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| CMS-PAS-EXO-16-040 | ||
| Search for new physics in a boosted hadronic monotop final state using 12.9 fb$^{-1}$ of $ \sqrt{s} = $ 13 TeV data | ||
| CMS Collaboration | ||
| August 2016 | ||
| Abstract: A search for dark matter is conducted in events with large missing transverse energy and a hadronically decaying, boosted top quark. This study is performed using proton-proton collision data collected by the CMS detector, corresponding to an integrated luminosity of 12.9 fb$^{-1}$. No significant deviations from standard model predictions are observed, and limits are placed on the production of new heavy bosons coupling to dark matter particles. | ||
| Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1-a:
Example of monotop production via a neutral flavor-changing current (a) and a heavy scalar (b). |
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Figure 1-b:
Example of monotop production via a neutral flavor-changing current (a) and a heavy scalar (b). |
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Figure 2-a:
Comparison between data and Monte Carlo simulation in the control regions before and after performing the simultaneous fit to the different control regions and signal region. Plot (a) corresponds to the dielectron control region, and plot (b) corresponds to the dimuon control region. Plot (c) corresponds to the photon control region. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The stacked histograms show the individual SM background distributions after the fit is performed. The gray band indicates the post-fit uncertainty after propagating all the systematic uncertainties in the fit. |
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Figure 2-b:
Comparison between data and Monte Carlo simulation in the control regions before and after performing the simultaneous fit to the different control regions and signal region. Plot (a) corresponds to the dielectron control region, and plot (b) corresponds to the dimuon control region. Plot (c) corresponds to the photon control region. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The stacked histograms show the individual SM background distributions after the fit is performed. The gray band indicates the post-fit uncertainty after propagating all the systematic uncertainties in the fit. |
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Figure 2-c:
Comparison between data and Monte Carlo simulation in the control regions before and after performing the simultaneous fit to the different control regions and signal region. Plot (a) corresponds to the dielectron control region, and plot (b) corresponds to the dimuon control region. Plot (c) corresponds to the photon control region. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The stacked histograms show the individual SM background distributions after the fit is performed. The gray band indicates the post-fit uncertainty after propagating all the systematic uncertainties in the fit. |
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Figure 3-a:
Comparison between data and Monte Carlo simulation in the control regions before and after performing the simultaneous fit to the different control regions and signal region. Plot (a) corresponds to the single electron anti-$b$-tagged control region and plot (b) corresponds to the single muon anti-$b$-tagged control region. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The stacked histograms show the individual SM background distributions after the fit is performed. The gray band represents the post-fit uncertainty propagating all systematic uncertainties through. |
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Figure 3-b:
Comparison between data and Monte Carlo simulation in the control regions before and after performing the simultaneous fit to the different control regions and signal region. Plot (a) corresponds to the single electron anti-$b$-tagged control region and plot (b) corresponds to the single muon anti-$b$-tagged control region. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The stacked histograms show the individual SM background distributions after the fit is performed. The gray band represents the post-fit uncertainty propagating all systematic uncertainties through. |
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Figure 4-a:
Comparison between data and Monte Carlo simulation in the control regions before and after performing the simultaneous fit to the different control regions and signal region. Plot (a) corresponds to the single electron $b$-tagged control region and plot (b) corresponds to the single muon $b$-tagged control region. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The stacked histograms show the individual SM background distributions after the fit is performed. The gray band represents the post-fit uncertainty propagating all systematic uncertainties through. |
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Figure 4-b:
Comparison between data and Monte Carlo simulation in the control regions before and after performing the simultaneous fit to the different control regions and signal region. Plot (a) corresponds to the single electron $b$-tagged control region and plot (b) corresponds to the single muon $b$-tagged control region. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The stacked histograms show the individual SM background distributions after the fit is performed. The gray band represents the post-fit uncertainty propagating all systematic uncertainties through. |
