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Search for dark matter in final states with a Higgs boson decaying to a pair of b-jets and missing transverse momentum at the HL-LHC
Abstract: We perform a projection study for the sensitivity of the upgraded CMS detector to new physics in a mono-Higgs sector, h $\to$ bb plus missing transverse momentum final state, at the HL-LHC. The focus lies on signals with boosted Higgs bosons, resulting in a large radius jet containing both b quarks that can are identified as originating from a Higgs boson. The search is sensitive to a variety of BSM models and in this analysis the results are interpreted in terms of 2HDM+a model. We find that with a data set corresponding to 3000 fb$^{-1}$, $m_{\text{A}}$ masses from 750 to 2000 GeV could be excluded for $m_{\text{a}} = $ 250 GeV and $m_{\text{A}}$ masses from 1250 to 1600 GeV could be excluded for $m_{\text{a}} = $ 500 GeV. The 2HDM+a signals with $m_{\text{a}} = $ 250 and $m_{\text{A}}= $ 1000-1600 GeV, which are not yet excluded, could reach a significance near 5$\sigma$.
Figures & Tables Summary References CMS Publications

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Figure 1:
The pseudoscalar A decaying into the light pseudoscalar a and the observed Higgs boson h in a 2HDM+a model.

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Figure 2:
SM background predictions and expectations for two signal benchmark scenarios: 2HDM+a model with $m_{\mathrm{A} }=$ 1750 GeV, $m_{{\mathrm{a}}} = $ 250 GeV (solid line) and $m_{\mathrm{A} }=$ 1750 GeV, $m_{{\mathrm{a}}} = $ 750 GeV (dashed line). The systematic and statistical uncertainties in each bin after fitting are given by the shaded regions. The lower panel shows the relative uncertainties in each bin. The last bin of each ${m_{\mathrm {T}}}$ distribution contains the overflow.

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Figure 3:
Expected limits on the signal strength for a 2HDM+a model of DM production in association with $\mathrm{h} \to \mathrm{b} {}\mathrm{\bar{b}} + {{p_{\mathrm {T}}} ^\text {miss}} $. Limits are produced for varying values of $m_{\mathrm{A} }$ and $m_{{\mathrm{a}}}$ with $\sin\theta =$ 0.35, $\tan\beta =$ 1, and $m_{\chi}=$ 10 GeV. The shaded region reflects the 1$\sigma $ uncertainty band.

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Figure 4:
Expected significance of a 2HDM+a model of DM production in association with $\mathrm{h} \to \mathrm{b} {}\mathrm{\bar{b}} + {{p_{\mathrm {T}}} ^\text {miss}} $ produced for varying values of $m_{\mathrm{A} }$ and $m_{{\mathrm{a}}}$ with $\sin\theta =$ 0.35, $\tan\beta =$ 1, and $m_\chi =$ 10 GeV.

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Table 1:
Summary of the event selection.

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Table 2:
Summary of the effect of the systematic uncertainties used in this analysis on the yields.
This analysis is a search for Higgs boson decays into a pair of b quarks with high ${p_{\mathrm{T}}}^{\text{miss}}$ to probe the sensitivity of the HL-LHC to the production of dark matter in association with the Higgs boson. Several advances in technology and Phase-2 upgrades to the CMS detector will improve the ability to search for this final state, including improved heavy object tagging and increased geometric acceptance in the detector during the HL-LHC era. We interpret our results through a two Higgs doublet model, extended by a light pseudoscalar boson (2HDM+\mathrm{a}), by determining limits on the cross-section of the associated production for various masses of pseudoscalars a and A. We determine that the Phase-2 upgrades will enable the exclusion of a wide range of mass points. $m_{\mathrm{A} }$ values between 750 and 2000 GeV could be excluded for $m_{\mathrm{a}} = $ 250, while $m_{\mathrm{A} }$ values between 1250 and 1600 GeV could be excluded for $m_{\mathrm{a}} = $ 500. Signal points unconstrained by Run 2 searches with $m_{\mathrm{a}} = $ 250 GeV and $m_{\mathrm{A} }$ between 1000-1600 GeV could reach a significance close to 5$\sigma$.
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