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| CMS-PAS-EXO-16-038 | ||
| Search for dark matter in Z+$E_\mathrm{T}^\mathrm{miss}$ events using 12.9 fb$^{-1}$ of 2016 data | ||
| CMS Collaboration | ||
| August 2016 | ||
| Abstract: A search for new physics in events with a Z boson produced in association with large missing transverse momentum with the CMS experiment at the LHC is presented. This search is interpreted in a simplified model with a spin-1 dark matter mediator and in a model with a standard model Higgs-like scalar particle, each produced in association with the Z boson and decaying invisibly. The search is based on a 2016 data sample of proton-proton collisions at $ \sqrt{s} = $ 13 TeV corresponding to an integrated luminosity of 12.9 fb$^{-1}$. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1-a:
a: Distribution of the $ { {E_\mathrm {T}}^{\mathrm {miss}}}$ after the full selection except that 50 GeV $ < { {E_\mathrm {T}}^{\mathrm {miss}}} < $ 100 GeV. b: The $ { {E_\mathrm {T}}^{\mathrm {miss}}}$ in the signal region. The error bars represent statistical uncertainty, and the shaded bands represent systematic uncertainty. The histogram stack correspond to the sum of all background predictions, the dots are the data, the red line is the prediction for the $ {\mathrm {Z}} (\ell \ell ) {\mathrm {H}}$ ($m_H =$ 125 GeV) signal, and the dashed green line is the prediction for the DM signal for the simplified model with vector mediator with $(m_{\chi }, M_{V}) =$ (150, 500) GeV. The DM signal yield is multiplied by a factor three. |
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Figure 1-b:
a: Distribution of the $ { {E_\mathrm {T}}^{\mathrm {miss}}}$ after the full selection except that 50 GeV $ < { {E_\mathrm {T}}^{\mathrm {miss}}} < $ 100 GeV. b: The $ { {E_\mathrm {T}}^{\mathrm {miss}}}$ in the signal region. The error bars represent statistical uncertainty, and the shaded bands represent systematic uncertainty. The histogram stack correspond to the sum of all background predictions, the dots are the data, the red line is the prediction for the $ {\mathrm {Z}} (\ell \ell ) {\mathrm {H}}$ ($m_H =$ 125 GeV) signal, and the dashed green line is the prediction for the DM signal for the simplified model with vector mediator with $(m_{\chi }, M_{V}) =$ (150, 500) GeV. The DM signal yield is multiplied by a factor three. |
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Figure 2-a:
The 95%CL observed limits on signal strength $\sigma ^{\rm obs}/\sigma ^{\rm th}$ in both vector (left) and axial-vector (right) coupling scenario, for coupling $g_{\rm q}= $ 0.25. The expected exclusion curves for unity signal strength are shown as a reference. |
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Figure 2-b:
The 95%CL observed limits on signal strength $\sigma ^{\rm obs}/\sigma ^{\rm th}$ in both vector (left) and axial-vector (right) coupling scenario, for coupling $g_{\rm q}= $ 0.25. The expected exclusion curves for unity signal strength are shown as a reference. |
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Figure 3-a:
The 95%CL observed limits on signal strength $\sigma ^{\rm obs}/\sigma ^{\rm th}$ in both vector (left) and axial-vector (right) coupling scenario, for coupling $g_{\rm q}= $ 1. The expected exclusion curves for unity signal strength are shown as a reference. |
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Figure 3-b:
The 95%CL observed limits on signal strength $\sigma ^{\rm obs}/\sigma ^{\rm th}$ in both vector (left) and axial-vector (right) coupling scenario, for coupling $g_{\rm q}= $ 1. The expected exclusion curves for unity signal strength are shown as a reference. |
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Figure 4-a:
Observed 90% CL limits on the DM-nucleon scattering cross sections in both spin-independent (left) and spin-dependent (right) cases, assuming a mediator-quark coupling constant $g_{\rm q} = $ 0.25 and mediator-DM coupling constant $g_{\chi } = 1$. Limits from the LUX [56], CDMSLite [57], PandaX-II [58], and CRESST-II [59] experiments are shown for the spin-independent case. Limits from the Super-Kamiokande [60], PICO-2L [61], PICO-60 [62], and IceCube [63] experiments are shown for the spin-dependent case. |
