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| CMS-TOP-17-019 ; CERN-EP-2019-098 | ||
| Search for the production of four top quarks in the single-lepton and opposite-sign dilepton final states in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 7 June 2019 | ||
| JHEP 11 (2019) 082 | ||
| Abstract: A search for the standard model production of four top quarks (${\mathrm{p}}{\mathrm{p}}\to \mathrm{ t \bar{t} }\mathrm{ t \bar{t} }$) is reported using single-lepton plus jets and opposite-sign dilepton plus jets signatures. Proton-proton collisions are recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV in a sample corresponding to an integrated luminosity of 35.8 fb$^{-1}$. A multivariate analysis exploiting global event and jet properties is used to discriminate $\mathrm{ t \bar{t} }\mathrm{ t \bar{t} }$ from $\mathrm{t\bar{t}}$ production. No significant deviation is observed from the predicted background. An upper limit is set on the cross section for $\mathrm{ t \bar{t} }\mathrm{ t \bar{t} }$ production in the standard model of 48 fb at 95% confidence level. When combined with a previous measurement by the CMS experiment from an analysis of other final states, the observed signal significance is 1.4 standard deviations, and the combined cross section measurement is 13$^{+11}_{-\,9}$ fb. The result is also interpreted in the framework of effective field theory. | ||
| Links: e-print arXiv:1906.02805 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Representative Feynman diagrams for ${\mathrm{p}} {\mathrm{p}} \to {\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}} $ production at lowest order in the SM. |
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Figure 1-a:
Representative Feynman diagram for ${\mathrm{p}} {\mathrm{p}} \to {\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}} $ production at lowest order in the SM. |
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Figure 1-b:
Representative Feynman diagram for ${\mathrm{p}} {\mathrm{p}} \to {\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}} $ production at lowest order in the SM. |
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Figure 2:
Distributions of ${N_{\mathrm {j}}}$, ${N_{\text {tags}}^{\text {m}}}$, ${{p_{\mathrm {T}}} ^{\ell 1}}$ and ${T_{\text {trijet2}}}$ in the combined single-lepton channels. In the upper panels, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panels a relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainties in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. See Section 4.2 for the definitions of the variables. |
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Figure 2-a:
Distribution of ${N_{\mathrm {j}}}$ in the combined single-lepton channels. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel a relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainties in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. |
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Figure 2-b:
Distribution of ${N_{\text {tags}}^{\text {m}}}$ in the combined single-lepton channels. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel a relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainties in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. |
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Figure 2-c:
Distribution of ${{p_{\mathrm {T}}} ^{\ell 1}}$ in the combined single-lepton channels. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel a relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainties in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. |
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Figure 2-d:
Distribution of ${T_{\text {trijet2}}}$ in the combined single-lepton channels. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel a relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainties in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. |
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Figure 3:
Distributions of ${H_{\mathrm {T}}}$, ${{H_{\mathrm {T}}} ^{{\mathrm{b}}}}$, ${H_{\mathrm {T}}^{\mathrm {x}}}$ and ${M_{\text {red}}^{\text {h}}}$ in the combined single-lepton channel. In the upper panels, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panels the relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainty in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. See Section 4.2 for the definitions of the variables. |
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Figure 3-a:
Distribution of ${H_{\mathrm {T}}}$ in the combined single-lepton channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainty in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. |
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Figure 3-b:
Distribution of ${{H_{\mathrm {T}}} ^{{\mathrm{b}}}}$ in the combined single-lepton channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainty in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. |
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Figure 3-c:
Distribution of ${H_{\mathrm {T}}^{\mathrm {x}}}$ in the combined single-lepton channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainty in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. |
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Figure 3-d:
Distribution of ${M_{\text {red}}^{\text {h}}}$ in the combined single-lepton channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to the MC prediction is also shown. In each panel, the shaded band represents the total systematic and statistical uncertainty in the ${\mathrm{t} {}\mathrm{\bar{t}}}$ simulation added in quadrature. |
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Figure 4:
Distributions of ${N_{\mathrm {j}}}$ and ${T_{\text {trijet1}}}$ in the $\mu^{+} {}\mu^{-} $ (upper row) and $\mu^{\pm} \mathrm{e^{\mp}} $ (lower row) channels. In the upper panels of each figure, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panels the relative difference of the data with respect to MC prediction is also shown. In each panel, the shaded band represents the total uncertainty in the dominant ${\mathrm{t} {}\mathrm{\bar{t}}}$ background estimate. See Section 4.2 for the definitions of the variables. |
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Figure 4-a:
Distributions of ${N_{\mathrm {j}}}$ in the $\mu^{+} {}\mu^{-} $ channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to MC prediction is also shown. In each panel, the shaded band represents the total uncertainty in the dominant ${\mathrm{t} {}\mathrm{\bar{t}}}$ background estimate. |
