CMS-SUS-23-008

CMS-SUS-23-008 ; CERN-EP-2024-206
Search for dark matter produced in association with a pair of bottom quarks in proton-proton collisions at $ \sqrt{s} = $ 13 TeV
CMS Collaboration
29 August 2024
Submitted to J. High Energy Phys.
Abstract: A search for dark matter (DM) particles produced in association with bottom quarks is presented. The analysis uses proton-proton collision data at a center-of-mass energy of $ \sqrt{s}= $ 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The search is performed in the final state with large missing transverse momentum and a pair of jets originating from bottom quarks. No significant excess of data is observed with respect to the standard model expectation. Results are interpreted in the context of a type-II two-Higgs-doublet model with an additional light pseudoscalar (2HDM+a). An upper limit is set on the mass of the lighter pseudoscalar, excluding masses up to 260 GeV at 95% confidence level. This is the first search at the LHC to probe DM produced in association with two nonresonant bottom quarks in the 2HDM+a model. Sensitivity to the parameter space with the ratio of the vacuum expectation values of the two Higgs doublets, $ \tan\beta $, greater than 15 is achieved, capitalizing on the enhancement of couplings between pseudoscalars and bottom quarks with high $ \tan\beta $.
Links: e-print arXiv:2408.17336 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Leading Feynman diagrams for the $ \mathrm{b}\overline{\mathrm{b}}+\chi{\overline{\chi}} $ process in the 2HDM+a model.
png pdf	Figure 1-a: Leading Feynman diagrams for the $ \mathrm{b}\overline{\mathrm{b}}+\chi{\overline{\chi}} $ process in the 2HDM+a model.
png pdf	Figure 1-b: Leading Feynman diagrams for the $ \mathrm{b}\overline{\mathrm{b}}+\chi{\overline{\chi}} $ process in the 2HDM+a model.
png pdf	Figure 2: Normalized (to unity) shape of generator-level $ p_{\mathrm{T}}^\text{miss} $ distribution for two illustrative lighter pseudoscalar masses $ m_{\textrm{a}} $ (left) and for five illustrative DM masses $ m_{\chi} $ (right).
png pdf	Figure 2-a: Normalized (to unity) shape of generator-level $ p_{\mathrm{T}}^\text{miss} $ distribution for two illustrative lighter pseudoscalar masses $ m_{\textrm{a}} $ (left) and for five illustrative DM masses $ m_{\chi} $ (right).
png pdf	Figure 2-b: Normalized (to unity) shape of generator-level $ p_{\mathrm{T}}^\text{miss} $ distribution for two illustrative lighter pseudoscalar masses $ m_{\textrm{a}} $ (left) and for five illustrative DM masses $ m_{\chi} $ (right).
png pdf	Figure 3: Definition of SR1 and SR2 in terms of jet multiplicity (left), and CR and SR definition in the lepton multiplicity and additional jet multiplicity plane (right). The categories depend on the number and flavor of leptons, and the number of jets in an event.
png pdf	Figure 3-a: Definition of SR1 and SR2 in terms of jet multiplicity (left), and CR and SR definition in the lepton multiplicity and additional jet multiplicity plane (right). The categories depend on the number and flavor of leptons, and the number of jets in an event.
png pdf	Figure 3-b: Definition of SR1 and SR2 in terms of jet multiplicity (left), and CR and SR definition in the lepton multiplicity and additional jet multiplicity plane (right). The categories depend on the number and flavor of leptons, and the number of jets in an event.
png pdf	Figure 4: QCD background contribution in the QCD CR (black and pink dots) in the 2b category using 2017 data. The exponential is fitted in the range $ \min(\Delta\phi (\text{jet}, {\vec p}_{\mathrm{T}}^{\kern1pt\text{miss}}) ) < $ 0.3, checked to fit well in the range 0.3 $ < \min(\Delta\phi (\text{jet}, {\vec p}_{\mathrm{T}}^{\kern1pt\text{miss}}) ) < $ 0.5, and extrapolated to the SRs for $ \min(\Delta\phi (\text{jet}, {\vec p}_{\mathrm{T}}^{\kern1pt\text{miss}}) ) > $ 0.5. The process is performed for the 1b as well as 2b categories for all years.
png pdf	Figure 5: Observed and predicted $ p_{\mathrm{T}}^\text{miss} $ ($ U $) distributions in the 1b category. The red lines divide the plot into three parts: the first part shows the SR, the second part the $ \mathrm{Z}(\ell\ell)+\text{jets} $ CR, and the third part the $ \mathrm{W}(\ell\nu)+\text{jets} $ CR. The bottom plot shows the ratio of observed and predicted (both postfit and prefit) distributions along with an uncertainty band that includes both the systematic and statistical components.
