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CMS-PAS-HIG-17-012
Search for a new scalar resonance decaying to a pair of Z bosons in proton-proton collisions at $\sqrt {s} = $ 13 TeV
Abstract: A search for a new scalar resonance decaying to a pair of Z bosons is performed in the mass range from 130 GeV to 3 TeV and for various width scenarios. The analysis is based on proton-proton collisions recorded by the CMS experiment at the CERN LHC in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$ at a center-of-mass energy of 13 TeV. Z boson pair decays are reconstructed using the $ 4 \ell $, $ 2 \ell 2 \mathrm{q} $, and $ 2 \ell 2 \nu $ final states, where $\ell = \mathrm{e}$ or $\mu$. Both gluon fusion and electroweak production of the scalar resonance are considered, with a free parameter describing their relative cross sections. A dedicated categorization of events, based on the kinematic properties of associated jets, and matrix-element techniques are employed for an optimal signal-to-background separation. Description of the interference between signal and background amplitudes for a resonance of an arbitrary width is included. No significant excess of events is observed and limits are set on the production cross section for a new scalar boson for a large range of masses and widths.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Illustration of an X boson production from ggH, $\mathrm{g} \mathrm{g} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} \to (\ell ^+\ell ^-)(f\bar{f})$ (left) and VBF $\mathrm{q} {\mathrm{q} ^\prime}\to \mathrm{q} {\mathrm{q} ^\prime} {\mathrm {X}} \to \mathrm{q} {\mathrm{q} ^\prime}\mathrm{Z} \mathrm{Z} $ (right).

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Figure 1-a:
Illustration of an X boson production from ggH, $\mathrm{g} \mathrm{g} \to {\mathrm {X}} \to \mathrm{Z} \mathrm{Z} \to (\ell ^+\ell ^-)(f\bar{f})$.

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Figure 1-b:
Illustration of an X boson production from VBF $\mathrm{q} {\mathrm{q} ^\prime}\to \mathrm{q} {\mathrm{q} ^\prime} {\mathrm {X}} \to \mathrm{q} {\mathrm{q} ^\prime}\mathrm{Z} \mathrm{Z} $.

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Figure 2:
Distribution of the four-leptons invariant mass in untagged (upper left), VBF-tagged (upper right) and RSE (bottom left) category and of ${\cal D}_{\rm bkg}^{\rm kin}$ for all selected events (bottom right). Signal expectations including the interference effect for several mass and width hypotheses are shown. The cross section for the signal corresponds to the expected exclusion value (times a scaling indicated on the panel to make them more visible), and is normalized to a total of 400 events in the bottom right panel.

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Figure 2-a:
Distribution of the four-leptons invariant mass in the untagged category. Signal expectations including the interference effect for several mass and width hypotheses are shown. The cross section for the signal corresponds to the expected exclusion value (times a scaling indicated on the panel to make them more visible).

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Figure 2-b:
Distribution of the four-leptons invariant mass in the VBF-tagged category. Signal expectations including the interference effect for several mass and width hypotheses are shown. The cross section for the signal corresponds to the expected exclusion value (times a scaling indicated on the panel to make them more visible).

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Figure 2-c:
Distribution of the four-leptons invariant mass in the RSE category. Signal expectations including the interference effect for several mass and width hypotheses are shown. The cross section for the signal corresponds to the expected exclusion value (times a scaling indicated on the panel to make them more visible).

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Figure 2-d:
Distribution of ${\cal D}_{\rm bkg}^{\rm kin}$ for all selected events. Signal expectations including the interference effect for several mass and width hypotheses are shown. The cross section for the signal is normalized to a total of 400 events.

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Figure 3:
Distribution of the invariant mass $ {m_{{\mathrm{Z}} {\mathrm{Z}}}} $ in the signal region for the merged (left) and resolved (right) case for the different categories in the $ 2 \ell 2 \mathrm{q} $ channel. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal. The blue hatched bands refer to the sum of MC- and data-derived background estimations as described in the text. Lower panels show the relative difference between data and background estimation in each case.

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Figure 3-a:
Distribution of the invariant mass $ {m_{{\mathrm{Z}} {\mathrm{Z}}}} $ in the signal region for the merged case for the untagged category in the $ 2 \ell 2 \mathrm{q} $ channel. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal. The blue hatched bands refer to the sum of MC- and data-derived background estimations as described in the text. The lower panel shows the relative difference between data and background estimation in each case.

