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CMS-PAS-EXO-20-013
Search for dark matter particles produced in association with a dark Higgs boson decaying into W$^{+}$W$^{-}$ in proton-proton collisions at $\sqrt{s}= $ 13 TeV with the CMS detector
Abstract: A search for dark matter (DM) particles is performed using events with a pair of W bosons and large missing transverse momentum. The analysis is based on proton-proton collision data at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC between 2016 and 2018 corresponding to an integrated luminosity of 137 fb$^{-1}$. No significant excess in the W$^{+}$W$^{-}$ dileptonic decay channel over the expected standard model background is observed. Limits are set on DM production in the context of the dark Higgs simplified model, with a dark Higgs mass above the W$^{+}$W$^{-}$ pair mass threshold.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Representative Born-level Feynman diagrams for the benchmark signal model considered in this note: $q \overline q \to \mathrm{Z'} \to s \chi \chi $, and $s \to \mathrm{W^{+}} \mathrm{W^{-}} $.

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Figure 1-a:
Representative Born-level Feynman diagram for the $q \overline q \to \mathrm{Z'} \to s \chi \chi $ signal model.

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Figure 1-b:
Representative Born-level Feynman diagram for the $s \to \mathrm{W^{+}} \mathrm{W^{-}} $ signal model.

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Figure 2:
Normalized $ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for a signal with $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV, after the event preselection criteria are applied. Predictions of the two main backgrounds of the analysis, WW and $ {{\mathrm{t} {}\mathrm{\bar{t}}} {}+{}\mathrm{t} \mathrm{W}} $, are shown as blue and yellow solid lines respectively. The last bin includes the overflow.

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Figure 3:
Kinematic distributions for selected events. The distributions show the leading (top left) and trailing (top right) lepton ${p_{\mathrm {T}}}$ ($ {{p_{\mathrm {T}}} ^{\ell \text { max}}} $ and $ {{p_{\mathrm {T}}} ^{\ell \text { min}}} $) for the full data set in SR1, the missing transverse momentum $ {{p_{\mathrm {T}}} ^\text {miss}} $ (middle left) and the transverse mass of the dilepton system plus $ {{p_{\mathrm {T}}} ^\text {miss}} $ (middle right), $ {{m_{\mathrm {T}}} ^{\ell\ell,\,\, {{p_{\mathrm {T}}} ^\text {miss}}}} $, for the full data set in SR2, and the dilepton invariant mass $ {m_{\ell \ell}} $ (bottom left) and the dilepton transverse momentum $ {{p_{\mathrm {T}}} ^{{\ell} {\ell}}}$ (bottom right) for the full data set in SR3. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV. The last bin includes the overflow.

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Figure 3-a:
Leading lepton ${p_{\mathrm {T}}}$ ($ {{p_{\mathrm {T}}} ^{\ell \text { max}}} $), for the full data set in SR1. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV. The last bin includes the overflow.

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Figure 3-b:
Trailing lepton ${p_{\mathrm {T}}}$ ($ {{p_{\mathrm {T}}} ^{\ell \text { min}}} $), for the full data set in SR1. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV. The last bin includes the overflow.

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Figure 3-c:
The missing transverse momentum $ {{p_{\mathrm {T}}} ^\text {miss}} $, for the full data set in SR2, The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV. The last bin includes the overflow.

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Figure 3-d:
The transverse mass of the dilepton system plus $ {{p_{\mathrm {T}}} ^\text {miss}} $ $ {{m_{\mathrm {T}}} ^{\ell\ell,\,\, {{p_{\mathrm {T}}} ^\text {miss}}}} $, for the full data set in SR2, The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV. The last bin includes the overflow.

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Figure 3-e:
The dilepton invariant mass $ {m_{\ell \ell}} $, for the full data set in SR3. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV. The last bin includes the overflow.

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Figure 3-f:
The dilepton transverse momentum $ {{p_{\mathrm {T}}} ^{{\ell} {\ell}}}$, for the full data set in SR3. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV. The last bin includes the overflow.

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Figure 4:
Kinematic distributions from the non-prompt validation region. The distributions show the angular distance between the two leptons (left), $ {\Delta R_{{\ell} {\ell}}} $, and the $\Delta \phi $ between the dilepton system and the $ {{p_{\mathrm {T}}} ^\text {miss}} $ (right) for the full data set. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The last bin includes the overflow.

