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| CMS-EXO-22-014 ; CERN-EP-2024-338 | ||
| Search for dark matter produced in association with one or two top quarks in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 24 January 2025 | ||
| Submitted to J. High Energy Phys. | ||
| Abstract: A search is performed for dark matter (DM) produced in association with a single top quark or a pair of top quarks using the data collected with the CMS detector at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to 138 fb$ ^{-1} $ of integrated luminosity. Events are classified into zero-lepton, single-lepton, and two-lepton final states. The results are derived from the combination of these different categories. An excess of events with respect to the background-only prediction is searched for in events with a large imbalance in the transverse momentum. Novel multivariate techniques are used to take advantage of the differences in kinematic properties between the two DM production mechanisms. No significant deviations with respect to the standard model predictions are observed. The results are interpreted in the context of a simplified model in which either a scalar or pseudoscalar mediator couples to top quarks and to DM fermions, as well as for axion-like particles that are coupled to top quarks and DM fermions. Expected exclusion limits of 410 and 380 GeV for scalar and pseudoscalar mediator masses, respectively, are set at the 95% confidence level. A DM particle mass of 1 GeV is assumed, with mediator couplings to fermions and DM particles set to unity. A small signal-like excess is observed in data. Because of this excess, mediator masses are only excluded below 310 (320) GeV for the scalar (pseudoscalar) mediator. The results are also translated into model-independent 95% confidence level upper limits on the visible cross section of DM production in association with top quarks, ranging from 1 pb to 0.02 pb. | ||
| Links: CDS record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Principal production diagrams in the context of the simplified model with a scalar/pseudoscalar ($ \phi/\mathrm{a} $) mediator for the associated production of a pair of DM particles ($ \chi $) with a top quark pair (left) and a single top quark in both $ t $-channel (center), and tW-channel (right) production modes. The additional quark $ \mathrm{q} $ in the $ t $-channel diagram is often produced at high pseudorapidity. |
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Figure 1-a:
Principal production diagrams in the context of the simplified model with a scalar/pseudoscalar ($ \phi/\mathrm{a} $) mediator for the associated production of a pair of DM particles ($ \chi $) with a top quark pair (left) and a single top quark in both $ t $-channel (center), and tW-channel (right) production modes. The additional quark $ \mathrm{q} $ in the $ t $-channel diagram is often produced at high pseudorapidity. |
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Figure 1-b:
Principal production diagrams in the context of the simplified model with a scalar/pseudoscalar ($ \phi/\mathrm{a} $) mediator for the associated production of a pair of DM particles ($ \chi $) with a top quark pair (left) and a single top quark in both $ t $-channel (center), and tW-channel (right) production modes. The additional quark $ \mathrm{q} $ in the $ t $-channel diagram is often produced at high pseudorapidity. |
png pdf |
Figure 1-c:
Principal production diagrams in the context of the simplified model with a scalar/pseudoscalar ($ \phi/\mathrm{a} $) mediator for the associated production of a pair of DM particles ($ \chi $) with a top quark pair (left) and a single top quark in both $ t $-channel (center), and tW-channel (right) production modes. The additional quark $ \mathrm{q} $ in the $ t $-channel diagram is often produced at high pseudorapidity. |
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Figure 2:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the three AH SRs: 1b 0FJ (top left), 1b 1FJ (top right), and 2b (bottom). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 2-a:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the three AH SRs: 1b 0FJ (top left), 1b 1FJ (top right), and 2b (bottom). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 2-b:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the three AH SRs: 1b 0FJ (top left), 1b 1FJ (top right), and 2b (bottom). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 2-c:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the three AH SRs: 1b 0FJ (top left), 1b 1FJ (top right), and 2b (bottom). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 3:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the six SL SRs: 1b 0FJ ($ t \leq $ 0) (top left), 1b 0FJ ($ t > $ 0) (top right), 1b 1FJ ($ t \leq $ 0) (center left), 1b 1FJ ($ t > $ 0) (center right), 2b ($ t \leq $ 0) (bottom left), and 2b ($ t > $ 0) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 3-a:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the six SL SRs: 1b 0FJ ($ t \leq $ 0) (top left), 1b 0FJ ($ t > $ 0) (top right), 1b 1FJ ($ t \leq $ 0) (center left), 1b 1FJ ($ t > $ 0) (center right), 2b ($ t \leq $ 0) (bottom left), and 2b ($ t > $ 0) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 3-b:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the six SL SRs: 1b 0FJ ($ t \leq $ 0) (top left), 1b 0FJ ($ t > $ 0) (top right), 1b 1FJ ($ t \leq $ 0) (center left), 1b 1FJ ($ t > $ 0) (center right), 2b ($ t \leq $ 0) (bottom left), and 2b ($ t > $ 0) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 3-c:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the six SL SRs: 1b 0FJ ($ t \leq $ 0) (top left), 1b 0FJ ($ t > $ 0) (top right), 1b 1FJ ($ t \leq $ 0) (center left), 1b 1FJ ($ t > $ 0) (center right), 2b ($ t \leq $ 0) (bottom left), and 2b ($ t > $ 0) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 3-d:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the six SL SRs: 1b 0FJ ($ t \leq $ 0) (top left), 1b 0FJ ($ t > $ 0) (top right), 1b 1FJ ($ t \leq $ 0) (center left), 1b 1FJ ($ t > $ 0) (center right), 2b ($ t \leq $ 0) (bottom left), and 2b ($ t > $ 0) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 3-e:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the six SL SRs: 1b 0FJ ($ t \leq $ 0) (top left), 1b 0FJ ($ t > $ 0) (top right), 1b 1FJ ($ t \leq $ 0) (center left), 1b 1FJ ($ t > $ 0) (center right), 2b ($ t \leq $ 0) (bottom left), and 2b ($ t > $ 0) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 3-f:
The main discriminant distribution $ p_{\mathrm{T}}^\text{miss} $ in the six SL SRs: 1b 0FJ ($ t \leq $ 0) (top left), 1b 0FJ ($ t > $ 0) (top right), 1b 1FJ ($ t \leq $ 0) (center left), 1b 1FJ ($ t > $ 0) (center right), 2b ($ t \leq $ 0) (bottom left), and 2b ($ t > $ 0) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 4:
The main discriminant distribution NN in the the four DL SRs: 2b (DF) (top left), 2b (SF) (top right), 1b (DF) (bottom left), and 1b (SF) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 4-a:
The main discriminant distribution NN in the the four DL SRs: 2b (DF) (top left), 2b (SF) (top right), 1b (DF) (bottom left), and 1b (SF) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 4-b:
The main discriminant distribution NN in the the four DL SRs: 2b (DF) (top left), 2b (SF) (top right), 1b (DF) (bottom left), and 1b (SF) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 4-c:
The main discriminant distribution NN in the the four DL SRs: 2b (DF) (top left), 2b (SF) (top right), 1b (DF) (bottom left), and 1b (SF) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 4-d:
The main discriminant distribution NN in the the four DL SRs: 2b (DF) (top left), 2b (SF) (top right), 1b (DF) (bottom left), and 1b (SF) (bottom right). The solid histograms for the simulated SM backgrounds are summed cumulatively and rescaled to luminosity and the grey dashed band represents the associated statistical uncertainty. The data are represented by solid points with the horizontal bar indicates the width of the bin and the vertical one the associated statistical uncertainty. A representative signal model distribution is also shown. The last bin contains overflow events. In the lower plots the ratio between data and the total SM background after the simultaneous fit is presented with the total associated uncertainty. |
png pdf |
Figure 5:
The model-independent 95% CL limits on production cross section for new physics processes for the scalar (left) and pseudoscalar (right) interactions. The expected limit is shown by the black dashed line with the 68 and 95% CL uncertainty bands in green and yellow, respectively, while the observed limit is shown by the solid black line. Theoretical LO cross section values for the DM model and their associated uncertainties are also presented (grey line). |
png pdf |
Figure 5-a:
The model-independent 95% CL limits on production cross section for new physics processes for the scalar (left) and pseudoscalar (right) interactions. The expected limit is shown by the black dashed line with the 68 and 95% CL uncertainty bands in green and yellow, respectively, while the observed limit is shown by the solid black line. Theoretical LO cross section values for the DM model and their associated uncertainties are also presented (grey line). |
