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| CMS-PAS-B2G-16-022 | ||
| Search for heavy resonances decaying into a Z boson and a W boson in the $\ell^+\ell^-\mathrm{q}\bar{\mathrm{q}}$ final state | ||
| CMS Collaboration | ||
| January 2017 | ||
| Abstract: A search for heavy resonances decaying into a pair of vector bosons is performed in the $ 2\ell 2\mathrm{q} $ final state using 12.9 fb$^{-1}$ of data collected in 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of $\sqrt{s}= $ 13 TeV. The final state probed involves the leptonic decay of a Z boson ($\mathrm{Z} \to \ell \ell$, with $\ell = \mathrm{e},\mu$), while the other vector boson W is reconstructed from high-momentum quark pairs detected as a single massive jet. The discriminating power of the jet mass distribution and jet substructure are exploited to suppress the amount of background from known standard model processes. The search is performed in the boosted regime for resonances with mass larger than 600 GeV up to 3000 GeV. The result is consistent with the standard model prediction and upper limits on the production cross section for spin-1 resonances are derived as a function of the resonance mass. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Transverse momentum of the Z boson candidate (left) and AK8 jet (right) selected in the analysis. Only events with jet mass greater than 30 GeV are shown. The shaded area represents the statistical uncertainty on the simulated samples. The ratio of data over simulation is reported at the bottom of each panel. A W' signal model hypothesis, magnified by a factor 10, is also shown. |
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Figure 1-a:
Transverse momentum of the Z boson candidateselected in the analysis. Only events with jet mass greater than 30 GeV are shown. The shaded area represents the statistical uncertainty on the simulated samples. The ratio of data over simulation is reported at the bottom of each panel. A W' signal model hypothesis, magnified by a factor 10, is also shown. |
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Figure 1-b:
Transverse momentum of AK8 jet selected in the analysis. Only events with jet mass greater than 30 GeV are shown. The shaded area represents the statistical uncertainty on the simulated samples. The ratio of data over simulation is reported at the bottom of each panel. A W' signal model hypothesis, magnified by a factor 10, is also shown. |
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Figure 2:
The $\tau _{21}$ of the AK8 jet selected in the electron (left) and muon (right) categories. Only events with jet mass greater than 30 GeV are shown. The shaded area represents the statistical uncertainty on the simulated samples. The ratio of data over simulation is reported at the bottom of each panel. A W' signal model hypothesis, magnified by a factor 10, is also shown. |
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Figure 2-a:
The $\tau _{21}$ of the AK8 jet selected in the electron category. Only events with jet mass greater than 30 GeV are shown. The shaded area represents the statistical uncertainty on the simulated samples. The ratio of data over simulation is reported at the bottom of each panel. A W' signal model hypothesis, magnified by a factor 10, is also shown. |
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Figure 2-b:
The $\tau _{21}$ of the AK8 jet selected in the muon category. Only events with jet mass greater than 30 GeV are shown. The shaded area represents the statistical uncertainty on the simulated samples. The ratio of data over simulation is reported at the bottom of each panel. A W' signal model hypothesis, magnified by a factor 10, is also shown. |
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Figure 3:
Signal efficiency for a W' signal model, separated by final state and purity category. The efficiency is evaluated as the fraction of generated signal events decaying in the $\ell \ell $qq final state (with $\ell = e, \mu $ depending on the considered leptonic category) passing the event selections described in Section. |
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Figure 4:
Functional forms modeling the ${m_\text {j}}$ distributions extracted from a fit to data (Z+jets) or derived from simulation (Top and VV) in the electron (top) and muon (bottom) channels, for the high (left) and low (right) purity categories. The shaded area represents the Z+jets distribution uncertainty. The bottom panels report the pulls distribution between data and SM background expectation $(N^{data}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 4-a:
Functional forms modeling the ${m_\text {j}}$ distributions extracted from a fit to data (Z+jets) or derived from simulation (Top and VV) in the electron muon channel, for the high purity category. The shaded area represents the Z+jets distribution uncertainty. The bottom panel reports the pulls distribution between data and SM background expectation $(N^{data}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 4-b:
Functional forms modeling the ${m_\text {j}}$ distributions extracted from a fit to data (Z+jets) or derived from simulation (Top and VV) in the electron channel, for the low purity category. The shaded area represents the Z+jets distribution uncertainty. The bottom panel reports the pulls distribution between data and SM background expectation $(N^{data}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 4-c:
Functional forms modeling the ${m_\text {j}}$ distributions extracted from a fit to data (Z+jets) or derived from simulation (Top and VV) in the muon channel, for the high purity category. The shaded area represents the Z+jets distribution uncertainty. The bottom panel reports the pulls distribution between data and SM background expectation $(N^{data}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 4-d:
Functional forms modeling the ${m_\text {j}}$ distributions extracted from a fit to data (Z+jets) or derived from simulation (Top and VV) in the muon channel, for the low purity category. The shaded area represents the Z+jets distribution uncertainty. The bottom panel reports the pulls distribution between data and SM background expectation $(N^{data}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 5:
Expected and observed events on the resonance candidate mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ distributions in the electron (top) and muon (bottom) channels, and separately for the high (left) and low purity (right) categories. The shaded area represents the shape uncertainty on the Z+jets background. The bottom panels report the pulls distribution between data and SM background expectation $(N^{obs}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 5-a:
Expected and observed events on the resonance candidate mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ distributions in the electron channel, and separately for the high purity category. The shaded area represents the shape uncertainty on the Z+jets background. The bottom panels report the pulls distribution between data and SM background expectation $(N^{obs}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 5-b:
Expected and observed events on the resonance candidate mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ distributions in the electron channel, and separately for the low purity category. The shaded area represents the shape uncertainty on the Z+jets background. The bottom panels report the pulls distribution between data and SM background expectation $(N^{obs}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 5-c:
Expected and observed events on the resonance candidate mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ distributions in the muon channel, and separately for the high purity category. The shaded area represents the shape uncertainty on the Z+jets background. The bottom panels report the pulls distribution between data and SM background expectation $(N^{obs}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 5-d:
Expected and observed events on the resonance candidate mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ distributions in the muon channel, and separately for the low purity category. The shaded area represents the shape uncertainty on the Z+jets background. The bottom panels report the pulls distribution between data and SM background expectation $(N^{obs}-N^{bkg})/\sigma $, where $\sigma $ is the normalized Poisson error on the data. |
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Figure 6:
Reconstructed signal mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ for different generated mass ${m_{ {\mathrm {X}} }}$ hypotheses of a W' signal, modeled with a Crystal Ball function, and separately by final state: electron (top) and muon (bottom) channels, and separately for the high (left) and low purity (right) categories. The distributions are normalized to unit area. |
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Figure 6-a:
Reconstructed signal mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ for different generated mass ${m_{ {\mathrm {X}} }}$ hypotheses of a W' signal, modeled with a Crystal Ball function, and separately by final state: electron channel, and separately for the high purity category. The distributions are normalized to unit area. |
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Figure 6-b:
Reconstructed signal mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ for different generated mass ${m_{ {\mathrm {X}} }}$ hypotheses of a W' signal, modeled with a Crystal Ball function, and separately by final state: electron channel, and separately for the low purity category. The distributions are normalized to unit area. |
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Figure 6-c:
Reconstructed signal mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ for different generated mass ${m_{ {\mathrm {X}} }}$ hypotheses of a W' signal, modeled with a Crystal Ball function, and separately by final state: muon channel, and separately for the high purity category. The distributions are normalized to unit area. |
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Figure 6-d:
Reconstructed signal mass ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ for different generated mass ${m_{ {\mathrm {X}} }}$ hypotheses of a W' signal, modeled with a Crystal Ball function, and separately by final state: muon channel, and separately for the low purity category. The distributions are normalized to unit area. |
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Figure 7:
Observed and expected 95% CL upper limit on $\sigma _{ \mathrm{W}'} \times {\mathcal {B}}(\mathrm{W}'\to {\mathrm{ Z } } {\mathrm {W}})$ as a function of the resonance mass for a narrow spin-1 resonance , including all statistical and systematic uncertainties. The electron and muon channels and high and low purity categories are combined together. The green and yellow bands are the ${\pm }1$ and ${\pm }$2 standard deviation uncertainty bands on the expected limit. Theoretical predictions for W' produced in the framework of HVT model A and model B are also shown. |
| Tables | |
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Table 1:
Expected and observed number of events in the SR (65 $< {m_\text {j}} <$ 105 GeV). The uncertainties originating from the fit and the top and diboson ${m_\text {j}}$ distributions are reported separately, as well as the difference in normalization between the nominal and the alternative function choice. |
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Table 2:
Summary of systematic uncertainties for backgrounds and signal samples. The uncertainty sources propagated to the ${m_{ { {\mathrm {V}} {\mathrm{ Z } } } }}$ shape are marked with a tick. In the case a systematic uncertainty depends in the resonance mass (for signal) or on the category (for background), the extreme values are reported in the table. |
| Summary |
| This article describes a search for a heavy resonance with mass between 600 GeV and 3 TeV, decaying into a Z boson and a W boson. The data collected at $ \sqrt{s} = $ 13 TeV during the 2016 operations by the CMS experiment at LHC Run-2 are analyzed. The data set size corresponds to an integrated luminosity of 12.9 fb$^{-1}$. The final state explored consists in the leptonic decays of the Z boson into an electron or muon pair, and the decay of the W boson into a pair of collimated quarks. Depending on the resonance mass, upper limits of 12-370 fb are set on the cross section of a spin-1 HVT W' signal multiplied by the ZW branching ratio. The results of the present analysis do not confirm the mild excess consistent with a mass hypothesis of 650 GeV observed by the CMS collaboration [56], and are comparable with the most recent results of the ATLAS collaboration [57]. |
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