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Figure 4-a:
The angular distance between the two leptons, $ {\Delta R_{{\ell} {\ell}}} $, in the non-prompt validation region for the full data set. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The last bin includes the overflow.

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Figure 4-b:
The $\Delta \phi $ between the dilepton system and the $ {{p_{\mathrm {T}}} ^\text {miss}} $ in the non-prompt validation region for the full data set. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The last bin includes the overflow.

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Figure 5:
Kinematic distributions for events entering in the different control regions. The distributions show the leading (top left) and trailing (top right) lepton ${p_{\mathrm {T}}}$ ($ {{p_{\mathrm {T}}} ^{\ell \text { max}}} $ and $ {{p_{\mathrm {T}}} ^{\ell \text { min}}} $) for the full data set in the W$^{+}$W$^{-}$ control region, the angular distance between the two leptons, $ {\Delta R_{{\ell} {\ell}}} $ (middle left), and the dilepton invariant mass $ {m_{\ell \ell}} $ (middle right) for the full data set in the Drell-Yan control region, and the missing transverse momentum $ {{p_{\mathrm {T}}} ^\text {miss}} $ (bottom left) and the dilepton transverse momentum $ {{p_{\mathrm {T}}} ^{{\ell} {\ell}}}$ (bottom right) for the full data set in the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {}+{}\mathrm{t} \mathrm{W}} $ control region. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The last bin includes the overflow.

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Figure 5-a:
The leading lepton ${p_{\mathrm {T}}}$ ($ {{p_{\mathrm {T}}} ^{\ell \text { max}}} $) for the full data set in the W$^{+}$W$^{-}$ control region. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The last bin includes the overflow.

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Figure 5-b:
The trailing lepton ${p_{\mathrm {T}}}$ ($ {{p_{\mathrm {T}}} ^{\ell \text { min}}} $) for the full data set in the W$^{+}$W$^{-}$ control region. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The last bin includes the overflow.

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Figure 5-c:
The angular distance between the two leptons, $ {\Delta R_{{\ell} {\ell}}} $, for the full data set in the Drell-Yan control region. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The last bin includes the overflow.

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Figure 5-d:
The dilepton invariant mass $ {m_{\ell \ell}} $, for the full data set in the Drell-Yan control region. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The last bin includes the overflow.

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Figure 5-e:
The missing transverse momentum $ {{p_{\mathrm {T}}} ^\text {miss}} $, for the full data set in the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {}+{}\mathrm{t} \mathrm{W}} $ control region. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The last bin includes the overflow.

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Figure 5-f:
The dilepton transverse momentum $ {{p_{\mathrm {T}}} ^{{\ell} {\ell}}}$, for the full data set in the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {}+{}\mathrm{t} \mathrm{W}} $ control region. The predicted yields are shown with their best fit normalizations from the simultaneous fit. The error bars on the data points represent the statistical uncertainty of the data, and the hatched areas represent the combined systematic and statistical uncertainty of the predicted yield in each bin. The last bin includes the overflow.

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Figure 6:
Unrolled and equally spaced binned $ {m_{\ell \ell}} $-$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ post-fit distributions for the full data set for in SR1 (top left), SR2 (top right), and SR3 (bottom). In each plot, every group of five bins (from left to right) corresponds to the $ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution in a $ {m_{\ell \ell}} $ region, placed in ascending order. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 6-a:
Unrolled and equally spaced binned $ {m_{\ell \ell}} $-$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ post-fit distributions for the full data set for in SR1. Every group of five bins (from left to right) corresponds to the $ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution in a $ {m_{\ell \ell}} $ region, placed in ascending order. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 6-b:
Unrolled and equally spaced binned $ {m_{\ell \ell}} $-$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ post-fit distributions for the full data set for in SR2. Every group of five bins (from left to right) corresponds to the $ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution in a $ {m_{\ell \ell}} $ region, placed in ascending order. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 6-c:
Unrolled and equally spaced binned $ {m_{\ell \ell}} $-$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ post-fit distributions for the full data set for in SR3. Every group of five bins (from left to right) corresponds to the $ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution in a $ {m_{\ell \ell}} $ region, placed in ascending order. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 7:
Combined observed (expected) exclusion regions at 95% CL for the dark Higgs model in the ($m_{s}$, $m_{\mathrm{Z'}}$) plane, marked by the solid red (black) line. The expected $\pm $ 1$\sigma $ band is shown as the thinner black line. Upper left: $m_{\chi} = $ 100 GeV, upper right: $m_{\chi} = $ 150 GeV, bottom left: $m_{\chi} = $ 200 GeV, bottom right: $m_{\chi} = $ 300 GeV.