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Figure 4-b:
Observed 90% CL limits on the DM-nucleon scattering cross sections in both spin-independent (left) and spin-dependent (right) cases, assuming a mediator-quark coupling constant $g_{\rm q} = $ 0.25 and mediator-DM coupling constant $g_{\chi } = 1$. Limits from the LUX [56], CDMSLite [57], PandaX-II [58], and CRESST-II [59] experiments are shown for the spin-independent case. Limits from the Super-Kamiokande [60], PICO-2L [61], PICO-60 [62], and IceCube [63] experiments are shown for the spin-dependent case. |
| Tables | |
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Table 1:
Summary of selections used in the analysis. |
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Table 2:
Summary of systematic uncertainties. Each background uncertainty represents the variation of the relative yields of the particular background components. The signal uncertainties represent the relative variations in the signal acceptance. The symbol ``--'' indicates that the systematic uncertainty is not applicable. The impact of the each group of systematic uncertainties is calculated by performing a maximum likelihood fit to obtain the signal strength with each parameter separately varied up and down within its uncertainty. The number given in the impact column is the relative change of the expected best fit signal strength that is introduced by the variation for a the simplified model signal scenario with a vector mediator of mass 200 GeV and DM of mass 50 GeV. |
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Table 3:
Observed number of events, background estimates, and signal predictions. Both statistical and systematic uncertainties are reported. The DM signal yields for simplified models with vector and axial-vector mediators are given for $(m_{\chi }, M_{A/V}) =$ (50, 200), (150, 500) (all masses in GeV ). |
| Summary |
| A search for new physics in events with a Z boson produced in association with large missing transverse momentum with the CMS experiment at the LHC has been presented. This search is interpreted in a simplified model with a spin-1 dark matter mediator and in a model with a SM Higgs-like scalar particle, each produced in association with the Z boson and decaying invisibly. The search is based on a 2016 data sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV corresponding to an integrated luminosity of 12.9$\pm$0.8 fb$^{-1}$. \bibliography{auto_generated} |
| Additional Figures | |
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Additional Figure 1-a:
Comparison between the 2015 and 2016 analyses of the 95% CL observed and expected limits on signal strength $\sigma ^{obs}/\sigma ^{th}$ in both vector (a) and axial-vector (b) coupling scenario, for coupling $g_{q}=$ 1. |
png |
Additional Figure 1-b:
Comparison between the 2015 and 2016 analyses of the 95% CL observed and expected limits on signal strength $\sigma ^{obs}/\sigma ^{th}$ in both vector (a) and axial-vector (b) coupling scenario, for coupling $g_{q}=$ 1. |
png |
Additional Figure 2-a:
Comparison between the 2015 and 2016 analyses of the 95% CL observed and expected limits on signal strength $\sigma ^{obs}/\sigma ^{th}$ in both vector (a) and axial-vector (b) coupling scenario, for coupling $g_{q}=$ 0.25. |
png |
Additional Figure 2-b:
Comparison between the 2015 and 2016 analyses of the 95% CL observed and expected limits on signal strength $\sigma ^{obs}/\sigma ^{th}$ in both vector (a) and axial-vector (b) coupling scenario, for coupling $g_{q}=$ 0.25. |
png pdf |
Additional Figure 3:
Expected and observed 95% CL upper limits on the quark-induced production cross section times branching ratio, $\sigma _{{\mathrm{ Z } } \rm H(\to \rm invisible)} \times \mathrm {BR}(\rm H \to {\rm invisible})$ as a function of the Higgs boson mass. The gray band indicates the SM Higgs boson mass, where the limits shown in the plot can only be considered as approximate, as, e.g. gluon fusion production mechanism is not considered. |
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