CMS-PAS-TOP-17-019 | ||
Search for standard model production of four top quarks with the single-lepton and opposite-sign dilepton final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV | ||
CMS Collaboration | ||
March 2019 | ||
Abstract: A search for the standard model production of four top quarks ($\mathrm{pp \rightarrow t\bar{t}t\bar{t}}$) is reported using events with single-lepton ($\mathrm{e}$, $\mu$) + jets and opposite-sign dilepton ($\mu^+\mu^-$, $\mu^\pm \mathrm{e}^\mp$, or $\mathrm{e^+e^-}$) + jets signatures. The events are collected in proton-proton collisions recorded by the CMS detector at the LHC at $\sqrt{s}= $ 13 TeV in a sample corresponding to an integrated luminosity of 35.8 fb$^{-1}$. A multivariate analysis using global event and jet properties based on boosted decision trees is used to discriminate $\mathrm{t\bar{t}t\bar{t}}$ 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 $\mathrm{t\bar{t}t\bar{t}}$ production in the standard model of 48 fb at 95$%$ confidence level. When combined with the previous measurement of $\sigma_\mathrm{t\bar{t}t\bar{t}}$ 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 $\sigma_\mathrm{t\bar{t}t\bar{t}} = $ 13$^{+11}_{-9}$ fb. | ||
Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 11 (2019) 082. The superseded preliminary plots can be found here. |
Figures | |
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Figure 1:
Representative diagrams for $\mathrm{t\bar{t}t\bar{t}}$ production at the lowest order in the SM. |
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Figure 2:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 2-a:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 2-b:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 3:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 3-a:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 3-b:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 3-c:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 3-d:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 4:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 4-a:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 4-b:
Control distributions 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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total systematic and statistical uncertainty on the simulations added in quadrature. |
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Figure 5:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {{{\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
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Figure 5-a:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {{{\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
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Figure 5-b:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {{{\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
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Figure 6:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
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Figure 6-a:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
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Figure 6-b:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
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Figure 7:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {{\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
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Figure 7-a:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {{\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
png pdf |
Figure 7-b:
Control distributions of ${N_{\text {j}}}$ and ${T_{\text {trijet1}}}$ in the combined OS dilepton $ {{\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 a relative difference with respect to MC prediction is also shown. The shaded band represents the total uncertainty on the main background |
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Figure 8:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single-muon channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} =$ 7, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3,$ \geq$ 4. Non-equidistant partitioning of the domain of the MVA discriminant was chosen to achieve approximately uniform distribution of the ${{\mathrm {t}\overline {\mathrm {t}}}}$ background. Dots represent data. Vertical error bars show the statistical uncertainties in the data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty on 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 on the background prediction. 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 ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single-muon (a) and single-electron (b) channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} =$ 8, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3,$\geq$ 4. Other details as in Fig. 8. |
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Figure 9-a:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single-muon (a) and single-electron (b) channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} =$ 8, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3,$\geq$ 4. Other details as in Fig. 8. |
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Figure 9-b:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single-muon (a) and single-electron (b) channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} =$ 8, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3,$\geq$ 4. Other details as in Fig. 8. |