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Figure 7-a:
Combined observed (expected) exclusion regions at 95% CL for the dark Higgs model in the ($m_{s}$, $m_{\mathrm{Z'}}$) plane, marked by the solid red (black) line. for $m_{\chi} = $ 100 GeV. The expected $\pm $ 1$\sigma $ band is shown as the thinner black line.

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Figure 7-b:
Combined observed (expected) exclusion regions at 95% CL for the dark Higgs model in the ($m_{s}$, $m_{\mathrm{Z'}}$) plane, marked by the solid red (black) line. for $m_{\chi} = $ 150 GeV. The expected $\pm $ 1$\sigma $ band is shown as the thinner black line.

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Figure 7-c:
Combined observed (expected) exclusion regions at 95% CL for the dark Higgs model in the ($m_{s}$, $m_{\mathrm{Z'}}$) plane, marked by the solid red (black) line. for $m_{\chi} = $ 200 GeV. The expected $\pm $ 1$\sigma $ band is shown as the thinner black line.

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Figure 7-d:
Combined observed (expected) exclusion regions at 95% CL for the dark Higgs model in the ($m_{s}$, $m_{\mathrm{Z'}}$) plane, marked by the solid red (black) line. for $m_{\chi} = $ 300 GeV. The expected $\pm $ 1$\sigma $ band is shown as the thinner black line.

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Figure 8:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distributions for the 2016 data set for the different signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-a:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-b:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-c:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-d:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-e:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-f:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-g:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-h:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-i:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-j:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-k:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 8-l:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2016 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distributions for the 2017 data set for the different signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-a:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-b:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-c:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-d:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-e:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-f:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-g:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-h:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-i:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-j:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-k:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 9-l:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2017 data set for one the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distributions for the 2018 data set for the different signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-a:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-b:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-c:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-d:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-e:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-f:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-g:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-h:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-i:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-j:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-k:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.

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Figure 10-l:
$ {{m_{\mathrm {T}}} ^{\ell \text { min},\, {{p_{\mathrm {T}}} ^\text {miss}}}} $ distribution for the 2018 data set for one of the signal regions. The black line indicates the signal prediction of $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV.
Tables

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Table 1:
Summary of the event preselection criteria. Kinematic quantities are measured in GeV.

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Table 2:
Data and background post-fit yields for each data period and for each signal region. Signal prediction corresponds to pre-fit yields for a sample with $m_{s} = $ 160 GeV, $m_{\chi} = $ 100 GeV, $m_{\mathrm{Z'}} = $ 500 GeV. The total post-fit uncertainty is shown for the total background.
Summary
A search for dark matter particles produced in association with a dark Higgs boson has been presented. A sample of proton-proton collision data at a center-of-mass energy of 13 TeV is used, corresponding to an integrated luminosity of 137 fb$^{-1}$. The decay mode of the dark Higgs boson to a W$^{+}$W$^{-}$ pair has been explored; this is the first time the CMS Collaboration explores this model. Results from the dileptonic decay channel of the W$^{+}$W$^{-}$ pair are presented. No significant deviation from the Standard Model prediction is observed, so upper limits at 95% confidence level on the production cross section of dark matter are set on the dark Higgs model parameters. This analysis extends the search to a wider DM mass range, from 100 GeV to 300 GeV. The most stringent limit is set for a $m_{DM} = $ 150 GeV, excluding $m_{s}$ masses up to $\approx $300 GeV in a mass range $\approx $480 $< m_{\mathrm{Z'}} < $ 1200 GeV, and up to $m_{\mathrm{Z'}} \approx $ 2000 GeV for a $m_{s} = $ 160 GeV.
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