png pdf	Figure 6: Observed and predicted $ \cos\Theta^{*} $ distributions in the 2b category. The red lines divide the plot into three parts: the first part shows the SR, the second part the $ \mathrm{Z}(\nu\nu)+\text{jets} $ CR, and the third part the $ \mathrm{t} \overline{\mathrm{t}} $ CR. The bottom plot shows the ratio of observed and predicted (both postfit and prefit) distributions along with an uncertainty band that includes both the systematic and statistical components.
png pdf	Figure 7: The 95% CL upper limit on the signal strength modifier of DM produced in association with a pair of bottom quarks for $ m_{\textrm{A}}= $ 600 GeV, $ \sin\theta= $ 0.7, $ m_{\chi}= $ 1 GeV, and $ \tan\beta= $ 35, for the combination of SR1 and SR2. The green and yellow bands show the $ \pm $ 1 and $ \pm $ 2 standard deviations from expected limits. The mass points below the red line are excluded.
png pdf	Figure 8: Observed and expected upper limits at 95% CL on the signal strength in the $ m_{\textrm{a}} $-$ \tan\beta $ (upper left), $ m_{\textrm{a}} $-$ \sin\theta $ (upper right), and $ m_{\textrm{a}} $-$ m_{\chi} $ (lower) planes. The shaded area bounded by solid black line is excluded, with, the dotted grey line ($ m_{\textrm{a}} = 2m_{\chi} $) separating on-shell and off-shell productions for the lower plot.
png pdf	Figure 8-a: Observed and expected upper limits at 95% CL on the signal strength in the $ m_{\textrm{a}} $-$ \tan\beta $ (upper left), $ m_{\textrm{a}} $-$ \sin\theta $ (upper right), and $ m_{\textrm{a}} $-$ m_{\chi} $ (lower) planes. The shaded area bounded by solid black line is excluded, with, the dotted grey line ($ m_{\textrm{a}} = 2m_{\chi} $) separating on-shell and off-shell productions for the lower plot.
png pdf	Figure 8-b: Observed and expected upper limits at 95% CL on the signal strength in the $ m_{\textrm{a}} $-$ \tan\beta $ (upper left), $ m_{\textrm{a}} $-$ \sin\theta $ (upper right), and $ m_{\textrm{a}} $-$ m_{\chi} $ (lower) planes. The shaded area bounded by solid black line is excluded, with, the dotted grey line ($ m_{\textrm{a}} = 2m_{\chi} $) separating on-shell and off-shell productions for the lower plot.
png pdf	Figure 8-c: Observed and expected upper limits at 95% CL on the signal strength in the $ m_{\textrm{a}} $-$ \tan\beta $ (upper left), $ m_{\textrm{a}} $-$ \sin\theta $ (upper right), and $ m_{\textrm{a}} $-$ m_{\chi} $ (lower) planes. The shaded area bounded by solid black line is excluded, with, the dotted grey line ($ m_{\textrm{a}} = 2m_{\chi} $) separating on-shell and off-shell productions for the lower plot.

Tables
png pdf	Table 1: Preselection criteria applied to all the events entering the SRs and CRs.
png pdf	Table 2: Systematic uncertainties affecting the shape and normalization ($ \ln N$) of the signal and background predictions with an impact greater than 0.5%.

Summary

A search for dark matter produced in association with a pair of bottom quarks is performed using data collected by the CMS detector in 2016--2018, corresponding to an integrated luminosity of 138 fb$ ^{-1} $. The analysis searches for a possible signal by using two independent categories with different multiplicities of jets reconstructed as originating from a bottom quark. The results are interpreted in the framework of a simplified model, namely a type-II two-Higgs-doublet model with an additional pseudoscalar singlet (2HDM+a). It is the first search at the LHC to probe dark matter (DM) produced in association with two nonresonant bottom quarks in this model. This search performs best in the high-$ \tan\beta $ phase space, where the signal production cross section is enhanced. This provides a complementary search to constrain the 2HDM+a model parameter phase space in the region where other DM searches are less sensitive. The lighter pseudoscalar mass below 260 GeV is excluded at 95% confidence level for $ \tan\beta= $ 35, $ \sin\theta= $ 0.7, and $ m_{\textrm{A}}= $ 600 GeV.

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