CMS-PAS-SUS-23-013

CMS-PAS-SUS-23-013
Search for dark matter produced in association with a dark Higgs boson decaying into a bottom quark pair in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
CMS Collaboration
2025-08-15

Abstract: A search for dark matter produced in association with a dark Higgs boson decaying into a bottom quark pair has been performed in proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector during the 2016-2018 data-taking period at the CERN LHC. The analyzed data sample corresponds to an integrated luminosity of 138 fb$ ^{-1} $. The results are interpreted in terms of a novel theoretical model of dark matter production that, together with a spin-1 gauge boson mediator, predicts the existence of a Higgs-boson-like particle in the dark sector (i.e., a dark Higgs boson). This search focuses on an experimental signature with large missing transverse momentum from dark matter production and a resonant structure in the invariant mass of the bottom quark pair from the dark Higgs boson decay. Limits at the 95% confidence level on the signal strength for dark Higgs boson mass hypotheses below 160 GeV are set for the first time with CMS data. Values of the mediator mass up to 2.5-4.5 TeV are excluded depending on the dark Higgs boson mass.
Links: CDS record (PDF) ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Feynman diagram for the associated production of a $ \mathrm{H}_{\text{D}} $ boson and $ \chi $ particles. The interaction with SM quarks is mediated by a $ \mathrm{Z}^{'} $ boson, and the $ \mathrm{H}_{\text{D}} $ boson mixes with the SM Higgs boson through the $ \theta_{\text{h}} $ mixing angle. In this paper we focus on the decay of the $ \mathrm{H}_{\text{D}} $ boson into a b quark-antiquark pair, which is dominant at lower masses.
png pdf	Figure 2: Postfit $ m_{\text{SD}} $ distributions in bins of $ U $ for all three years combined. The upper panels present stacked postfit predictions for the backgrounds superimposed on the data. The lower panels present the ratio between the data and the background predictions. The ratio between the data and the postfit prediction is represented by the blue dots, while the ratio between the data and the prefit prediction is represented by the red ones. Only statistical uncertainties are shown.
png pdf	Figure 3: Expected and observed exclusion limits at the 95% CL on the signal strength $ \mu=\sigma/\sigma_\text{theo} $ as a function of $ m_{\mathrm{Z}^{'}} $ for a $ \mathrm{H}_{\text{D}} $ boson mass of 50 GeV. Only scenarios where the DM particle is more massive than the $ \mathrm{H}_{\text{D}} $ boson are considered. The black solid line indicates the observed exclusion boundary corresponding to $ \mu= $ 1. The black dashed and dotted lines represent the expected exclusion and the 68 and 95% CL intervals around the expected boundary, respectively. Parameter combinations corresponding to larger values of $ \mu $ are excluded.
png pdf	Figure 4: Expected and observed exclusion limits at the 95% CL on the signal strength $ \mu=\sigma/\sigma_\text{theo} $ as a function of $ m_{\mathrm{Z}^{'}} $ for a $ \mathrm{H}_{\text{D}} $ boson mass of 70 GeV. Only scenarios where the DM particle is more massive than the $ \mathrm{H}_{\text{D}} $ boson are considered. The black solid line indicates the observed exclusion boundary corresponding to $ \mu= $ 1. The black dashed and dotted lines represent the expected exclusion and the 68 and 95% CL intervals around the expected boundary, respectively. Parameter combinations corresponding to larger values of $ \mu $ are excluded.
png pdf	Figure 5: Expected and observed exclusion limits at the 95% CL on the signal strength $ \mu=\sigma/\sigma_\text{theo} $ as a function of $ m_{\mathrm{Z}^{'}} $ for a $ \mathrm{H}_{\text{D}} $ boson mass of 90 GeV. Only scenarios where the DM particle is more massive than the $ \mathrm{H}_{\text{D}} $ boson are considered. The black solid line indicates the observed exclusion boundary corresponding to $ \mu= $ 1. The black dashed and dotted lines represent the expected exclusion and the 68 and 95% CL intervals around the expected boundary, respectively. Parameter combinations corresponding to larger values of $ \mu $ are excluded.
png pdf	Figure 6: Expected and observed exclusion limits at the 95% CL on the signal strength $ \mu=\sigma/\sigma_\text{theo} $ as a function of $ m_{\mathrm{Z}^{'}} $ for a $ \mathrm{H}_{\text{D}} $ boson mass of 110 GeV. Only scenarios where the DM particle is more massive than the $ \mathrm{H}_{\text{D}} $ boson are considered. The black solid line indicates the observed exclusion boundary corresponding to $ \mu= $ 1. The black dashed and dotted lines represent the expected exclusion and the 68 and 95% CL intervals around the expected boundary, respectively. Parameter combinations corresponding to larger values of $ \mu $ are excluded.
png pdf	Figure 7: Expected and observed exclusion limits at the 95% CL on the signal strength $ \mu=\sigma/\sigma_\text{theo} $ as a function of $ m_{\mathrm{Z}^{'}} $ for a $ \mathrm{H}_{\text{D}} $ boson mass of 130 GeV. Only scenarios where the DM particle is more massive than the $ \mathrm{H}_{\text{D}} $ boson are considered. The black solid line indicates the observed exclusion boundary corresponding to $ \mu= $ 1. The black dashed and dotted lines represent the expected exclusion and the 68 and 95% CL intervals around the expected boundary, respectively. Parameter combinations corresponding to larger values of $ \mu $ are excluded.
png pdf	Figure 8: Expected and observed exclusion limits at the 95% CL on the signal strength $ \mu=\sigma/\sigma_\text{theo} $ as a function of $ m_{\mathrm{Z}^{'}} $ for a $ \mathrm{H}_{\text{D}} $ boson mass of 150 GeV. Only scenarios where the DM particle is more massive than the $ \mathrm{H}_{\text{D}} $ boson are considered. The black solid line indicates the observed exclusion boundary corresponding to $ \mu= $ 1. The black dashed and dotted lines represent the expected exclusion and the 68 and 95% CL intervals around the expected boundary, respectively. Parameter combinations corresponding to larger values of $ \mu $ are excluded.

Tables
png pdf	Table 1: Expected yields from background processes in the SR. The values shown are from Monte Carlo simulation and the uncertainties are statistical-only. The expected yields for a reference signal hypothesis with m$ _{Z'} = $ 1000 GeV, m$ _{h_{s}} = $ 130 GeV, and m$ _{DM} = $ 150 GeV are also reported.
png pdf	Table 2: Summary of requirements that define the different analysis regions. A "\checkmark" means the requirement is enforced; an "X" means the variable is left unconstrained in that region (the cut is not applied).
png pdf	Table 3: Summary of statistical and systematic uncertainties included in the analysis. The value given for each rate uncertainty is the pre-fit maximum value. Uncertainties in the shape of the distributions are instead labeled as such.

Summary

A search for physics beyond the standard model in events with a resonant pair of b quarks and large missing transverse momentum has been presented. A data set of proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $ is analyzed. A joint maximum likelihood fit spanning a set of signal and control regions is used to constrain the standard model background contributions to the data and to extract a possible signal. The result is interpreted in terms of exclusion limits at the 95% confidence level on the parameters of a model of production of a $ \mathrm{H}_{\text{D}} $ boson in association with dark matter particles. Values of the mediator mass of up to 2.5-4.5 TeV are excluded, depending on the mass of the $ \mathrm{H}_{\text{D}} $ boson and assuming couplings of $ g_\mathrm{q}= $ 0.25 between the mediator and quarks, and $ g_{\chi} = $ 1.0 between the mediator and the DM particles. \newpage

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