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Figure 3-b:
Distribution of the invariant mass $ {m_{{\mathrm{Z}} {\mathrm{Z}}}} $ in the signal region for the resolved case for the untagged category in the $ 2 \ell 2 \mathrm{q} $ channel. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal. The blue hatched bands refer to the sum of MC- and data-derived background estimations as described in the text. The lower panel shows the relative difference between data and background estimation in each case.

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Figure 3-c:
Distribution of the invariant mass $ {m_{{\mathrm{Z}} {\mathrm{Z}}}} $ in the signal region for the merged case for the VBF-tagged category in the $ 2 \ell 2 \mathrm{q} $ channel. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal. The blue hatched bands refer to the sum of MC- and data-derived background estimations as described in the text. The lower panel shows the relative difference between data and background estimation in each case.

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Figure 3-d:
Distribution of the invariant mass $ {m_{{\mathrm{Z}} {\mathrm{Z}}}} $ in the signal region for the resolved case for the VBF-tagged category in the $ 2 \ell 2 \mathrm{q} $ channel. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal. The blue hatched bands refer to the sum of MC- and data-derived background estimations as described in the text. The lower panel shows the relative difference between data and background estimation in each case.

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Figure 3-e:
Distribution of the invariant mass $ {m_{{\mathrm{Z}} {\mathrm{Z}}}} $ in the signal region for the merged case for the b-tagged category in the $ 2 \ell 2 \mathrm{q} $ channel. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal. The blue hatched bands refer to the sum of MC- and data-derived background estimations as described in the text. The lower panel shows the relative difference between data and background estimation in each case.

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Figure 3-f:
Distribution of the invariant mass $ {m_{{\mathrm{Z}} {\mathrm{Z}}}} $ in the signal region for the resolved case for the b-tagged category in the $ 2 \ell 2 \mathrm{q} $ channel. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal. The blue hatched bands refer to the sum of MC- and data-derived background estimations as described in the text. The lower panel shows the relative difference between data and background estimation in each case.

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Figure 4:
Distribution of the discriminant ${\mathcal {D}_\textrm {bkg}^\textrm {Zjj}} $ (left) and $ {\mathcal {D}_\textrm {2jet}^\textrm {VBF}} $ (right) in the signal region for the resolved selection. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal.

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Figure 4-a:
Distribution of the discriminant ${\mathcal {D}_\textrm {bkg}^\textrm {Zjj}} $ in the signal region for the resolved selection. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal.

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Figure 4-b:
Distribution of $ {\mathcal {D}_\textrm {2jet}^\textrm {VBF}} $ in the signal region for the resolved selection. The points represent the data, the stacked histograms the expected background from simulation, and the open histograms the expected signal.

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Figure 5:
Distribution of the transverse mass $m_{\mathrm{T}}$ in the signal region for the different analysis categories for the $ 2 \ell 2 \nu $ channel, in the ee (left) and $\mu \mu $ final states (right). The points represent the data and the stacked histograms the expected background. The open histograms show the expected gluon-fusion and VBF signals for cross sections times branching fraction $\sigma (\rm p\rm p \to \rm H \to {\mathrm{Z}} {\mathrm{Z}})=$ 50 fb. Lower panels show the ratio of data to the expected background. The shaded areas show the systematic and total statistical plus systematic uncertainties in the background estimation.

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Figure 5-a:
Distribution of the transverse mass $m_{\mathrm{T}}$ in the signal region for the 0-jet category for the $ 2 \ell 2 \nu $ channel, in the ee final state. The points represent the data and the stacked histograms the expected background. The open histograms show the expected gluon-fusion and VBF signals for cross sections times branching fraction $\sigma (\rm p\rm p \to \rm H \to {\mathrm{Z}} {\mathrm{Z}})=$ 50 fb. Lower panels show the ratio of data to the expected background. The shaded areas show the systematic and total statistical plus systematic uncertainties in the background estimation.

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Figure 5-b:
Distribution of the transverse mass $m_{\mathrm{T}}$ in the signal region for the 0-jet category for the $ 2 \ell 2 \nu $ channel, in the $\mu \mu $ final state. The points represent the data and the stacked histograms the expected background. The open histograms show the expected gluon-fusion and VBF signals for cross sections times branching fraction $\sigma (\rm p\rm p \to \rm H \to {\mathrm{Z}} {\mathrm{Z}})=$ 50 fb. Lower panels show the ratio of data to the expected background. The shaded areas show the systematic and total statistical plus systematic uncertainties in the background estimation.

