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CMS-PAS-EXO-16-055
Search for dark matter produced in association with a Higgs boson decaying to $\gamma\gamma$ or $\tau^+\tau^-$ at $\sqrt{s}= $ 13 TeV with the CMS detector
Abstract: A search for dark matter is performed by looking for events in pp collisions with large missing transverse momentum and a recoiling Higgs boson that decays to either a pair of photons or a pair of tau leptons. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$ collected in 2016 by the CMS experiment at the CERN LHC at a center-of-mass energy of 13 TeV. No significant excess over the expected standard model background is observed. Results are interpreted in the context of two benchmark simplified models. Upper limits with 95% confidence level are presented for the signal production cross section times branching fraction. Results are also interpreted in terms of 90% confidence level limits on the spin-independent dark matter-nucleon cross section as a function of dark matter mass. This is the first search for dark matter produced in association with a Higgs boson decaying to two tau leptons.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Leading order Feynman diagrams for DM ($\chi $) associated production with a Higgs boson ($h$) for the two theoretical models considered in this analysis: $Z'$-2HDM (left) and baryonic $Z'$ (right).

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Figure 1-a:
Leading order Feynman diagram for DM ($\chi $) associated production with a Higgs boson ($h$) for the two theoretical models considered in this analysis: $Z'$-2HDM.

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Figure 1-b:
Leading order Feynman diagram for DM ($\chi $) associated production with a Higgs boson ($h$) for the two theoretical models considered in this analysis: baryonic $Z'$.

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Figure 2:
Distribution of the $ {{p_{\mathrm {T}}} ^\text {miss}} $ for events passing all other selection criteria. The cross sections of the signals are set to 1 pb. The total MC background is normalized to the integral of the data. Only the MC statistical uncertainties on the total background are shown in the hatched bands. The data-to-simulation ratio is shown in the lower panel.

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Figure 3:
The background-only fit to data is performed, for low-$ {{p_{\mathrm {T}}} ^\text {miss}} $ (left) and high-$ {{p_{\mathrm {T}}} ^\text {miss}} $ (right) categories, with the sum of a power law (dashed black) fit function to describe the nonresonant contribution and a resonant shape, taken from simulation, to take into account the SM ${h \rightarrow \gamma \gamma}$ contribution (solid red). The SM Higgs contribution is fixed to the theory prediction in the statistical analysis. The sum of the nonresonant and resonant shapes (solid blue) is used to estimate the total background in this analysis.

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Figure 3-a:
The background-only fit to data is performed, for the low-$ {{p_{\mathrm {T}}} ^\text {miss}} $ category, with the sum of a power law (dashed black) fit function to describe the nonresonant contribution and a resonant shape, taken from simulation, to take into account the SM ${h \rightarrow \gamma \gamma}$ contribution (solid red). The SM Higgs contribution is fixed to the theory prediction in the statistical analysis. The sum of the nonresonant and resonant shapes (solid blue) is used to estimate the total background in this analysis.

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Figure 3-b:
The background-only fit to data is performed, for the high-$ {{p_{\mathrm {T}}} ^\text {miss}} $ category, with the sum of a power law (dashed black) fit function to describe the nonresonant contribution and a resonant shape, taken from simulation, to take into account the SM ${h \rightarrow \gamma \gamma}$ contribution (solid red). The SM Higgs contribution is fixed to the theory prediction in the statistical analysis. The sum of the nonresonant and resonant shapes (solid blue) is used to estimate the total background in this analysis.

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Figure 4:
Distributions of the total transverse mass in the signal region for the $ {{\mu}} {{\tau}_{\rm h}} $ (top left), $ {\mathrm {e}} {{\tau}_{\rm h}} $ (top right), and $ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ (bottom) final states. The overflow of the distribution is included in the final 400-500 GeV bin.

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Figure 4-a:
Distribution of the total transverse mass in the signal region for the $ {{\mu}} {{\tau}_{\rm h}} $ final state. The overflow of the distribution is included in the final 400-500 GeV bin.

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Figure 4-b:
Distribution of the total transverse mass in the signal region for the $ {\mathrm {e}} {{\tau}_{\rm h}} $ final state. The overflow of the distribution is included in the final 400-500 GeV bin.

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Figure 4-c:
Distribution of the total transverse mass in the signal region for the $ {{\tau}_{\rm h}} {{\tau}_{\rm h}} $ final state. The overflow of the distribution is included in the final 400-500 GeV bin.

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Figure 5:
Expected and observed 95% CL upper limits on $Z'$-2HDM dark matter production cross section for the $ {h \rightarrow \gamma \gamma} $ channel, $ {h \rightarrow \tau ^+\tau ^-} $ channel, and their combined exclusion.

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Figure 6:
Observed 95% CL upper limits on $Z'$-2HDM signal strength for the $ {h \rightarrow \gamma \gamma} $ (left), $ {h \rightarrow \tau ^+\tau ^-} $ (right), and combination of the two channels (lower center). The observed (expected) two-dimensional exclusion curves are shown with thick red (dashed black) lines. The plus and minus one standard deviation expected exclusion curves are also shown as thin black lines. The region below the lines is excluded.

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Figure 6-a:
Observed 95% CL upper limits on $Z'$-2HDM signal strength for the $ {h \rightarrow \gamma \gamma} $. The observed (expected) two-dimensional exclusion curves are shown with thick red (dashed black) lines. The plus and minus one standard deviation expected exclusion curves are also shown as thin black lines. The region below the lines is excluded.

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Figure 6-b:
Observed 95% CL upper limits on $Z'$-2HDM signal strength for the $ {h \rightarrow \tau ^+\tau ^-} $. The observed (expected) two-dimensional exclusion curves are shown with thick red (dashed black) lines. The plus and minus one standard deviation expected exclusion curves are also shown as thin black lines. The region below the lines is excluded.

