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| CMS-PAS-EXO-18-010 | ||
| Search for dark matter produced in association with a single top quark or a top quark pair | ||
| CMS Collaboration | ||
| July 2018 | ||
| Abstract: A search for dark matter produced in association with top quarks in proton-proton collisions at a center-of-mass energy of $\sqrt{s}= $ 13 TeV is presented. The dataset used corresponds to an integrated luminosity of 35.9 fb$^{-1}$ recorded with the CMS detector at the LHC. Whereas previous searches for scalar or pseudoscalar interactions 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 a statistical combination of the contributions from multiple signal regions that are defined to target either the single top or top quark pair final states. No significant deviations with respect to standard model predictions are observed. The results are interpreted in the context of simplified models where a new scalar or pseudoscalar mediator particle couples to the top quark and subsequently decays into dark matter particles. Masses below 290 GeV and 300 GeV are excluded at 95% confidence level for scalar and pseudoscalar mediator particles respectively, assuming a dark matter mass of 1 GeV and mediator couplings to fermions and dark matter particles equal to unity. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 03 (2019) 141. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Main production diagrams for the associated production of dark matter with a top quark pair (a) or a single top quark at the LHC: t-channel W boson production (b), and associated tW production (c). |
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Figure 1-a:
Main production diagrams for the associated production of dark matter with a top quark pair (a) or a single top quark at the LHC: t-channel W boson production (b), and associated tW production (c). |
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Figure 1-b:
Main production diagrams for the associated production of dark matter with a top quark pair (a) or a single top quark at the LHC: t-channel W boson production (b), and associated tW production (c). |
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Figure 1-c:
Main production diagrams for the associated production of dark matter with a top quark pair (a) or a single top quark at the LHC: t-channel W boson production (b), and associated tW production (c). |
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Figure 1-d:
Main production diagrams for the associated production of dark matter with a top quark pair (a) or a single top quark at the LHC: t-channel W boson production (b), and associated tW production (c). |
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Figure 2:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the SL selection. The dashed magenta line shows 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 uncertainty. |
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Figure 2-a:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the SL selection. The dashed magenta line shows 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 uncertainty. |
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Figure 2-b:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the SL selection. The dashed magenta line shows 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 uncertainty. |
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Figure 2-c:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the SL selection. The dashed magenta line shows 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 uncertainty. |
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Figure 2-d:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the SL selection. The dashed magenta line shows 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 uncertainty. |
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Figure 2-e:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the SL selection. The dashed magenta line shows 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 uncertainty. |
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Figure 2-f:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the SL selection. The dashed magenta line shows 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 uncertainty. |
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Figure 3:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the AH selection. The dashed magenta line shows 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 uncertainty. |
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Figure 3-a:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the AH selection. The dashed magenta line shows 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 uncertainty. |
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Figure 3-b:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the AH selection. The dashed magenta line shows 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 uncertainty. |
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Figure 3-c:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the SR of the AH selection. The dashed magenta line shows 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 uncertainty. |
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Figure 4:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the SL selection. The dashed magenta line shows 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 uncertainty. |