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Figure 5-c:
Distribution of the transverse mass $m_{\mathrm{T}}$ in the signal region for the $\geq$ 1-jet category for the $ 2 \ell 2 \nu $ channel, in the ee final state. The points represent the data and the stacked histograms the expected background. The open histograms show the expected gluon-fusion and VBF signals for cross sections times branching fraction $\sigma (\rm p\rm p \to \rm H \to {\mathrm{Z}} {\mathrm{Z}})=$ 50 fb. Lower panels show the ratio of data to the expected background. The shaded areas show the systematic and total statistical plus systematic uncertainties in the background estimation.

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Figure 5-d:
Distribution of the transverse mass $m_{\mathrm{T}}$ in the signal region for the $\geq$ 1-jet category for the $ 2 \ell 2 \nu $ channel, in the $\mu \mu $ final state. The points represent the data and the stacked histograms the expected background. The open histograms show the expected gluon-fusion and VBF signals for cross sections times branching fraction $\sigma (\rm p\rm p \to \rm H \to {\mathrm{Z}} {\mathrm{Z}})=$ 50 fb. Lower panels show the ratio of data to the expected background. The shaded areas show the systematic and total statistical plus systematic uncertainties in the background estimation.

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Figure 5-e:
Distribution of the transverse mass $m_{\mathrm{T}}$ in the signal region for the VBF-tagged category for the $ 2 \ell 2 \nu $ channel, in the ee final state. The points represent the data and the stacked histograms the expected background. The open histograms show the expected gluon-fusion and VBF signals for cross sections times branching fraction $\sigma (\rm p\rm p \to \rm H \to {\mathrm{Z}} {\mathrm{Z}})=$ 50 fb. Lower panels show the ratio of data to the expected background. The shaded areas show the systematic and total statistical plus systematic uncertainties in the background estimation.

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Figure 5-f:
Distribution of the transverse mass $m_{\mathrm{T}}$ in the signal region for the VBF-tagged category for the $ 2 \ell 2 \nu $ channel, in the $\mu \mu $ final state. The points represent the data and the stacked histograms the expected background. The open histograms show the expected gluon-fusion and VBF signals for cross sections times branching fraction $\sigma (\rm p\rm p \to \rm H \to {\mathrm{Z}} {\mathrm{Z}})=$ 50 fb. Lower panels show the ratio of data to the expected background. The shaded areas show the systematic and total statistical plus systematic uncertainties in the background estimation.

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Figure 6:
The efficiency times acceptance for signal events to pass the $X\rightarrow {\mathrm{Z}} {\mathrm{Z}} \rightarrow 4\ell $ (top) and $X\rightarrow {\mathrm{Z}} {\mathrm{Z}} \rightarrow 2\ell 2\mathrm{q} $ (bottom) selection as a function of the generated mass $m_{{\mathrm{Z}} {\mathrm{Z}}}^{\rm Gen}$, from ggH (left) and VBF (right) production modes.

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Figure 6-a:
The efficiency times acceptance for signal events to pass the $X\rightarrow {\mathrm{Z}} {\mathrm{Z}} \rightarrow 4\ell $ selection as a function of the generated mass $m_{{\mathrm{Z}} {\mathrm{Z}}}^{\rm Gen}$, from the ggH production mode.

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Figure 6-b:
The efficiency times acceptance for signal events to pass the $X\rightarrow {\mathrm{Z}} {\mathrm{Z}} \rightarrow 4\ell $ selection as a function of the generated mass $m_{{\mathrm{Z}} {\mathrm{Z}}}^{\rm Gen}$, from the VBF production mode.

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Figure 6-c:
The efficiency times acceptance for signal events to pass the $X\rightarrow {\mathrm{Z}} {\mathrm{Z}} \rightarrow 2\ell 2\mathrm{q} $ selection as a function of the generated mass $m_{{\mathrm{Z}} {\mathrm{Z}}}^{\rm Gen}$, from the ggH production mode.

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Figure 6-d:
The efficiency times acceptance for signal events to pass the $X\rightarrow {\mathrm{Z}} {\mathrm{Z}} \rightarrow 2\ell 2\mathrm{q} $ selection as a function of the generated mass $m_{{\mathrm{Z}} {\mathrm{Z}}}^{\rm Gen}$, from the VBF production mode.

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Figure 7:
Parameterization of the four-leptons invariant mass for ggH (left) and VBF (right) production mode, for $m_{H} =$ 450 GeV, $\Gamma _{H} = $ 10 GeV. The interference contributions from H(125) and gg $\to $ ZZ or VV $\rightarrow {\mathrm{Z}} {\mathrm{Z}} $ background are also shown. The signal cross section used corresponds to the limit obtained in the $4\ell $ final state.

