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| CMS-B2G-16-023 ; CERN-EP-2017-279 | ||
| Search for ZZ resonances in the $ 2 \ell 2 \nu $ final state in proton-proton collisions at 13 TeV | ||
| CMS Collaboration | ||
| 13 November 2017 | ||
| JHEP 03 (2018) 003 | ||
| Abstract: A search for heavy resonances decaying to a pair of Z bosons is performed using data collected with the CMS detector at the LHC. Events are selected by requiring two oppositely charged leptons (electrons or muons), consistent with the decay of a Z boson, and large missing transverse momentum, which is interpreted as arising from the decay of a second Z boson to two neutrinos. The analysis uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The hypothesis of a spin-2 bulk graviton (X) decaying to a pair of Z bosons is examined for 600 $ \le{m_{\mathrm{X}}} \le $ 2500 GeV and upper limits at 95% confidence level are set on the product of the production cross section and branching fraction of $\mathrm{X}\to \mathrm{Z}\mathrm{Z}$ ranging from 100 to 4 fb. For bulk graviton models characterized by a curvature scale parameter $\tilde{k}= $ 0.5 in the extra dimension, the region ${m_{\mathrm{X}}} < $ 800 GeV is excluded, providing the most stringent limit reported to date. Variations of the model considering the possibility of a wide resonance produced exclusively via gluon-gluon fusion or $\mathrm{q\bar{q}}$ annihilation are also examined. | ||
| Links: e-print arXiv:1711.04370 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Leading order Feynman diagram for the production of a generic resonance X via gluon-gluon fusion decaying to the ZZ final state. |
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Figure 2:
The $ {p_{\mathrm {T}}} ^{\mathrm{Z}}$ distributions for electron (left) and muon (right) channels comparing the data and background model based on control samples in data. The lower panels give the ratio of data to the prediction for the background with only statistical uncertainties shown. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of cross section and branching fraction $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. |
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Figure 2-a:
The $ {p_{\mathrm {T}}} ^{\mathrm{Z}}$ distributions for the electron channel comparing the data and background model based on control samples in data. The lower panel gives the ratio of data to the prediction for the background with only statistical uncertainties shown. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of cross section and branching fraction $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. |
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Figure 2-b:
The $ {p_{\mathrm {T}}} ^{\mathrm{Z}}$ distributions for the muon channel comparing the data and background model based on control samples in data. The lower panel gives the ratio of data to the prediction for the background with only statistical uncertainties shown. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of cross section and branching fraction $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. |
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Figure 3:
The ${{p_{\mathrm {T}}} ^\text {miss}}$ for electron (left) and muon (right) channels comparing the data and background model based on control samples in data. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of cross section and branching fraction $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. The lower panels show the ratio of data to the prediction for the background. The shaded band shows the systematic uncertainties in background, while the statistical uncertainty in the data is shown by the error bars. |
png pdf |
Figure 3-a:
The ${{p_{\mathrm {T}}} ^\text {miss}}$ for the electron channel comparing the data and background model based on control samples in data. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of cross section and branching fraction $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. The lower panel shows the ratio of data to the prediction for the background. The shaded band shows the systematic uncertainties in background, while the statistical uncertainty in the data is shown by the error bars. |
png pdf |
Figure 3-b:
The ${{p_{\mathrm {T}}} ^\text {miss}}$ for the muon channel comparing the data and background model based on control samples in data. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of cross section and branching fraction $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. The lower panel shows the ratio of data to the prediction for the background. The shaded band shows the systematic uncertainties in background, while the statistical uncertainty in the data is shown by the error bars. |
png pdf |
Figure 4:
The $ {m_\mathrm {T}} $ distributions for electron (left) and muon (right) channels comparing the data and background model based on control samples in data, after fitting the background-only model to the data. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of branching fraction and cross section $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. The lower panels show the ratio of data to the prediction for the background. The shaded bands show the systematic uncertainties in the background, while the statistical uncertainty in the data is shown by the error bars. |
png pdf |
Figure 4-a:
The $ {m_\mathrm {T}} $ distributions for the electron muon channel comparing the data and background model based on control samples in data, after fitting the background-only model to the data. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of branching fraction and cross section $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. The lower panel shows the ratio of data to the prediction for the background. The shaded bands show the systematic uncertainties in the background, while the statistical uncertainty in the data is shown by the error bars. |
png pdf |
Figure 4-b:
The $ {m_\mathrm {T}} $ distributions for the electron muon channel comparing the data and background model based on control samples in data, after fitting the background-only model to the data. The expected distribution for a zero width bulk graviton resonance with a mass of 1 TeV is also shown for a value of 1 pb for the product of branching fraction and cross section $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z}) + \mathcal {B} (\mathrm{Z} \mathrm{Z} \to 2\ell 2\nu)$. The lower panel shows the ratio of data to the prediction for the background. The shaded bands show the systematic uncertainties in the background, while the statistical uncertainty in the data is shown by the error bars. |
png pdf |
Figure 5:
Expected and observed limits on the product of cross section and branching fraction of a new spin-2 heavy resonance $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} $, assuming zero width, based on the combined analysis of the electron and muon channels. Expectations for the production cross section $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z})$ are also shown for the benchmark bulk graviton model for three values of the curvature scale parameter $\tilde{k}$. |
png pdf |
Figure 6:
Expected and observed limits on the product of cross section and branching fraction of a new spin-2 bulk heavy resonance $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} $, assuming zero width, shown separately for searches $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} \to \ell \ell \nu \nu $ in the electron (left) and muon (right) final states. The median expected 95% CL limits from the combined analysis (Fig. 5) are also shown. |
png pdf |
Figure 6-a:
Expected and observed limits on the product of cross section and branching fraction of a new spin-2 bulk heavy resonance $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} $, assuming zero width, shown separately for searches $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} \to \ell \ell \nu \nu $ in the electron final state. The median expected 95% CL limits from the combined analysis (Fig. 5) are also shown. |
png pdf |
Figure 6-b:
Expected and observed limits on the product of cross section and branching fraction of a new spin-2 bulk heavy resonance $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} $, assuming zero width, shown separately for searches $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} \to \ell \ell \nu \nu $ in the muon final state. The median expected 95% CL limits from the combined analysis (Fig. 5) are also shown. |
png pdf |
Figure 7:
Expected and observed limits on the product of cross section and branching fraction of a new spin-2 heavy resonance $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} $ based on a combined analysis of the electron and muon channels. The more generic version of the bulk graviton model is considered, assuming either gluon-gluon fusion (left) or ${\mathrm{q} \mathrm{\bar{q}}}$ annihilation (right) processes. Expected limits are also shown for models having various decay widths relative to the mass of the resonance. |
png pdf |
Figure 7-a:
Expected and observed limits on the product of cross section and branching fraction of a new spin-2 heavy resonance $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} $ based on a combined analysis of the electron and muon channels. The more generic version of the bulk graviton model is considered, assuming the gluon-gluon fusion process. Expected limits are also shown for models having various decay widths relative to the mass of the resonance. |
png pdf |
Figure 7-b:
Expected and observed limits on the product of cross section and branching fraction of a new spin-2 heavy resonance $ {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} $ based on a combined analysis of the electron and muon channels. The more generic version of the bulk graviton model is considered, assuming the ${\mathrm{q} \mathrm{\bar{q}}}$ annihilation process. Expected limits are also shown for models having various decay widths relative to the mass of the resonance. |
| Tables | |
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Table 1:
Summary of the normalization uncertainties that are included in the statistical procedure for the electron and muon channels. All values are listed in percentage units and similar categories are grouped for brevity. Sources that do not apply or are found to be negligibly small are marked "--" or "(--),'' respectively. Integrated luminosity and theoretical uncertainties are evaluated separately for effects on normalizations, while all the other uncertainties are considered simultaneously with shape variations in the statistical analysis. Values in the signal column refer to the hypothetical spin-2 bulk graviton signal with a mass of 1 TeV. |
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Table 2:
Event yields for different background contributions and those observed in data in the electron and muon channels. |
| Summary |
| A search for the production of new resonances has been performed in events with a leptonically decaying Z boson and missing transverse momentum, using data corresponding to an integrated luminosity of 35.9 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV. The data are consistent with expectations from standard model processes. The hypothesis of a spin-2 bulk graviton, X, decaying to a pair of Z bosons is examined for 600 $ \le {m_{\mathrm{X}}} \le $ 2500 GeV, and upper limits are set at 95% confidence level on the product of the cross section and branching fraction $\sigma({\mathrm{p}}{\mathrm{p}} \to \mathrm{X}\to \mathrm{Z}\mathrm{Z})$ ranging from 100 to 4 fb. For bulk graviton models characterized by a curvature scale parameter $\tilde{k}= $ 0.5 in the extra dimension, the region ${m_{\mathrm{X}}} < 800$ GeV is excluded, providing the most stringent limit reported to date. The analysis is repeated considering variations of the bulk graviton model to include a large mass-dependent width. Exclusion limits are provided separately for gluon-gluon fusion and $\mathrm{q\bar{q}}$ annihilation production processes. |
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