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Figure 6-c:
Observed 95% CL upper limits on $Z'$-2HDM signal strength for the combination of the $ {h \rightarrow \gamma \gamma} $ and $ {h \rightarrow \tau ^+\tau ^-} $ channels. The observed (expected) two-dimensional exclusion curves are shown with thick red (dashed black) lines. The plus and minus one standard deviation expected exclusion curves are also shown as thin black lines. The region below the lines is excluded.

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Figure 7:
Expected and observed 95% CL upper limits on baryonic $Z'$ dark matter production cross section for the $ {h \rightarrow \gamma \gamma} $ channel, $ {h \rightarrow \tau ^+\tau ^-} $ channel, and their combined exclusion.

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Figure 8:
Observed 95% CL upper limits on $Z'$ signal strength for the $ {h \rightarrow \gamma \gamma} $ (left), $ {h \rightarrow \tau ^+\tau ^-} $ (right), and combination of the two channels (lower center). The observed (expected) two-dimensional exclusion curves are shown with thick red (dashed black) lines. The plus and minus one standard deviation expected exclusion curves are also shown as thin black lines. The region below the lines is excluded.

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Figure 8-a:
Observed 95% CL upper limits on $Z'$ signal strength for the $ {h \rightarrow \gamma \gamma} $ channel. The observed (expected) two-dimensional exclusion curves are shown with thick red (dashed black) lines. The plus and minus one standard deviation expected exclusion curves are also shown as thin black lines. The region below the lines is excluded.

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Figure 8-b:
Observed 95% CL upper limits on $Z'$ signal strength for the $ {h \rightarrow \tau ^+\tau ^-} $ channel. The observed (expected) two-dimensional exclusion curves are shown with thick red (dashed black) lines. The plus and minus one standard deviation expected exclusion curves are also shown as thin black lines. The region below the lines is excluded.

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Figure 8-c:
Observed 95% CL upper limits on $Z'$ signal strength for the combination of the two channels $ {h \rightarrow \gamma \gamma} $ $ {h \rightarrow \tau ^+\tau ^-} $ channels. The observed (expected) two-dimensional exclusion curves are shown with thick red (dashed black) lines. The plus and minus one standard deviation expected exclusion curves are also shown as thin black lines. The region below the lines is excluded.

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Figure 9:
The 90% CL exclusion limits on the DM-nucleon SI scattering cross section as a function of $m_{\rm {DM}}$. Results obtained in this analysis are compared with those from direct detection experiments. The latter exclude the regions above the curves. Limits from CDMSLite [62], LUX [63], XENON-1T [64], PandaX-II [65], and CRESST-II [66] are shown.
Tables

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Table 1:
Optimized kinematic requirements for the low- and high-$ {{p_{\mathrm {T}}} ^\text {miss}} $ categories.

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Table 2:
Kinematic selection requirements for the three $ {\tau} {\tau}$ decay channels. The online threshold requirement for the trigger is given in the first column by the number inside the parentheses.

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Table 3:
Systematic uncertainties affecting the various samples in the ${h \rightarrow \gamma \gamma}$ channel.

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Table 4:
Systematic uncertainties affecting the various samples in the ${h \rightarrow \tau ^+\tau ^-}$ channel.

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Table 5:
Expected background yields and observed number of events in the ${m_{\gamma \gamma}}$ range of 122 to 128 GeV for low- and high-$ {{p_{\mathrm {T}}} ^\text {miss}} $ categories. The nonresonant background includes QCD, $\gamma \gamma $, ${\gamma + \text {jet}}$, and electroweak backgrounds and is estimated from the analytic function fit to the data. The irreducible background from the SM Higgs boson associated production is presented separated from the other SM $h$ production modes. For the resonant background contributions both the statistical and the systematic uncertainties are listed. The systematic uncertainty associated to the nonresonant background is not included.

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Table 6:
Estimated background yields for $M_{T,tot} > $ 260 GeV in the signal region for 35.9 fb$^{-1}$ of 2016 data. The total expected yields include the statistical and systematic uncertainties.

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Table 7:
The expected signal yields and A$\times \epsilon $ for the two benchmark models.
Summary
A search for dark matter produced in association with a Higgs boson has been performed. The study presented examines the case where the Higgs boson decays to either two photons or two tau leptons. This analysis is based on 35.9 fb$^{-1}$ of pp collision data collected with the CMS detector during 2016 at $\sqrt{s} = $ 13 TeV. The results of the search are interpreted in terms of $Z'$-2HDM and baryonic $Z'$ simplified models of dark matter production.

In the ${h \rightarrow \gamma\gamma} $ channel, a slight excess is observed at low-$ {p_{\mathrm{T}}}^{\text{miss}} $. However, the results are driven by the high-$ {p_{\mathrm{T}}}^{\text{miss}} $ region where no excess is observed. No significant deviation from the standard model background is observed in the ${h \rightarrow \tau^+\tau^-} $ channel. A statistical combination of the two channels was performed and these results were used to produce upper limits on DM production. Limits on the signal production cross section are calculated for both simplified models. For the $Z'$-2HDM signal, with $m_A = $ 300 GeV and $m_{DM} = $ 100 GeV, $Z'$ masses up to 1265 GeV are excluded at 95% CL. For the baryonic $Z'$ model, with $m_{DM} = $ 1 GeV, $Z'$ masses up to 815 GeV are excluded. This is the first search for dark matter produced in association with a Higgs boson decaying to two tau leptons.
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Compact Muon Solenoid
LHC, CERN