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| CMS-PAS-EXO-16-012 | ||
| Search for dark matter in association with a Higgs boson decaying into a pair of bottom quarks at $\sqrt{s} =$ 13 TeV with the CMS detector | ||
| CMS Collaboration | ||
| July 2016 | ||
| Abstract: A search for the dark matter is performed using events with large missing transverse momentum and a Higgs boson decaying into a pair of bottom quarks in a data sample of proton-proton interactions at the centre-of-mass energy of 13 TeV collected with the CMS detector at the LHC in 2015. The data correspond to an integrated luminosity of 2.3 fb$^{-1}$. Results are interpreted in the framework of the Type-2 two-Higgs-doublet model where a high-mass resonance Z' decays into a pseudoscalar $\textrm{A}_{0}$ and the standard model Higgs boson. $\textrm{A}_{0}$ further decays into a pair of dark matter particles. The recoil of the Higgs boson against the dark matter particles is dependent on the mass of the resonance $m_{\textrm{Z}^{'}}$, therefore, the Higgs boson is reconstructed using a pair of small-radius jets for low transverse momentum and a large-radius jet for high transverse momentum. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 10 (2017) 180. The superseded preliminary plots can be found here. |
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| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Feynman diagram of a 2HDM with a new invisibly decaying pseudoscalar $\mathrm{A}_0$ from the decay of an on-shell resonance Z' giving rise to a Higgs+$ {E_{\mathrm {T}}^{\text {miss}}}$ signature. |
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Figure 2:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the W+jets (top left), Top (top right) and Z($\rightarrow \nu \nu $)+jets (bottom) CRs for the resolved regime. The bottom pads show the data-to-simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 350 GeV. |
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Figure 2-a:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the W+jets CR for the resolved regime. The bottom pads show the data-to-simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 350 GeV. |
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Figure 2-b:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the Top CR for the resolved regime. The bottom pads show the data-to-simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 350 GeV. |
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Figure 2-c:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the Z($\rightarrow \nu \nu $)+jets CR for the resolved regime. The bottom pads show the data-to-simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 350 GeV. |
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Figure 3:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the one-lepton (left) and Z($\rightarrow \nu \nu $)+jets (right) CRs for the boosted regime. The bottom pads show the data-to-simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 500 GeV. |
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Figure 3-a:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the one-lepton CR for the boosted regime. The bottom pads show the data-to-simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 500 GeV. |
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Figure 3-b:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the Z($\rightarrow \nu \nu $)+jets CR for the boosted regime. The bottom pads show the data-to-simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 500 GeV. |
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Figure 4:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the resolved (left) and the boosted (right) regimes in the signal region with three different $m_{ \mathrm{ Z }' } $ signal points overlaid. The cross section for the signal model uses $g_{\mathrm{ Z }' } = $ 0.8. The bottom pads show the data/simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 350 GeV for the resolved regime and $>$500 GeV for the boosted regime. |
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Figure 4-a:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the resolved regime in the signal region with three different $m_{ \mathrm{ Z }' } $ signal points overlaid. The cross section for the signal model uses $g_{\mathrm{ Z }' } = $ 0.8. The bottom pads show the data/simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 350 GeV for the resolved regime and $>$500 GeV for the boosted regime. |
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Figure 4-b:
Post-fit and pre-fit distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ expected from SM backgrounds and observed data for the boosted regime in the signal region with three different $m_{ \mathrm{ Z }' } $ signal points overlaid. The cross section for the signal model uses $g_{\mathrm{ Z }' } = $ 0.8. The bottom pads show the data/simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The last bin includes all events with ${E_{\mathrm {T}}^{\text {miss}}} > $ 350 GeV for the resolved regime and $>$500 GeV for the boosted regime. |