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Figure 5:
Distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ from SM backgrounds and data in the signal region after simultaneously fitting in the signal region and all control regions. The stacked histograms show the individual SM background distributions after the fit is performed. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The gray bands indicate the post-fit uncertainty on the background, assuming no signal. |
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Figure 6:
Distribution of ${E_{\mathrm {T}}^{\text {miss}}}$ from SM backgrounds and data in the signal region after fitting only in the control regions and propagating the background estimates to the signal region. The stacked histograms show the individual SM background distributions after the fit is performed. The blue solid line represents the sum of the SM background contributions normalized to the post-fit yield. The red solid line represents the sum of the SM background contributions normalized to the theoretical prediction. The gray bands indicate the post-fit uncertainty on the background, assuming no signal. |
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Figure 7-a:
Results assuming a FCNC interpretation of the monotop signature. Shown are upper limits as a function of the mass of the vector field $V$, assuming fixed $a_\text {FC} = b_\text {FC}=$ 0.25 and a dark matter mass of $M_\chi =$ 10 GeV. The limits are placed at a confidence level of 95%. a: limits on the inclusive cross section for monotop production; b: limits on $\sigma /\sigma _\text {theory}$. The green and yellow bands represent 1 and 2 standard deviations of experimental uncertainties, respectively. The red shaded band represents the 20% signal cross-section uncertainty. |
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Figure 7-b:
Results assuming a FCNC interpretation of the monotop signature. Shown are upper limits as a function of the mass of the vector field $V$, assuming fixed $a_\text {FC} = b_\text {FC}=$ 0.25 and a dark matter mass of $M_\chi =$ 10 GeV. The limits are placed at a confidence level of 95%. a: limits on the inclusive cross section for monotop production; b: limits on $\sigma /\sigma _\text {theory}$. The green and yellow bands represent 1 and 2 standard deviations of experimental uncertainties, respectively. The red shaded band represents the 20% signal cross-section uncertainty. |
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Figure 8:
Results for the FCNC interpretation presented in the two-dimensional plane spanned by the mediator and dark matter masses. The observed exclusion range (red solid line) is shown, also for the cases in which the predicted cross section is shifted by the assigned theory uncertainty (red dashed lines). The expected exclusion range is indicated by a black solid line, demonstrating the search sensitivity of the analysis. The experimental uncertainties are shown in black dashed lines. |
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Figure 9-a:
Results assuming a resonant interpretation of the monotop signature. Shown are upper limits as a function of the mass of the scalar particle $S$, assuming fixed $a_\text {SR} = b_\text {SR}= $ 0.1. The limits are placed at a confidence level of 95%. a: limits on the inclusive cross section for monotop production; b: limits on $\sigma /\sigma _\text {theory}$. The green and yellow bands represent 1 and 2 standard deviations of experimental uncertainties, respectively. The red shaded band represents the 20% signal cross-section uncertainty. |
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Figure 9-b:
Results assuming a resonant interpretation of the monotop signature. Shown are upper limits as a function of the mass of the scalar particle $S$, assuming fixed $a_\text {SR} = b_\text {SR}= $ 0.1. The limits are placed at a confidence level of 95%. a: limits on the inclusive cross section for monotop production; b: limits on $\sigma /\sigma _\text {theory}$. The green and yellow bands represent 1 and 2 standard deviations of experimental uncertainties, respectively. The red shaded band represents the 20% signal cross-section uncertainty. |
| Summary |
| A search for dark matter in the monotop final state is performed. The data is found to be in agreement with the Standard Model prediction. Results are interpreted in terms of dark matter particles produced via a neutral flavor-changing interaction or via the decay of a colored, scalar resonance together with a single top quark. For the non-resonant model, assuming $m_\chi = 10 \gev$ and $a_\text{FC}=b_\text{FC}=$ 0.25, flavor-changing neutral currents of $m_V < $ 1.5 TeV are excluded at 95% confidence level, compared to an expected exclusion of $m_V<1.7 TeV$. For the resonant model, scalar fields with $M_\phi < $ 2.7 TeV are excluded at 95% confidence level, compared to an expected exclusion of $m_V < $ 3.0 TeV. This extends the previous limit on the resonant model, which was set at $M_\phi =$ 1.6 TeV [5]. |
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