs boson jets, in $ {{\mathrm {t}\overline {\mathrm {t}}}} $, QCD, and signal MC simulation. The QCD distributions are extracted from events with the generator-level $ {H_{\mathrm {T}}} > $ 1 TeV. This variable distribution requires an event that passes the selection on other variables shown in Fig. 3 in order to preserve possible correlations. |
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Figure 4:
Transfer function $ {F({p_{\mathrm {T}}},\eta)} $ used for estimation of the QCD background in the signal region, shown in the central (left) and forward (right) $\eta $ regions. The error bars represent the statistical uncertainty in $ {F({p_{\mathrm {T}}},\eta)} $ only. |
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Figure 4-a:
Transfer function $ {F({p_{\mathrm {T}}},\eta)} $ used for estimation of the QCD background in the signal region, shown in the central $\eta $ region. The error bars represent the statistical uncertainty in $ {F({p_{\mathrm {T}}},\eta)} $ only. |
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Figure 4-b:
Transfer function $ {F({p_{\mathrm {T}}},\eta)} $ used for estimation of the QCD background in the signal region, shown in the forward $\eta $ region. The error bars represent the statistical uncertainty in $ {F({p_{\mathrm {T}}},\eta)} $ only. |
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Figure 5:
Reconstructed W' mass distributions ($ {m_{\mathrm {{\mathrm {t}} {\mathrm {H}} {\mathrm {b}}}}} $) in the b candidate inverted validation region (VR) shown for data and background contributions. Several signal hypotheses are shown to demonstrate the low signal contamination. The background uncertainty includes all systematic and statistical uncertainties. |
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Figure 6:
Reconstructed W' mass distributions ($ {m_{\mathrm {{\mathrm {t}} {\mathrm {H}} {\mathrm {b}}}}} $) for the simulated QCD events in the signal region for the purposes of validation. The agreement given the systematic uncertainties is at the 1 standard deviation level. The background uncertainty takes into account all systematic and statistical uncertainties. |
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Figure 7:
Reconstructed W' mass distributions ($ {m_{\mathrm {{\mathrm {t}} {\mathrm {H}} {\mathrm {b}}}}} $) in the signal region, compared with the distributions of estimated backgrounds, and several benchmarks models. The signal distributions include the contributions from W' decays to both the $ {\mathrm {T}} $ and $ {\mathrm {B}} $ assuming equal branching fractions. The uncertainties shown in the hatched region contain both statistical and systematic uncertainties of all background components. |
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Figure 8:
The W' boson 95% CL production cross section limits. The expected limits (dashed) and observed limits (solid), as well as the W' boson theoretical cross section and the PDF and scale normalization uncertainties are shown. The bands around the expected limit represent the $\pm $1 and ${\pm}$2$\sigma _{exp}$ uncertainties in the expected limit. The limits for low- (upper left), medium- (upper right), and high- (lower) mass VLQ mass ranges, defined in Table 2, are shown. |
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Figure 8-a:
The W' boson 95% CL production cross section limits. The expected limits (dashed) and observed limits (solid), as well as the W' boson theoretical cross section and the PDF and scale normalization uncertainties are shown. The bands around the expected limit represent the $\pm $1 and ${\pm}$2$\sigma _{exp}$ uncertainties in the expected limit. The limits for low-mass VLQ mass ranges, defined in Table 2, are shown. |
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Figure 8-b:
The W' boson 95% CL production cross section limits. The expected limits (dashed) and observed limits (solid), as well as the W' boson theoretical cross section and the PDF and scale normalization uncertainties are shown. The bands around the expected limit represent the $\pm $1 and ${\pm}$2$\sigma _{exp}$ uncertainties in the expected limit. The limits for medium-mass VLQ mass ranges, defined in Table 2, are shown. |
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Figure 8-c:
The W' boson 95% CL production cross section limits. The expected limits (dashed) and observed limits (solid), as well as the W' boson theoretical cross section and the PDF and scale normalization uncertainties are shown. The bands around the expected limit represent the $\pm $1 and ${\pm}$2$\sigma _{exp}$ uncertainties in the expected limit. The limits for high-mass VLQ mass ranges, defined in Table 2, are shown. |
| Tables | |
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Table 1:
Selection regions used in the analysis. Tagging discriminator selections and regions described in the text are explicitly defined here. The signal region (SR) is used to set cross section upper limits, the control regions (CRN) are used to estimate the QCD background, and the validation region (VR) is used to validate the background estimation procedure. |
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Table 2:
The selection efficiency (%) for each signal mass point in the analysis. |
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Table 3:
Sources of systematic uncertainty affecting the $ {m_{\mathrm {{\mathrm {t}} {\mathrm {H}} {\mathrm {b}}}}} $ distribution. Sources that list the systematic variation as $ \pm$1$ \sigma $ depend on the distribution of the variable given in the parentheses, while those that list the variation in percent are rate uncertainties. |
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Table 4:
Event yield table after various selections. The definition of each region is given in Table 1. The uncertainties shown here for the validation region and the signal region are pre fit; the posteriori uncertainties for $ {{\mathrm {t}\overline {\mathrm {t}}}} $ and QCD are constrained down by 40 and 14%, respectively. |
| Summary |
| A search for a heavy W' boson decaying to a B or T vector-like quark and a top or b quark, respectively, has been presented. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$ collected in 2016 with the CMS detector at the LHC. The signature considered for both decay modes is a top quark and a Higgs boson, both decaying hadronically, and a b quark jet. Boosted heavy-resonance identification techniques are used to exploit the event signature of three energetic jets and to suppress standard model backgrounds. No significant deviation from the standard model background prediction has been observed. Cross section upper limits on W' boson production in the top quark, Higgs boson, and b quark decay mode are set as a function of the W' mass, for several vector-like quark mass hypotheses. These are the first limits for W' boson production in this decay channel, and cover a range of 0.01 to 0.43 pb in the W' mass range between 1.5 and 4.0 TeV. |
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