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Figure 4-b:
Distributions of ${T_{\text {trijet1}}}$ in the $\mu^{+} {}\mu^{-} $ channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to MC prediction is also shown. In each panel, the shaded band represents the total uncertainty in the dominant ${\mathrm{t} {}\mathrm{\bar{t}}}$ background estimate. |
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Figure 4-c:
Distributions of ${N_{\mathrm {j}}}$ in the $\mu^{\pm} \mathrm{e^{\mp}} $ channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to MC prediction is also shown. In each panel, the shaded band represents the total uncertainty in the dominant ${\mathrm{t} {}\mathrm{\bar{t}}}$ background estimate. |
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Figure 4-d:
Distributions of ${T_{\text {trijet1}}}$ in the $\mu^{\pm} \mathrm{e^{\mp}} $ channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to MC prediction is also shown. In each panel, the shaded band represents the total uncertainty in the dominant ${\mathrm{t} {}\mathrm{\bar{t}}}$ background estimate. |
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Figure 5:
Distributions of ${N_{\mathrm {j}}}$ and ${T_{\text {trijet1}}}$ in the $\mathrm{e^{+}} {}\mathrm{e^{-}} $ channel. In the upper panels of each figure, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panels the relative difference of the data with respect to MC prediction is also shown. In each panel, the shaded band represents the total uncertainty in the dominant ${\mathrm{t} {}\mathrm{\bar{t}}}$ background estimate. See Section 4.2 for the definitions of the variables. |
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Figure 5-a:
Distribution of ${N_{\mathrm {j}}}$ in the $\mathrm{e^{+}} {}\mathrm{e^{-}} $ channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to MC prediction is also shown. In each panel, the shaded band represents the total uncertainty in the dominant ${\mathrm{t} {}\mathrm{\bar{t}}}$ background estimate. |
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Figure 5-b:
Distribution of ${T_{\text {trijet1}}}$ in the $\mathrm{e^{+}} {}\mathrm{e^{-}} $ channel. In the upper panel, the data are shown as dots with error bars representing statistical uncertainties, MC simulations are shown as a histogram. In the lower panel the relative difference of the data with respect to MC prediction is also shown. In each panel, the shaded band represents the total uncertainty in the dominant ${\mathrm{t} {}\mathrm{\bar{t}}}$ background estimate. |
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Figure 6:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the single-muon channel for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} =$ 7, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 7:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the (upper row) single-muon and (lower row) single-electron channels for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} =$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 7-a:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the single-muon channel for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} =$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 7-b:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the single-electron channel for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} =$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 8:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the (upper row) single-muon and (lower row) single-electron channels for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} =$ 9, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 8-a:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the single-muon channel for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} =$ 9, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 8-b:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the single-electron channel for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} =$ 9, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 9:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the (upper row) single-muon and (lower row) single-electron channels for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} \geq$ 10, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 9-a:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the single-muon channel for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} \geq$ 10, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 9-b:
Post-fit ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ distribution in the single-electron channel for events satisfying baseline single-lepton selection and $ {N_{\mathrm {j}}} \geq$ 10, $ {N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq $4. Non-uniform binning of the BDT discriminant was chosen to achieve approximately uniform distribution of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 10:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distributions in the $\mu^{+} {}\mu^{-} $ channel for events satisfying baseline opposite-sign dilepton selection and (upper row) $ {N_{\mathrm {j}}} =$ 4-5, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3, $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} =$ 2 and (lower row) $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} \geq$ 3, $ {N_{\mathrm {j}}} \geq$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 10-a:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distribution in the $\mu^{+} {}\mu^{-} $ channel for events satisfying baseline opposite-sign dilepton selection and $ {N_{\mathrm {j}}} =$ 4-5, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3, $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} =$ 2. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 10-b:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distribution in the $\mu^{+} {}\mu^{-} $ channel for events satisfying baseline opposite-sign dilepton selection and $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} \geq$ 3, $ {N_{\mathrm {j}}} \geq$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 11:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distributions in the $\mu^{\pm} \mathrm{e^{\mp}} $ channel for events satisfying baseline opposite-sign dilepton selection and (upper row) $ {N_{\mathrm {j}}} =$ 4-5, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3, $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} =$ 2 and (lower row) $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} \geq$ 3, $ {N_{\mathrm {j}}} \geq$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 11-a:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distribution in the $\mu^{\pm} \mathrm{e^{\mp}} $ channel for events satisfying baseline opposite-sign dilepton selection and $ {N_{\mathrm {j}}} =$ 4-5, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3, $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} =$ 2. