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| CMS-PAS-B2G-16-001 | ||
| Search for single production of vector-like quarks decaying into final states with a Z boson and a top or a bottom quark | ||
| CMS Collaboration | ||
| July 2016 | ||
| Abstract: A search for the single production of vector-like quarks, $T$ and $B$, decaying into a Z boson and a top or a bottom quark respectively, is presented using data collected by the CMS experiment in proton-proton collisions at $\sqrt{ s } =$ 13 TeV. An additional exotic production mode is studied for the $T$ quark, i.e. the production of a heavy resonance $Z^{\prime}$ with its subsequent decay into $Tt$. The search has been performed in events with a Z boson decaying leptonically, accompanied by a bottom or a top quark decaying hadronically. Observed production cross sections for $T$ and $B$ in the range between 0.97 and 0.13 pb are excluded at 95% confidence level, depending on the resonance mass that ranges from 0.7 to 1.7 TeV, while observed production cross sections for $Z^{\prime}$ are excluded in the range between 0.31 and 0.14 pb, in a mass range between 1.5 and 2.5 TeV. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 05 (2017) 029. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1-a:
Production of a single $T$ and its decay to a Z boson and a t quark. |
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Figure 1-b:
Production of a single $B$ and its decay to a Z boson and a b quark. |
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Figure 2-a:
Comparison between data and simulation for the reconstructed top mass in the four $T$ categories, after preselection only. No cuts on $\Delta R(lep1,lep2)$, number of b-jets and ${p_{\mathrm {T}}}$ of the leading muon are applied. |
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Figure 2-b:
Comparison between data and simulation for the reconstructed top mass in the four $T$ categories, after preselection only. No cuts on $\Delta R(lep1,lep2)$, number of b-jets and ${p_{\mathrm {T}}}$ of the leading muon are applied. |
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Figure 2-c:
Comparison between data and simulation for the reconstructed top mass in the four $T$ categories, after preselection only. No cuts on $\Delta R(lep1,lep2)$, number of b-jets and ${p_{\mathrm {T}}}$ of the leading muon are applied. |
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Figure 2-d:
Comparison between data and simulation for the reconstructed top mass in the four $T$ categories, after preselection only. No cuts on $\Delta R(lep1,lep2)$, number of b-jets and ${p_{\mathrm {T}}}$ of the leading muon are applied. |
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Figure 3-a:
Comparison between data and simulation for the $b$ quark ${p_{\mathrm {T}}}$ in the two $B$ categories, after preselection only. No cuts on $\Delta R(lep1,lep2)$, number of b-jets and ${p_{\mathrm {T}}}$ of the leading muon are applied. |
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Figure 3-b:
Comparison between data and simulation for the $b$ quark ${p_{\mathrm {T}}}$ in the two $B$ categories, after preselection only. No cuts on $\Delta R(lep1,lep2)$, number of b-jets and ${p_{\mathrm {T}}}$ of the leading muon are applied. |
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Figure 4-a:
Number of events in the control region $N_{cr}(M_{T/B})$ for the fully merged region (a), partially merged region (b), resolved region (c,d) and events with a Z boson and a b-jet (e,f), for events with a Z boson decaying into muons (c,e) and electrons (d,f). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. |
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Figure 4-b:
Number of events in the control region $N_{cr}(M_{T/B})$ for the fully merged region (a), partially merged region (b), resolved region (c,d) and events with a Z boson and a b-jet (e,f), for events with a Z boson decaying into muons (c,e) and electrons (d,f). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. |
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Figure 4-c:
Number of events in the control region $N_{cr}(M_{T/B})$ for the fully merged region (a), partially merged region (b), resolved region (c,d) and events with a Z boson and a b-jet (e,f), for events with a Z boson decaying into muons (c,e) and electrons (d,f). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. |
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Figure 4-d:
Number of events in the control region $N_{cr}(M_{T/B})$ for the fully merged region (a), partially merged region (b), resolved region (c,d) and events with a Z boson and a b-jet (e,f), for events with a Z boson decaying into muons (c,e) and electrons (d,f). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. |
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Figure 4-e:
Number of events in the control region $N_{cr}(M_{T/B})$ for the fully merged region (a), partially merged region (b), resolved region (c,d) and events with a Z boson and a b-jet (e,f), for events with a Z boson decaying into muons (c,e) and electrons (d,f). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. |
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Figure 4-f:
Number of events in the control region $N_{cr}(M_{T/B})$ for the fully merged region (a), partially merged region (b), resolved region (c,d) and events with a Z boson and a b-jet (e,f), for events with a Z boson decaying into muons (c,e) and electrons (d,f). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. |
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Figure 5-a:
Comparison between the background estimated with the alpha method and observed data for the $T$ categories: fully merged region (a), partially merged region (b), and resolved region (c,d) for events with a Z boson decaying into muons (c) and electrons (d). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. The uncertainties on the background estimation method include both statistical and systematic errors, as described in section 7. |
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Figure 5-b:
Comparison between the background estimated with the alpha method and observed data for the $T$ categories: fully merged region (a), partially merged region (b), and resolved region (c,d) for events with a Z boson decaying into muons (c) and electrons (d). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. The uncertainties on the background estimation method include both statistical and systematic errors, as described in section 7. |
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Figure 5-c:
Comparison between the background estimated with the alpha method and observed data for the $T$ categories: fully merged region (a), partially merged region (b), and resolved region (c,d) for events with a Z boson decaying into muons (c) and electrons (d). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. The uncertainties on the background estimation method include both statistical and systematic errors, as described in section 7. |
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Figure 5-d:
Comparison between the background estimated with the alpha method and observed data for the $T$ categories: fully merged region (a), partially merged region (b), and resolved region (c,d) for events with a Z boson decaying into muons (c) and electrons (d). For the fully merged region and the partially merged region, events with Z to muons and events with Z to electrons are taken together. For the fully merged region, no shape analysis is performed due to reduced statistics so one single bin is shown. The uncertainties on the background estimation method include both statistical and systematic errors, as described in section 7. |
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Figure 6-a:
Comparison between the background estimated with the alpha method and observed data for the $B$ categories: events with $Z$ to muons (a) and to electrons (b). The uncertainties on the background estimation method include both statistical and systematic errors, as described in section 7. |
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Figure 6-b:
Comparison between the background estimated with the alpha method and observed data for the $B$ categories: events with $Z$ to muons (a) and to electrons (b). The uncertainties on the background estimation method include both statistical and systematic errors, as described in section 7. |
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Figure 7-a:
Observed and expected upper limit on the $\sigma \cdot BR$ for the singlet LH $Tb$ (a) and doublet RH $Tt$ (b) production mode. |
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Figure 7-b:
Observed and expected upper limit on the $\sigma \cdot BR$ for the singlet LH $Tb$ (a) and doublet RH $Tt$ (b) production mode. |
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Figure 8-a:
Observed and expected upper limit on the $\sigma \cdot BR$ for the $Bt$ (a) and $Bb$ (b) signal in the singlet LH scenario. |
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Figure 8-b:
Observed and expected upper limit on the $\sigma \cdot BR$ for the $Bt$ (a) and $Bb$ (b) signal in the singlet LH scenario. |
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Figure 9-a:
Exclusion region in the plane defined by: (a) the mass of the $T$ resonance and the coupling $C(bW)$ for LH $Tb$ production mode, under the assumption that the $T$ is a singlet; (b) the mass of the $T$ resonance and the coupling $C(tZ)$ for the RH scenario, considering $Tt$ production mode, under the assumption that $T$ is a doublet and that $BR(T\rightarrow tZ) = BR(T\rightarrow tH) = $ 0.5 ; (c) the mass of the $B$ resonance and the coupling $C(tW)$ for the LH signal; in this case $Bt$ and $Bb$ production modes are combined together, under the assumption that $C(bW) = \sqrt {2}\cdot C(tZ)$. |
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Figure 9-b:
Exclusion region in the plane defined by: (a) the mass of the $T$ resonance and the coupling $C(bW)$ for LH $Tb$ production mode, under the assumption that the $T$ is a singlet; (b) the mass of the $T$ resonance and the coupling $C(tZ)$ for the RH scenario, considering $Tt$ production mode, under the assumption that $T$ is a doublet and that $BR(T\rightarrow tZ) = BR(T\rightarrow tH) = $ 0.5 ; (c) the mass of the $B$ resonance and the coupling $C(tW)$ for the LH signal; in this case $Bt$ and $Bb$ production modes are combined together, under the assumption that $C(bW) = \sqrt {2}\cdot C(tZ)$. |
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Figure 9-c:
Exclusion region in the plane defined by: (a) the mass of the $T$ resonance and the coupling $C(bW)$ for LH $Tb$ production mode, under the assumption that the $T$ is a singlet; (b) the mass of the $T$ resonance and the coupling $C(tZ)$ for the RH scenario, considering $Tt$ production mode, under the assumption that $T$ is a doublet and that $BR(T\rightarrow tZ) = BR(T\rightarrow tH) = $ 0.5 ; (c) the mass of the $B$ resonance and the coupling $C(tW)$ for the LH signal; in this case $Bt$ and $Bb$ production modes are combined together, under the assumption that $C(bW) = \sqrt {2}\cdot C(tZ)$. |
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Figure 10:
Observed and expected upper limit on the $\sigma \cdot BR$ for the $Z^{\prime } \rightarrow Tt$ signal. It has been considered a 100% branching ratio (BR) of $T$ in $tZ$ final state. In order to consider different BR, the limits have to be scaled by the corresponding BR. |
| Tables | |
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Table 1:
Theoretical cross sections for $Tb$, $Bt$, $Bb$ and $Tt$ processes for the different mass points considered in the analysis for unitary couplings. |
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Table 2:
Event yields for background events estimated with the data-driven method and observed data. The quoted uncertainties on the background estimation from data-driven prediction include both statistical and systematic errors, as described in section 7. Expected signal yields are also shown for three example mass points. |
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Table 3:
Summary of the systematics applied in the analysis. |
| Summary |
| A search for the single production of vector-like quarks, $T$ and $B$, has been presented. This is the first search looking for this signal performed by CMS in events with a Z boson decaying leptonically, and a bottom or a top quark decaying hadronically. Observed limits on the production cross sections for a LH $Tb$ in the range between 0.97 and 0.16 pb are set at 95% confidence level, depending on the resonance mass that ranges from 0.7 to 1.7 TeV and between 0.60 and 0.14 pb for RH $Tt$ signal. For LH $B$ produced in association with a top quark, cross sections in a range between 0.68 and 0.17 pb are excluded in the same mass range, while for $B$ produced in association with a b quark, cross section in a range between 1.27 and 0.30 pb are excluded. Finally production cross sections of a $T$ quark from the decay of a $Z^{\prime} \rightarrow Tt$ are excluded in the range between 0.31 and 0.14 pb, depending on the $Z^{\prime}$ mass between 1.5 and 2.5 TeV. |
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