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Figure 7-a:
Parameterization of the four-leptons invariant mass for the ggH production mode, for $m_{H} =$ 450 GeV, $\Gamma _{H} = $ 10 GeV. The interference contributions from H(125) and gg $\to $ ZZ or VV $\rightarrow {\mathrm{Z}} {\mathrm{Z}} $ background are also shown. The signal cross section used corresponds to the limit obtained in the $4\ell $ final state.

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Figure 7-b:
Parameterization of the four-leptons invariant mass for the VBF production mode, for $m_{H} =$ 450 GeV, $\Gamma _{H} = $ 10 GeV. The interference contributions from H(125) and gg $\to $ ZZ or VV $\rightarrow {\mathrm{Z}} {\mathrm{Z}} $ background are also shown. The signal cross section used corresponds to the limit obtained in the $4\ell $ final state.

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Figure 8:
Distribution of the missing transverse energy ${E_{\mathrm {T}}^{\text {miss}}}$ in the dilepton signal region. Points represent the data, stacked histograms the expected backgrounds and open histograms the expected signals.

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Figure 9:
Expected and observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and for several $\Gamma _ {\mathrm {X}} $ values with $f_{\rm VBF}$ being a free parameter (left) and fixed to 1 (right) with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels and combined.

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Figure 9-a:
Expected and observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and for $\Gamma _ {\mathrm {X}} = $ 0 GeV with $f_{\rm VBF}$ being a free parameter with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels and combined.

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Figure 9-b:
Expected and observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and for $\Gamma _ {\mathrm {X}} = $ 0 GeV with $f_{\rm VBF}$ fixed to 1 with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels and combined.

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Figure 9-c:
Expected and observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and for $\Gamma _ {\mathrm {X}} = $ 10 GeV with $f_{\rm VBF}$ being a free parameter with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels and combined.

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Figure 9-d:
Expected and observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and for $\Gamma _ {\mathrm {X}} = $ 10 GeV with $f_{\rm VBF}$ fixed to 1 with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels and combined.

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Figure 9-e:
Expected and observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and for $\Gamma _ {\mathrm {X}} = $ 100 GeV with $f_{\rm VBF}$ being a free parameter with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels and combined.

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Figure 9-f:
Expected and observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and for $\Gamma _ {\mathrm {X}} = $ 100 GeV with $f_{\rm VBF}$ fixed to 1 with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels and combined.

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Figure 10:
Observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and $\Gamma _ {\mathrm {X}} /m_ {\mathrm {X}} $ values with $f_{\rm VBF}$ being a free parameter (left) and fixed to 1 (right) with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for the $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels combined.

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Figure 10-a:
Observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and $\Gamma _ {\mathrm {X}} /m_ {\mathrm {X}} $ values with $f_{\rm VBF}$ being a free parameter with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for the $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels combined.

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Figure 10-b:
Observed upper limits at the 95% CL on the pp$\to {\mathrm {X}} \to {\mathrm{Z}} {\mathrm{Z}} $ cross section as a function of $m_ {\mathrm {X}} $ and $\Gamma _ {\mathrm {X}} /m_ {\mathrm {X}} $ values with $f_{\rm VBF}$ fixed to 1 with 35.9 fb$^{-1}$ of data at 13 TeV. The results are shown for the $4\ell $, $2\ell 2\mathrm{q} $ and $2\ell 2\nu $ channels combined.
Tables

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Table 1:
Sources of uncertainties considered in each of the channels included in this analysis. Uncertainties are given in percent. The numbers shown in ranges represent the uncertainties in different final states, categories. Most uncertainties affect the normalization of the data or simulated yields, those that affect the shape of kinematic distributions as well are labeled with (*).
Summary
A search for a new scalar resonance decaying to a pair of Z bosons is performed for a range of masses between 130 GeV and 3 TeV with the full data set recorded by the CMS experiment at 13 TeV during 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Three final states $\mathrm{Z}\mathrm{Z}\to 4\ell$, $2\ell2\mathrm{q}$, and $2\ell2\nu$ are used and combined in the analysis. Both gluon fusion and electroweak production of the scalar resonance are considered with a free parameter describing their relative cross sections. A dedicated categorization of events based on the kinematic properties of the associated jets is used to improve the sensitivity of the search. No significant excess of events is observed and limits are set on the production cross section for a wide range of masses and widths, and for different production mechanisms.
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Compact Muon Solenoid
LHC, CERN