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| CMS-PAS-B2G-17-005 | ||
| Search for heavy resonances decaying into a Z boson and a vector boson in the $\nu \nu \mathrm{q\bar{q}}$ final state | ||
| CMS Collaboration | ||
| July 2017 | ||
| Abstract: A search is presented for heavy resonances decaying into a Z boson and either a W boson or another Z boson (WZ or ZZ), with one Z boson decaying into a pair of neutrinos and the other boson decaying hadronically into a pair of collimated quarks, which is reconstructed as a highly energetic boosted jet. The search is performed using the data collected by the CMS detector at the CERN LHC during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 35.9 fb$^{-1}$. No excess is observed in data with regards to background expectations. Results are interpreted in beyond standard model scenarios. Limits on production cross sections are set in the range 0.8-50 fb for spin-2 bulk gravitons and for W' bosons in the context of the heavy vector triplet (HVT) model. For the two HVT scenarios considered, a W' resonance is excluded at 95% CL up to a mass of 3.2 TeV in the first case and 3.5 TeV in the second. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 07 (2018) 075. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Comparison of data and simulated events in the sideband regions. Left: the corrected mass of the leading AK8 jet, interpreted as the hadronically decaying vector boson. The background processes predicted by the SM are depicted as colored filled histograms. The Z+jets $\rightarrow $ $\nu \nu $ contribution is shown in light blue. The W+jets $\rightarrow $ $\ell \nu $ events are displayed in violet. Secondary backgrounds arise from events with a single top quark (dark yellow), a $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ pair (light yellow), and two vector bosons (blue). Two possible signal hypotheses are shown (with a cross section of 10 pb): a spin-1 $ \mathrm{ W^{+} }' $ with mass 3 TeV (light red) and a spin-2 bulk graviton with mass 1 TeV (light green). The signal distributions are displayed over the whole jet mass spectrum, not restricted to sidebands. The data points are shown by the black markers, along with their associated statistical uncertainties. Right: the distribution of the $\tau _{21}$ subjettiness of the vector boson candidate, which is used to define low- and high-purity categories. The dividing point between the two categories is set at $\tau _{21}= $ 0.35. |
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Figure 1-a:
The corrected mass of the leading AK8 jet, interpreted as the hadronically decaying vector boson. The background processes predicted by the SM are depicted as colored filled histograms. The Z+jets $\rightarrow $ $\nu \nu $ contribution is shown in light blue. The W+jets $\rightarrow $ $\ell \nu $ events are displayed in violet. Secondary backgrounds arise from events with a single top quark (dark yellow), a $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $ pair (light yellow), and two vector bosons (blue). Two possible signal hypotheses are shown (with a cross section of 10 pb): a spin-1 $ \mathrm{ W^{+} }' $ with mass 3 TeV (light red) and a spin-2 bulk graviton with mass 1 TeV (light green). The signal distributions are displayed over the whole jet mass spectrum, not restricted to sidebands. The data points are shown by the black markers, along with their associated statistical uncertainties. |
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Figure 1-b:
The distribution of the $\tau _{21}$ subjettiness of the vector boson candidate, which is used to define low- and high-purity categories. The dividing point between the two categories is set at $\tau _{21}= $ 0.35. |
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Figure 2:
Background yield prediction in the signal region obtained with the $\alpha $ method, in the low-purity (left ) and high-purity category (right ). Background processes predicted by the SM are depicted as colored histograms. The main contribution (light blue) consists of events where a vector boson is produced in association with a hadronic jet. The secondary backgrounds (events with a top quark, in yellow, and events with diboson production, in blue) are completely predicted from simulation. The dotted vertical lines define the different jet mass regions: the sideband regions (low sideband, LSB, and high sideband, HSB), where the fit to data is performed; the signal region (SR), where the $\alpha $ method prediction is compared to data; and the Higgs region, which is excluded from the analysis. The bottom panels show the fit pulls for each bin; i.e. , the number of events observed in data minus the number of events predicted by the fit, divided by the uncertainty in the data. We observe that the data (black markers, along with their Poissonian uncertainties) are in agreement with the predictions. |
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Figure 2-a:
Background yield prediction in the signal region obtained with the $\alpha $ method, in the low-purity category. Background processes predicted by the SM are depicted as colored histograms. The main contribution (light blue) consists of events where a vector boson is produced in association with a hadronic jet. The secondary backgrounds (events with a top quark, in yellow, and events with diboson production, in blue) are completely predicted from simulation. The dotted vertical lines define the different jet mass regions: the sideband regions (low sideband, LSB, and high sideband, HSB), where the fit to data is performed; the signal region (SR), where the $\alpha $ method prediction is compared to data; and the Higgs region, which is excluded from the analysis. The bottom panels show the fit pulls for each bin; i.e. , the number of events observed in data minus the number of events predicted by the fit, divided by the uncertainty in the data. We observe that the data (black markers, along with their Poissonian uncertainties) are in agreement with the predictions. |