png pdf |
Figure 5-b:
The model-independent 95% CL limits on production cross section for new physics processes for the scalar (left) and pseudoscalar (right) interactions. The expected limit is shown by the black dashed line with the 68 and 95% CL uncertainty bands in green and yellow, respectively, while the observed limit is shown by the solid black line. Theoretical LO cross section values for the DM model and their associated uncertainties are also presented (grey line). |
png pdf |
Figure 6:
The 95% CL limits on the ratio of ALP-top coupling to the ALP decay constant ($ |c_{\mathrm{t}}|/f_{\mathrm{A}} $) as a function of mediator mass for the ALP mediator model. The expected limit is shown by the black dashed line with the 68 and 95% CL uncertainty bands in green and yellow, respectively, whereas the observed limit is shown by the solid black line. |
| Tables | |
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Table 1:
Final event selection requirements for the AH, SL, and DL SRs. For the SL channel, a categorization in terms of modified topness, with bins of $ t\leq $ 0 and $ t > $ 0, is also applied after the event selection. The DL channel is split into SF $ \mathrm{e}^{+}\mathrm{e}^{-} $/$ \mu^{+}\mu^{-} $ and DF $ \mathrm{e}^{\pm}\mu^{\mp} $ regions. |
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Table 2:
CRs defined for the main backgrounds of the AH SRs (first 4 columns, $ {\mathrm{t}\overline{\mathrm{t}}} (1\ell) $, W+jets, $ {\mathrm{Z}} \to \ell \bar{\ell} $, QCD), the SL SRs (central two columns, $ {\mathrm{t}\overline{\mathrm{t}}} (2\ell) $ and W+jets ), and the DL SRs (last 2 columns, $ {\mathrm{t}\overline{\mathrm{t}}} (2\ell) $ and $ {\mathrm{t}\overline{\mathrm{t}}} \mathrm{Z} $). Some selection criteria applied in the SRs are removed in the corresponding CRs to increase the event counts and are therefore not listed. The $ p_{\mathrm{T}}^\text{miss} $ selection for the $ {\mathrm{Z}} \to \ell \bar{\ell} $ CR refers to the hadronic recoil. |
| Summary |
| A search for dark matter (DM) produced in association with a single top quark or a top quark pair produced in interactions mediated by a neutral scalar or pseudoscalar particle in proton-proton collisions at a center-of-mass energy of 13 TeV has been presented. The search was performed using data corresponding to an integrated luminosity of 138 fb$ ^{-1} $ recorded by the CMS experiment between 2016 and 2018. For the first time, events are classified into zero lepton, single-lepton, and two lepton final states. In addition, a different phase space was explored with respect to the best LHC results looking for DM produced in association with a top quark pair. In particular, lower jet multiplicities were considered, which results in an increase in the sensitivity to processes where DM is produced in association with a single top quark. The results are interpreted in the context of a simplified model in which a scalar or pseudoscalar mediator particle couples to the top quark and subsequently decays into two DM particles. Scalar and pseudoscalar mediator masses below 410 and 380 GeV, respectively, are expected to be excluded at 95% confidence level (CL) assuming a DM particle mass of 1 GeV and mediator couplings to fermions and DM particles equal to unity. This work extends the sensitivity for the DM mediator mass when produced in association with one or two top quarks by up to 10% with respect to the LHC combination across all channels using Run 2 data, and by up to 40% with respect to the best LHC result with 2016 data. Of these improvements, up to 20% come from the introduction of analysis improvements and the dileptonic final state. A small signal-like excess is observed in data. Because the signal kinematic properties do not significantly depend on the mass of the mediator, this excess is consistent with all mediator mass hypotheses. The largest local significance for all mediator hypotheses is observed to be within two standard deviations. Because of this excess, mediator masses are only excluded below 310 (320) GeV for the scalar (pseudoscalar) mediator. The results are also translated into model-independent 95% CL upper limits on the visible cross section of DM production in association with top quarks, ranging from 1 pb to 0.02 pb. In addition, limits on the coupling of axion-like-particles (ALP) to top quarks are set for the first time. This is performed in the context of top quark(s) plus invisible signatures where the ALP couples to SM quarks as a mediator between the SM and fermionic DM particles. |
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