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Figure 4-a:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the SL selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 4-b:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the SL selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 4-c:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the SL selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 4-d:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the SL selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 4-e:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the SL selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 5:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the AH selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 5-a:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the AH selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 5-b:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the AH selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 5-c:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the AH selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 5-d:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the AH selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 5-e:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the AH selection. The dashed magenta line shows 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 uncertainty. |
png pdf |
Figure 5-f:
Background-only post-fit $ {{p_{\mathrm {T}}} ^\text {miss}} $ distributions for the CR of the AH selection. The dashed magenta line shows 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 uncertainty. |
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Figure 6:
Expected and observed limits: The figures show the expected limits for the scalar (left) and pseudoscalar (right) models. The expected limit for the $ \mathrm{ t/\bar{t} } $+DM signal alone is depicted by the blue dash-dotted line, while the $ \mathrm{ t/\bar{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 expected $\pm$1$ \sigma $ and $ \pm$2$ \sigma $ uncertainty bands in green and yellow, respectively. |
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Figure 6-a:
Expected and observed limits: The figures show the expected limits for the scalar (left) and pseudoscalar (right) models. The expected limit for the $ \mathrm{ t/\bar{t} } $+DM signal alone is depicted by the blue dash-dotted line, while the $ \mathrm{ t/\bar{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 expected $\pm$1$ \sigma $ and $ \pm$2$ \sigma $ uncertainty bands in green and yellow, respectively. |
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Figure 6-b:
Expected and observed limits: The figures show the expected limits for the scalar (left) and pseudoscalar (right) models. The expected limit for the $ \mathrm{ t/\bar{t} } $+DM signal alone is depicted by the blue dash-dotted line, while the $ \mathrm{ t/\bar{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 expected $\pm$1$ \sigma $ and $ \pm$2$ \sigma $ uncertainty bands in green and yellow, respectively. |
| Tables | |
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Table 1:
Final event selection for the SL and AH signal regions. Electrons and muons are kept separate for the SL channel, and two specific regions are defined for the $ \mathrm{ t/\bar{t} } $+DM signal (i.e. $ {n_{{\mathrm {b}}}} =$ 1 and $ {n_{{\mathrm {b}}}} =$ 0 or $\geq $1 forward jets) and for the $ \mathrm{ t/\bar{t} } $+DM signal (i.e. ${n_{{\mathrm {b}}}} \geq $2). |
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Table 2:
Control region definitions for the main backgrounds of the SL signal region (first two columns, $ \mathrm{ t/\bar{t} } (2\ell) $ and W+jets) and the AH signal region (last 3 columns, $ \mathrm{ t/\bar{t} } (1\ell) $, W+jets, and ${\text {Z} \rightarrow \ell \ell}$). |
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Table 3:
Upper limits at 95% confidence level on the cross section ratio with respect to the expected new physics signal for different \textbf {scalar mediator} masses, $\text {m}_{\chi} = $ 1 GeV, and $g_{\chi}=g_{\mathrm {q}}= $ 1 for the combination of AH and SL signal regions. The median and expected $\pm $1$\sigma $, and $\pm $2$\sigma $ values are given. |
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Table 4:
Upper limits at 95% confidence level on the cross section ratio with respect to the expected new physics signal for different \textbf {pseudoscalar mediator} masses, $\text {m}_{\chi} = $ 1 GeV, and $g_{\chi}=g_{\mathrm {q}}=$ 1 for the combination of AH and SL signal regions. The median and expected $\pm $1$\sigma $, and $\pm $2$\sigma $ values are given. |
| Summary |
| The first search at the LHC for dark matter produced in association with a single top quark or a top quark pair in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=$13 TeV has been presented. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$ recorded by the CMS detector at the LHC. No significant deviations with respect to standard model predictions are observed and the results are interpreted in the context of simplified models where a new scalar or pseudoscalar mediator particle couples to the top quark and subsequently decays into two dark matter particles. For masses of the mediator particle below 200 GeV for the scalar model and below 300 GeV for the pseudoscalar model, the leading contribution to the sensitivity of the analysis stems from $ \mathrm{ t\bar{t} } $+DM. This behavior is mostly driven by the larger cross section for $ \mathrm{ t\bar{t} } $+DM when compared to the sum of the production diagrams for $ \mathrm{ t/\bar{t} } $+DM. However, the $ \mathrm{ t/\bar{t} } $+DM cross section drops less rapidly as a function of mediator particle mass in comparison to the $ \mathrm{ t\bar{t} } $+DM mode. Additionally, the $p_{\mathrm{T}}^{\text{miss}} $ spectrum for a given mediator mass leans towards higher values for the $ \mathrm{ t/\bar{t} } $+DM signal model when compared to the $ \mathrm{ t\bar{t} } $+DM model. These two features, together with the analysis specifically designed for both DM production modes and the statistical combination of the different signal regions, lead to up to a factor of two improvement at high mediator masses on the limits when compared to previous results [16]. Scalar and pseudoscalar mediator masses below 290 and 300 GeV are excluded at 95% confidence level. This analysis provides the most stringent limits derived at the LHC for these new spin-0 mediator particles. |
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