png pdf |
Figure 2-b:
Background yield prediction in the signal region obtained with the $\alpha $ method, in the high-purity category. Background processes predicted by the SM are depicted as colored histograms. The main contribution (light blue) consists of events where a vector boson is produced in association with a hadronic jet. The secondary backgrounds (events with a top quark, in yellow, and events with diboson production, in blue) are completely predicted from simulation. The dotted vertical lines define the different jet mass regions: the sideband regions (low sideband, LSB, and high sideband, HSB), where the fit to data is performed; the signal region (SR), where the $\alpha $ method prediction is compared to data; and the Higgs region, which is excluded from the analysis. The bottom panels show the fit pulls for each bin; i.e. , the number of events observed in data minus the number of events predicted by the fit, divided by the uncertainty in the data. We observe that the data (black markers, along with their Poissonian uncertainties) are in agreement with the predictions. |
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Figure 3:
Expected background shapes as a function of the transverse mass of the diboson candidate obtained using the $\alpha $ method in the low-purity (left ) and high-purity category (right ), represented as colored histograms (light blue: vector boson in association with jets; yellow: processes involving a top quark; blue: diboson production). As a reference, the expected distribution of a $ \mathrm{ W^{+} }' $ with a mass of 3 TeV and cross section of 10 fb decaying into two Z bosons is displayed. The data (black markers) are in agreement with the predictions. |
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Figure 3-a:
Expected background shapes as a function of the transverse mass of the diboson candidate obtained using the $\alpha $ method in the low-purity category, represented as colored histograms (light blue: vector boson in association with jets; yellow: processes involving a top quark; blue: diboson production). As a reference, the expected distribution of a $ \mathrm{ W^{+} }' $ with a mass of 3 TeV and cross section of 10 fb decaying into two Z bosons is displayed. The data (black markers) are in agreement with the predictions. |
png pdf |
Figure 3-b:
Expected background shapes as a function of the transverse mass of the diboson candidate obtained using the $\alpha $ method in the high-purity category, represented as colored histograms (light blue: vector boson in association with jets; yellow: processes involving a top quark; blue: diboson production). As a reference, the expected distribution of a $ \mathrm{ W^{+} }' $ with a mass of 3 TeV and cross section of 10 fb decaying into two Z bosons is displayed. The data (black markers) are in agreement with the predictions. |
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Figure 4:
The observed and expected limits, with 68% and 95% uncertainty bands, on the product of the cross section and branching fraction $\sigma \mathcal {B} ( \mathrm{ W^{+} }' \rightarrow \mathrm{ W } _{\text {had}} {\mathrm{ Z } } _{\text {inv}})$ for a spin-1 HVT signal hypothesis, as a function of the reconstructed transverse mass of the diboson resonance. The low- and high-purity categories have been combined. The colored lines show the theoretical predictions for the two HVT models considered, model A (blue) and model B (red). The background shape is predicted with the $\alpha $ ratio method. |
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Figure 5:
The observed and expected limits, with 68% and 95% uncertainty bands, on the product of the cross section and branching fraction $\sigma \mathcal {B} (G \rightarrow {\mathrm{ Z } } _{\text {had}} {\mathrm{ Z } } _{\text {inv}})$ for a spin-2 bulk graviton signal hypothesis, as a function of the reconstructed transverse mass of the diboson resonance. The low- and high-purity categories have been combined. The colored lines show the theoretical predictions for two different curvature parameters, $\tilde{k}=$ 1.0 (red) and $\tilde{k}=$ 0.5 (blue). The background shape is predicted with the $\alpha $ ratio method. |
| Summary |
| This paper presents a search for heavy diboson resonances in the decay mode $\mathrm{ Z } \rightarrow \nu\nu$ and $\mathrm{ W }/\mathrm{ Z } \rightarrow \mathrm{ q }\mathrm{ \bar{q} }$. The hadronically decaying W or Z boson is reconstructed as a large-cone jet. The invisible decay of the Z boson manifests as a large amount of missing transverse momentum recoiling against the jet. The final transverse components of the VZ resonance momentum are used to define the transverse mass variable, where a search for a localized excess is performed. The expected background is described with a hybrid data-simulation approach that takes advantage of data sidebands to predict the background normalization and shape in the signal region. To improve the discovery potential, two purity categories are defined, based on jet substructure observables. An unbinned maximum likelihood fit is performed. No excesses are observed in data compared to standard model predictions. The 95% CL limit is established for the product of the cross section and branching fraction for a spin-2 bulk graviton and spin-1 heavy vector triplet (HVT) $ \mathrm{ W^{+} }' $ in a range between 0.8 and 50 fb, depending on the resonance mass. The $ \mathrm{ W^{+} }' $ described in HVT model A is excluded up to a mass of 3.2 TeV at 95% CL, and up to 3.5 TeV in HVT model B. The limits on HVT models are significantly improved (by one order of magnitude in the cross section and almost 1 TeV in the upper limit of the resonance mass) with regards to previous searches performed in the same final state by the ATLAS collaboration [42] and in the $\ell \ell \mathrm{ q }\mathrm{ \bar{q} }$ final state by the CMS collaboration [43,44]. |
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Compact Muon Solenoid LHC, CERN |
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