CMS-PAS-EXO-16-054

CMS-PAS-EXO-16-054
Search for Dark Matter produced in association with a Higgs boson decaying to two photons
CMS Collaboration
May 2017

Abstract: A search for the associated production of dark matter with a Higgs boson which decays into two photons is presented. The search uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Results are interpreted in the context of two dark matter models: a two-Higgs-doublet-Z' model where the Z' decays to a pseudoscalar and a standard model-like Higgs Boson and a baryonic Z' simplified model. The search is performed categorizing the events based on the amount of missing transverse momentum in order to also be sensitive to hypothetical signals with small amounts of missing transverse momentum. After the final selection, no significant evidence for dark matter particle production has been observed. Two-Higgs-doublet-Z' signals with a pseudoscalar mass of 300 GeV are excluded at 95% of CL for Z' masses below 900 GeV. Baryonic Z' models with a dark matter mass of 1 GeV are excluded at 95% of CL for Z' masses below 800 GeV.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Feynman diagrams for the benchmark DM signal models: baryonic Z' (left) and 2HDM (right).
png	Figure 1-a: Feynman diagram for the benchmark DM signal baryonic Z' model.
png	Figure 1-b: Feynman diagram for the benchmark DM signal 2HDM model.
png pdf	Figure 2: Distribution of the missing transverse momentum of the 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.
png pdf	Figure 3: The ${m_{\gamma \gamma }}$ distribution after all selection is applied in the low-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ (left) and high-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ (right) categories. The cross section 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.
png pdf	Figure 3-a: The ${m_{\gamma \gamma }}$ distribution after all selection is applied in the low-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ category. The cross section 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.
png pdf	Figure 3-b: The ${m_{\gamma \gamma }}$ distribution after all selection is applied in the high-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ category. The cross section 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.
png pdf	Figure 4: The power law (dashed black) fit to the data and SM h ${\rightarrow \gamma \gamma }$ contribution (solid red) for low-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ (left) and high-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ (right) categories. Shown in solid blue is the sum of the non-resonant and resonant shapes used to estimate the total background in this analysis.
png pdf	Figure 4-a: The power law (dashed black) fit to the data and SM h ${\rightarrow \gamma \gamma }$ contribution (solid red) for the low-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ category. Shown in solid blue is the sum of the non-resonant and resonant shapes used to estimate the total background in this analysis.
png pdf	Figure 4-b: The power law (dashed black) fit to the data and SM h ${\rightarrow \gamma \gamma }$ contribution (solid red) for the high-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ category. Shown in solid blue is the sum of the non-resonant and resonant shapes used to estimate the total background in this analysis.
png pdf	Figure 5: The upper limits on cross section for the 2HDM scenario as a function of $m_{{\mathrm{ Z }'} }$ for $m_{A} = $ 300 GeV. The theoretical cross section (blue) is calculated assuming $g_{{\mathrm{ Z }' } } = $ 0.8.
png pdf	Figure 6: The observed (expected) 95% CL limits on the signal strength ($ \sigma _{95\% CL}/\sigma _{th} $) for all 2HDM mass points shown in a grid of $m_{A}$ and $m_{Z'}$. The theoretical cross section for each point is calculated assuming $g_{{\mathrm{ Z }pr } } = $ 0.8.
png pdf	Figure 7: The upper limits on cross section for the baryonic Z' scenario as a function of $m_{{\mathrm{ Z }' } }$ for $m_{\chi } = $ 1 GeV. The theoretical cross section (blue) is calculated assuming $g_{q} = $ 0.25 and $sin(\theta )= $ 0.3.

Tables
png pdf	Table 1: Maximum allowed value of each variable used in barrel and endcap photon identification [26]. The ${p_{\mathrm {T}}}$ used in these formulas is expressed in GeV.
png pdf	Table 2: Optimized kinematic requirements for the low- and high-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ categories.
png pdf	Table 3: Expected background yields and observed amount of data in the ${m_{\gamma \gamma }}$ range of 122 to 128 GeV for low- and high-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ categories. The non-resonant background includes QCD, $\gamma \gamma $, $\gamma $+jet, and EWK backgrounds and is estimated from the fit to data. The irreducible background from the SM Higgs boson associated production is presented separated from the the SM Higgs boson production modes. For the resonant background contributions both the statistical and the systematic uncertainties are listed. As detailed in Sec. 6.1 we do not include any systematic uncertainty associated to the non-resonant background.
png pdf	Table 4: Efficiency times acceptance and statistical uncertainty for the 2HDM in both the low- and high-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ categories. Samples that have negligible efficiencies in the low-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ category are shown with a dash (/).
png pdf	Table 5: Efficiency times acceptance and statistical uncertainty for the Baryonic Z' model in both the low- and high-$ {p_{\mathrm {T}}^{\mathrm {miss}}}$ categories. Efficiencies are calculated for several Z' mass points for a fixed $m_{\chi } = $ 1 GeV.

Summary

A search for dark matter produced in association with a Higgs boson is presented. This analysis examines the case where the Higgs boson decays to two photons. The analysis is based on 35.9 fb$^{-1}$ of pp collisions collected by the CMS experiment in 2016 at $\sqrt{s} =$ 13 TeV. The results of the search are interpreted in terms of 2HDM and baryonic Z' simplified models of dark matter production.

After passing trigger requirements, events are selected if they contain two photon candidates passing kinematic requirements on the $p_{\mathrm{T}}/m_{\gamma\gamma}$ of the two photons, $ E_{\mathrm{T}}^{\text{miss}} $ and $p_{\mathrm{T}\gamma\gamma}$ obtained with an optimization study on the benchmark models. The selection optimization has been performed in both low- and high-$ E_{\mathrm{T}}^{\text{miss}} $ categories. A jet veto is applied to reduce the QCD background. Topological requirements avoid events with highly energetic jets collinear with the $ E_{\mathrm{T}}^{\text{miss}} $ for which the $ E_{\mathrm{T}}^{\text{miss}} $ could simply arise from a misreconstruction of the jet itself. Data driven techniques are applied to estimate the non-resonant background contributions. Limits on the signal cross section are calculated.

2HDM signals with $m_{A} = $ 300 GeV are excluded for Z' masses below 900 GeV. Baryonic Z' models are excluded for Z' masses below 800 GeV for a dark matter mass of 1 GeV. Results are mostly driven by the high-$ E_{\mathrm{T}}^{\text{miss}} $ category for the analyzed signal models.

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