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Figure 5:
Expected and observed 95% CL limit on dark matter production cross section $\times $ branching ratio. For $m_{Z'} =$ 600, 800, 1000 GeV resolved analysis has been used while for other higher mass points boosted analysis is used. Theory cross section is calculated using two different approaches as explained earlier in section 1. |
| Tables | |
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Table 1:
Signal region event selections for resolved and boosted regimes. |
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Table 2:
SR and CRs summary used in the simultaneous fit for resolved and boosted analysis. |
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Table 3:
Post-fit background event yields and observed numbers of events in data for 2.3 fb$^{-1}$ for the resolved and the boosted regimes. The expected number of signal events, scaled to the nominal cross section with $g_{{\mathrm{ Z }' } }$ = 0.8, are also reported. |
| Summary |
| A search has been presented for an excess of events with large missing transverse momentum produced in association with the standard model Higgs boson decaying to bottom quarks in a data sample of proton-proton interactions at center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 2.3 fb$^{-1}$ collected by the CMS detector at the LHC in 2015. No significant deviation from standard model background prediction is observed. The search is interpreted in terms of dark matter production to place constraint on the parameter space of the Type-2 two-Higgs-doublet model. |
| Additional Figures | |
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Additional Figure 1:
$ {E_{\mathrm {T}}^{\text {miss}}} $ or transverse momentum of the Higgs boson for $m_{{\mathrm{ Z }' } } = $ 600 GeV, 1000 GeV and 1400 GeV. As the resonance mass increases $ {E_{\mathrm {T}}^{\text {miss}}} $ or transverse momentum of the Higgs boson increases. The distributions are shown for two different $m_{\chi }$ values, 10 GeV and 100 GeV and the $ {E_{\mathrm {T}}^{\text {miss}}} $ is almost independent of the dark matter mass considered. |
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Additional Figure 2:
$\Delta R$ between decay products of the Higgs boson for $m_{{\mathrm{ Z }' } } = $ 600 GeV, 1000 GeV and 1400 GeV. As the resonance mass increases the distance between two b quarks decreases because of high transverse momentum of the Higgs boson. The distributions are shown for two different $m_{\chi }$ values, 10 GeV and 100 GeV and $\Delta R$ is almost independent of the dark matter mass considered. |
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Additional Figure 3:
Post-fit and pre-fit distribution of the reconstructed Higgs boson candidate mass expected from SM backgrounds and observed data for the resolved regime with three different $m_{{\mathrm{ Z }' } }$ signal points overlaid. The cross section for the signal model uses $g_{{\mathrm{ Z }' } } = $ 0.8. The black band on the top pad shows the statistical uncertainity due to finite size of the simulation samples. The bottom pad shows the data/simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The first and third bins in the distribution shows the mass sidebands (Z($ \rightarrow \nu \nu $)+jets control region) and the second bin shows the region considered as signal region. |
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Additional Figure 4:
Post-fit and pre-fit distribution of the reconstructed Higgs boson candidate mass expected from SM backgrounds and observed data for the boosted regime with three different $m_{{\mathrm{ Z }' } }$ signal points overlaid. The cross section for the signal model uses $g_{{\mathrm{ Z }' } } = $ 0.8. The black band on the top pad shows the statistical uncertainity due to finite size of the simulation samples. The bottom pad shows the data/simulation ratio for pre-fit and post-fit background prediction with a dashed band corresponding to the uncertainty due to finite size of simulation samples and a gray band that adds the systematic uncertainty on the post-fit background prediction. The first and third bins in the distribution shows the mass sidebands (Z($\rightarrow \nu \nu $)+jets control region) and the second bin shows the region considered as signal region. |
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Additional Figure 5:
A picture of event observed in 2015 data after applying the boosted regime selection. The selected event has $ {E_{\mathrm {T}}^{\text {miss}}} $ of 425 GeV and a boosted jet with ${p_{\mathrm {T}}}$ of 486 GeV. Subjets inside the AK8 jet have $p_{\mathrm{T}}$ of 356 GeV and 132 GeV with $\Delta R$ separation of 0.61 between them. |
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