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| CMS-PAS-EXO-22-014 | ||
| Search for dark matter produced in association with a single top quark or a top quark pair in proton-proton collisions at $ \sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 15 April 2024 | ||
| Abstract: A search is performed for dark matter produced in association with top quarks using the data collected by the CMS detector at the LHC from proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to 138 fb$ ^{-1} $ of integrated luminosity. The analysis explores the production of dark matter particles in association with a single top quark or a pair of top quarks. Various decay modes of the top quark are probed, resulting in three separate channels based on the number of leptons in the final state, namely the all-hadronic (zero lepton), semileptonic (one lepton), and the dileptonic (two leptons) final states. The results are derived from the combination of these different categories. The analysis looks for an excess of events with respect to the background-only prescription in events with a large imbalance in the transverse momentum. Novel multivariate techniques are used to take advantage of the differences in kinematics between the two dark matter associated production modes. 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 dark matter fermions. The largest local significance is within 2 standard deviations for all mediator hypotheses. | ||
| Links: CDS record (PDF) ; 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} $) mediator for the associated production of DM particles ($ \chi $) with a top quark pair $ {\mathrm{t}\overline{\mathrm{t}}} $+DM (left) and a single top quark $ {\mathrm{t}}/\overline{{\mathrm{t}}} $+DM in both t-channel (center) and $ \mathrm{t}\mathrm{W} $-channel (right) production modes. Note that the additional quark, $ \mathrm{q} $ in the t-channel diagram, is often produced at high pseudorapidities. |
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Figure 1-a:
Principal production diagrams in the context of the simplified model with a scalar/pseudoscalar ($ \phi/\mathrm{a} $) mediator for the associated production of DM particles ($ \chi $) with a top quark pair $ {\mathrm{t}\overline{\mathrm{t}}} $+DM (left) and a single top quark $ {\mathrm{t}}/\overline{{\mathrm{t}}} $+DM in both t-channel (center) and $ \mathrm{t}\mathrm{W} $-channel (right) production modes. Note that the additional quark, $ \mathrm{q} $ in the t-channel diagram, is often produced at high pseudorapidities. |
png pdf |
Figure 1-b:
Principal production diagrams in the context of the simplified model with a scalar/pseudoscalar ($ \phi/\mathrm{a} $) mediator for the associated production of DM particles ($ \chi $) with a top quark pair $ {\mathrm{t}\overline{\mathrm{t}}} $+DM (left) and a single top quark $ {\mathrm{t}}/\overline{{\mathrm{t}}} $+DM in both t-channel (center) and $ \mathrm{t}\mathrm{W} $-channel (right) production modes. Note that the additional quark, $ \mathrm{q} $ in the t-channel diagram, is often produced at high pseudorapidities. |
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Figure 1-c:
Principal production diagrams in the context of the simplified model with a scalar/pseudoscalar ($ \phi/\mathrm{a} $) mediator for the associated production of DM particles ($ \chi $) with a top quark pair $ {\mathrm{t}\overline{\mathrm{t}}} $+DM (left) and a single top quark $ {\mathrm{t}}/\overline{{\mathrm{t}}} $+DM in both t-channel (center) and $ \mathrm{t}\mathrm{W} $-channel (right) production modes. Note that the additional quark, $ \mathrm{q} $ in the t-channel diagram, is often produced at high pseudorapidities. |
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Figure 2:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the AH channel for the three SRs: 0f (left), 1f (center), and 2b (right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 2-a:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the AH channel for the three SRs: 0f (left), 1f (center), and 2b (right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 2-b:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the AH channel for the three SRs: 0f (left), 1f (center), and 2b (right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
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Figure 2-c:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the AH channel for the three SRs: 0f (left), 1f (center), and 2b (right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
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Figure 3:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the SL channel for the six SRs devised: T1 0f (upper left), T1 1f (upper center), T1 2b (upper right), T2 0f (lower left), T2 1f (lower center), and T2 2b (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 3-a:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the SL channel for the six SRs devised: T1 0f (upper left), T1 1f (upper center), T1 2b (upper right), T2 0f (lower left), T2 1f (lower center), and T2 2b (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 3-b:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the SL channel for the six SRs devised: T1 0f (upper left), T1 1f (upper center), T1 2b (upper right), T2 0f (lower left), T2 1f (lower center), and T2 2b (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 3-c:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the SL channel for the six SRs devised: T1 0f (upper left), T1 1f (upper center), T1 2b (upper right), T2 0f (lower left), T2 1f (lower center), and T2 2b (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 3-d:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the SL channel for the six SRs devised: T1 0f (upper left), T1 1f (upper center), T1 2b (upper right), T2 0f (lower left), T2 1f (lower center), and T2 2b (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 3-e:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the SL channel for the six SRs devised: T1 0f (upper left), T1 1f (upper center), T1 2b (upper right), T2 0f (lower left), T2 1f (lower center), and T2 2b (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 3-f:
The main discriminator distribution ($ p_{\mathrm{T}}^\text{miss} $) employed in the SL channel for the six SRs devised: T1 0f (upper left), T1 1f (upper center), T1 2b (upper right), T2 0f (lower left), T2 1f (lower center), and T2 2b (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 4:
The main discriminator distribution (NN) employed in the DL channel for the four SRs devised: $ {\mathrm{t}\overline{\mathrm{t}}} $+DM OF (upper left), $ {\mathrm{t}\overline{\mathrm{t}}} $+DM SF (upper right), $ \mathrm{t}\mathrm{W} $+DM OF (lower left), and $ \mathrm{t}\mathrm{W} $+DM SF (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 4-a:
The main discriminator distribution (NN) employed in the DL channel for the four SRs devised: $ {\mathrm{t}\overline{\mathrm{t}}} $+DM OF (upper left), $ {\mathrm{t}\overline{\mathrm{t}}} $+DM SF (upper right), $ \mathrm{t}\mathrm{W} $+DM OF (lower left), and $ \mathrm{t}\mathrm{W} $+DM SF (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 4-b:
The main discriminator distribution (NN) employed in the DL channel for the four SRs devised: $ {\mathrm{t}\overline{\mathrm{t}}} $+DM OF (upper left), $ {\mathrm{t}\overline{\mathrm{t}}} $+DM SF (upper right), $ \mathrm{t}\mathrm{W} $+DM OF (lower left), and $ \mathrm{t}\mathrm{W} $+DM SF (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 4-c:
The main discriminator distribution (NN) employed in the DL channel for the four SRs devised: $ {\mathrm{t}\overline{\mathrm{t}}} $+DM OF (upper left), $ {\mathrm{t}\overline{\mathrm{t}}} $+DM SF (upper right), $ \mathrm{t}\mathrm{W} $+DM OF (lower left), and $ \mathrm{t}\mathrm{W} $+DM SF (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 4-d:
The main discriminator distribution (NN) employed in the DL channel for the four SRs devised: $ {\mathrm{t}\overline{\mathrm{t}}} $+DM OF (upper left), $ {\mathrm{t}\overline{\mathrm{t}}} $+DM SF (upper right), $ \mathrm{t}\mathrm{W} $+DM OF (lower left), and $ \mathrm{t}\mathrm{W} $+DM SF (lower right). The last bin contains overflow events. The various background processes are represented with color-filled histograms as indicated in the legend. A representative signal model distribution is also shown. The grey dashed area in the upper panel represents the total post-fit background and one signal hypothesis summed together and their associated statistical and systematic uncertainties. The data points are shown as black dots with vertical and horizontal error bars. The lower panel shows the post-fit values and uncertainties of the ratio between the observed data and the predicted SM background. The figure comprises the total collected data in Run 2. |
png pdf |
Figure 5:
The expected 95% CL limits on the DM production cross sections relative to the theory predictions shown for the scalar (left) and pseudoscalar (right) models. The expected limit on the sum of both signals 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. The solid horizontal line corresponds to $ \sigma/\sigma_{\text{th}}= $ 1. |
png pdf |
Figure 5-a:
The expected 95% CL limits on the DM production cross sections relative to the theory predictions shown for the scalar (left) and pseudoscalar (right) models. The expected limit on the sum of both signals 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. The solid horizontal line corresponds to $ \sigma/\sigma_{\text{th}}= $ 1. |
png pdf |
Figure 5-b:
The expected 95% CL limits on the DM production cross sections relative to the theory predictions shown for the scalar (left) and pseudoscalar (right) models. The expected limit on the sum of both signals 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. The solid horizontal line corresponds to $ \sigma/\sigma_{\text{th}}= $ 1. |
| Tables | |
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Table 1:
Final event selections 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 instead split into same flavour (SF) $ e^{+}e^{-} $/$ \mu^{+}\mu^{-} $ and opposite flavour (OF) $ 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\mathrm{l}) $, W+jets, $ {\mathrm{Z}} \to \mathrm{l} \mathrm{l} $, QCD), the SL SRs (central two columns, $ {\mathrm{t}\overline{\mathrm{t}}} (2\mathrm{l}) $ and W+jets ), and the DL SRs (last 2 columns, $ {\mathrm{t}\overline{\mathrm{t}}} (2\mathrm{l}) $ 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 \mathrm{l} \mathrm{l} $ 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 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 data correspond to an integrated luminosity of 138 fb$ ^{-1} $ recorded by the CMS experiment between 2016 and 2018. Various decay modes of the top quark are probed, resulting in three separate channels based on the number of leptons in the final state, namely the all-hadronic (zero leptons), semileptonic (one lepton), and dileptonic (two leptons) final states. 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 400 and 380 GeV, respectively, are expected to be excluded at 95% confidence level assuming a DM particle mass of 1 GeV and mediator couplings to fermions and DM particles equal to unity. A signal-like excess is observed in data. Because the signal kinematics are not very sensitive to the mass of the mediator, this excess is consistent with all mediator mass hypotheses. The largest excess for all mediator hypotheses is within two standard deviations. Because of this excess, we only exclude mediator masses below 280 (290) GeV for the scalar (pseudoscalar) mediator. |
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Compact Muon Solenoid LHC, CERN |
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