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| CMS-EXO-18-010 ; CERN-EP-2018-311 | ||
| 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 | ||
| 6 January 2019 | ||
| JHEP 03 (2019) 141 | ||
| Abstract: A search for dark matter produced in association with top quarks in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. The data set used corresponds to an integrated luminosity of 35.9 fb$^{-1}$ recorded with the CMS detector at the LHC. Whereas previous searches for neutral scalar or pseudoscalar mediators considered dark matter production in association with a top quark pair only, this analysis also includes production modes with a single top quark. The results are derived from the combination of multiple selection categories that are defined to target either the single top quark or the top quark pair signature. 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 a scalar or pseudoscalar mediator particle couples to a top quark and subsequently decays into dark matter particles. Scalar and pseudoscalar mediator particles with masses below 290 and 300 GeV, respectively, are excluded at 95% confidence level, assuming a dark matter particle mass of 1 GeV and mediator couplings to fermions and dark matter particles equal to unity. | ||
| Links: e-print arXiv:1901.01553 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Principal production diagrams for the associated production at the LHC of dark matter with a top quark pair (upper left) or a single top quark with associated $t$ channel W boson production (upper right) or with associated tW production (lower left and right). |
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Figure 1-a:
Production diagram for the associated production at the LHC of dark matter with a top quark pair. |
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Figure 1-b:
Production diagram for the associated production at the LHC of dark matter with a single top quark with associated $t$ channel W boson production. |
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Figure 1-c:
Production diagram for the associated production at the LHC of dark matter with associated tW production. |
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Figure 1-d:
Production diagram for the associated production at the LHC of dark matter with associated tW production. |
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Figure 2:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distributions for the CRs of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panels, and the ratio of pre-fit total background to post-fit total background in the middle panels. The lower panels show the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 2-a:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1$\mu$, W CR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 2-b:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1e, W CR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 2-c:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1e, 1$\mu$, top CR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 2-d:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 2e, top CR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 2-e:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 2$\mu$, top CR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 3:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distributions for the CRs of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panels, and the ratio of pre-fit total background to post-fit total background in the middle panels. The lower panels show the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 3-a:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1$\mu$, top CR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 3-b:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1e, top CR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 3-c:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1e, W CR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 3-d:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1$\mu$, W CR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 3-e:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 2e, Z CR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 3-f:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 2$\mu$, Z CR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is negligible and therefore is not shown. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 4:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distributions for the SRs of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panels, and the ratio of pre-fit total background to post-fit total background in the middle panels. The lower panels show the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 4-a:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1e, 0FJ SR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 4-b:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1$\mu$, 0FJ SR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
png pdf |
Figure 4-c:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1$\mu$, 1FJ SR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 4-d:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1e, 1FJ SR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 4-e:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1e, 2 b tag SR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
png pdf |
Figure 4-f:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 1$\mu$, 2 b tag SR of the SL selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
png pdf |
Figure 5:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distributions for the SRs of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panels, and the ratio of pre-fit total background to post-fit total background in the middle panels. The lower panels show the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 5-a:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 0$\ell$, 0FJ SR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 5-b:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 0$\ell$, 1FJ SR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
png pdf |
Figure 5-c:
Background-only post-fit ${{p_{\mathrm {T}}} ^\text {miss}}$ distribution for the 0$\ell$, 2 b tag SR of the AH selection. The total theory signal (${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM and ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM summed together) is presented by the red solid lines for a scalar mediator mass of 100 GeV. The last bin contains overflow events. The dashed magenta lines show the total pre-fit background expectation in the upper panel, and the ratio of pre-fit total background to post-fit total background in the middle panel. The lower panel shows the difference between observed and post-fit total background divided by the full statistical and systematic uncertainties. |
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Figure 6:
The expected and observed 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 for the ${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM signal alone is depicted by the blue dash-dotted line, while the ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM limit alone is given by the red dash-dotted line. The observed limit on the sum of both signals is shown by the black solid line, while the expected value is shown by the black dashed line with the 68 and 95% CL uncertainty bands in green and yellow, respectively. The solid horizontal line corresponds to $\sigma/\sigma_{th}=$ 1. |
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Figure 6-a:
The expected and observed 95% CL limits on the DM production cross sections, relative to the theory predictions, shown for the scalar model. The expected limit for the ${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM signal alone is depicted by the blue dash-dotted line, while the ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM limit alone is given by the red dash-dotted line. The observed limit on the sum of both signals is shown by the black solid line, while the expected value is shown by the black dashed line with the 68 and 95% CL uncertainty bands in green and yellow, respectively. The solid horizontal line corresponds to $\sigma/\sigma_{th}=$ 1. |
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Figure 6-b:
The expected and observed 95% CL limits on the DM production cross sections, relative to the theory predictions, shown for the pseudoscalar model. The expected limit for the ${{{\mathrm {t}}}/\overline {{{\mathrm {t}}}}}$+DM signal alone is depicted by the blue dash-dotted line, while the ${{{\mathrm {t}\overline {\mathrm {t}}}}}$+DM limit alone is given by the red dash-dotted line. The observed limit on the sum of both signals is shown by the black solid line, while the expected value is shown by the black dashed line with the 68 and 95% CL uncertainty bands in green and yellow, respectively. The solid horizontal line corresponds to $\sigma/\sigma_{th}=$ 1. |
| Tables | |
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Table 1:
Final event selections for the SL and AH SRs. Electrons and muons are kept separate for the SL channel. |
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Table 2:
Control regions defined for the main backgrounds of the SL SRs (first two columns, ${{{\mathrm {t}\overline {\mathrm {t}}}} (2\ell)}$ and W+jets) and the AH SRs (last 3 columns, ${{{\mathrm {t}\overline {\mathrm {t}}}} (1\ell)}$, W+jets, and ${{{\mathrm {Z}}} \to \ell \ell}$). Some selections applied in the SRs are removed in the corresponding CRs to increase the available statistics and are therefore not listed. The ${{p_{\mathrm {T}}} ^\text {miss}}$ selection for the ${{{\mathrm {Z}}} \to \ell \ell}$ CR refers to the hadronic recoil. |
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Table 3:
Upper limits at 95% CL on the cross section ratio with respect to the expected DM signal for different scalar ($\phi $) or pseudoscalar (a) mediator masses, $ {{m}_{\chi}} = $ 1 GeV, and $g_{\chi}=g_{{\mathrm {q}}}=$ 1 for the combination of SL and AH signal regions. The median expected value and its 68 and 95% confidence intervals (CIs) are given. |
| Summary |
| The first search at the LHC 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 35.9 fb$^{-1}$ recorded by the CMS experiment in 2016. No significant deviations with respect to standard model predictions are observed and 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 290 and 300 GeV are excluded at 95% confidence level assuming a DM particle mass of 1 GeV and mediator couplings to fermions and DM particles equal to unity. |
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