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 11-b:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distribution in the $\mu^{\pm} \mathrm{e^{\mp}} $ channel for events satisfying baseline opposite-sign dilepton selection and $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} \geq$ 3, $ {N_{\mathrm {j}}} \geq$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 12:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distributions in the $\mathrm{e^{+}} {}\mathrm{e^{-}} $ channel for events satisfying baseline opposite-sign dilepton selection and (upper row) $ {N_{\mathrm {j}}} =$ 4-5, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3, $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} =$ 2 and (lower row) $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} \geq$ 3, $ {N_{\mathrm {j}}} \geq$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 12-a:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distribution in the $\mathrm{e^{+}} {}\mathrm{e^{-}} $ channel for events satisfying baseline opposite-sign dilepton selection and $ {N_{\mathrm {j}}} =$ 4-5, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3, $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} =$ 2. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
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Figure 12-b:
Post-fit $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ distribution in the $\mathrm{e^{+}} {}\mathrm{e^{-}} $ channel for events satisfying baseline opposite-sign dilepton selection and $ {N_{\mathrm {j}}} =$ 6-7, $ {N_{\text {tags}}^{\text {m}}} \geq$ 3, $ {N_{\mathrm {j}}} \geq$ 8, $ {N_{\text {tags}}^{\text {m}}} =$ 2, $\geq $3. Dots represent data. Vertical error bars show the statistical uncertainties in data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty in the total background and are centered around the pre-fit expectation value of the prediction. The hatched area shows the size of the post-fit uncertainty in the background prediction. The signal histogram template is shown as a solid line. The lower panel shows the relative difference of the observed number of events over the post-fit background prediction. |
| Tables | |
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Table 1:
Uncertainties that affect the normalization of the data sets and shapes of the ${D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SL}}}$ and $ {D_{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {DL}}}$ discriminants. Their contribution to different effects are marked by X. |
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Table 2:
Maximum-likelihood signal strength and cross section estimates, as well as the expected and observed significance of SM $ {\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}$ production. The results for the two analyses from this paper are shown separately and combined. The results from a previous CMS multilepton measurement are also given [15]. The values quoted for the uncertainties on the signal strengths and cross sections are the one standard deviation (s.d.) values and include all statistical and systematic uncertainties. The expected significance is calculated assuming that the data are distributed according to the prediction of the SM with nominal $ {\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}$ production cross section value $\sigma _{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^\text {SM}$, which corresponds to the assumed signal strength modifier value $\mu =$ 1. |
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Table 3:
Expected and observed 95% CL upper limits on SM $ {\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}$ production as a multiple of ${\sigma _{{\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}}^{\text {SM}}}$ and in fb. The results for the two analyses from this paper are shown separately and combined. The results from a previous CMS multilepton search are also given [15]. The values quoted for the uncertainties in the expected limits indicate the regions containing 68% of the distribution of limits expected under the background-only hypothesis. The expected upper limits are calculated assuming that the data are distributed according to the prediction of the background-only model corresponding to the scenario with signal strength modifier value $\mu =$ 0. |
png pdf |
Table 4:
Linear (left) and quadratic (right) parameterization coefficients, $\sigma _{k}^{\left (1\right)}$ and $\sigma _{{j},{k}}^{\left (2\right)}$, of Eq. 3. The coefficients $\sigma _{k}^{\left (1\right)}$ are in units (fb TeV$^{2}$), while the coefficients $\sigma _{{j},{k}}^{\left (2\right)}$ are in units (fb TeV$^{4}$). |
png pdf |
Table 5:
Expected and observed 95% CL intervals for selected coupling parameters. The intervals are extracted from upper limit on the $ {\mathrm{t} \mathrm{\bar{t}} \mathrm{t} \mathrm{\bar{t}}}$ production cross section in the EFT model, where only one selected operator has a nonvanishing contribution. |
png pdf |
Table 6:
Expected and observed 95% CL intervals for selected coupling parameters when contribution of other operators is marginalized. |
| Summary |
| A search for standard model ${\mathrm{ t \bar{t} }\mathrm{ t \bar{t} }}$ production has been performed in final states with one or two oppositely signed muons or electrons plus jets. The observed yields attributed to ${\mathrm{ t \bar{t} }\mathrm{ t \bar{t} }}$ production are consistent with the background predictions. An upper limit at 95% confidence level of 48 fb is set on the cross section for ${\mathrm{ t \bar{t} }\mathrm{ t \bar{t} }}$ production. Combining this result with a previous same-sign dilepton and multilepton search [15] the resulting cross section is 13$^{+11}_{-9}$ fb with an observed significance of 1.4 standard deviations. The combined result constitutes one of the most stringent constraints from CMS on the production of four top quarks and can be used for phenomenological reinterpretation of a wide range of new physics models. The experimental results are interpreted in the effective field theory framework and yield limits on dimension-6 four-fermion operators coupling to third generation quarks. |
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