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Figure 10:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single (a) muon, (b) electron channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} =$ 9, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq$ 4. Other details as in Fig. 8. |
png pdf |
Figure 10-a:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single (a) muon, (b) electron channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} =$ 9, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq$ 4. Other details as in Fig. 8. |
png pdf |
Figure 10-b:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single (a) muon, (b) electron channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} =$ 9, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq$ 4. Other details as in Fig. 8. |
png pdf |
Figure 11:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single (a) muon, (b) electron channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} \geq $ 10, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq$ 4. Other details as in Fig. 8. |
png pdf |
Figure 11-a:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single (a) muon, (b) electron channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} \geq $ 10, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq$ 4. Other details as in Fig. 8. |
png pdf |
Figure 11-b:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ distribution in the single (a) muon, (b) electron channel for events satisfying baseline single-lepton selection and $ {N_{\text {j}}} \geq $ 10, ${N_{\text {tags}}^{\text {m}}} =$ 2, 3, $\geq$ 4. Other details as in Fig. 8. |
png pdf |
Figure 12:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {dil}}}$ distributions in the $ {{{\mu ^+}} {{\mu ^-}}} $ channel for events satisfying baseline opposite-sign dilepton selection. Dots represent data. Vertical error bars show the statistical uncertainties in the data. The post-fit background predictions are shown as shaded histograms. Open boxes demonstrate the size of the pre-fit uncertainty on 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 on the background prediction. 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. |
png pdf |
Figure 13:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {dil}}}$ distributions in the (a) $ {{\mathrm {e}^+} {\mathrm {e}^-}} $, (b) $ {\mu} ^\pm {\mathrm {e}}^\mp $ channel for events satisfying baseline opposite-sign dilepton selection. Other details as in Fig. 12. |
png pdf |
Figure 13-a:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {dil}}}$ distributions in the (a) $ {{\mathrm {e}^+} {\mathrm {e}^-}} $, (b) $ {\mu} ^\pm {\mathrm {e}}^\mp $ channel for events satisfying baseline opposite-sign dilepton selection. Other details as in Fig. 12. |
png pdf |
Figure 13-b:
Post-fit ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {dil}}}$ distributions in the (a) $ {{\mathrm {e}^+} {\mathrm {e}^-}} $, (b) $ {\mu} ^\pm {\mathrm {e}}^\mp $ channel for events satisfying baseline opposite-sign dilepton selection. Other details as in Fig. 12. |
Tables | |
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Table 1:
Uncertainties that affect the normalization of the data sets and shapes of the ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {lj}}}$ and ${D_{\mathrm{t\bar{t}t\bar{t}}}^{\text {dil}}}$ discriminants |
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Table 2:
Maximum-likelihood signal-strength and cross section estimates, as well as the expected and observed significance of SM $\mathrm{t\bar{t}t\bar{t}}$ production. The results for the two analyses from this note are shown separately and combined. The values quoted for the uncertainties on the signal-strengths and cross sections are the one standard deviation values and include all statistical and systematic uncertainties. |
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Table 3:
Expected and observed 95% CL upper limits on SM $\mathrm{t\bar{t}t\bar{t}}$ production as a multiple of ${\sigma _{\mathrm{t\bar{t}t\bar{t}}}^{\text {SM}}}$ and in fb. The results for the two analyses from this note are shown separately and combined. The values quoted for the uncertainties on the expected limits are the one standard deviation values and include all statistical and systematic uncertainties. |
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Table 4:
Linear parametrization coefficients, $\sigma _{k}^{\left (1\right)}$, of Eq. 6. The coefficients $\sigma _{k}^{\left (1\right)}$ are in units (fb TeV$ ^{2}$). |
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Table 5:
Quadratic parametrization coefficients, $\sigma _{j,k}^{\left (2\right)}$, of Eq. 6. The coefficients $\sigma _{j,k}^{\left (2\right)}$ are in units (fb TeV$ ^{4}$). |
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Table 6:
Expected and observed 95% CL intervals for selected coupling parameters. The intervals are extracted from upper limit on the $\mathrm{t\bar{t}t\bar{t}}$ production cross section in the EFT model, where only one selected operator has a non-vanishing contribution. |
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Table 7:
Expected and observed 95% CL intervals for selected coupling parameters when contribution of other operators is marginalized. |
Summary |
A search for the standard model (SM) $\mathrm{t\bar{t}t\bar{t}}$ production has been performed in final states with one or two oppositely charged electrons or muons. The observed yields attributed to $\mathrm{t\bar{t}t\bar{t}}$ production are consistent with the SM predictions and a measured value for the $\mathrm{t\bar{t}t\bar{t}}$ cross section of 0$^{\,+\,{20}}$ fb has been obtained with an observed significance of 0.0 standard deviations. Combining this result with a previous same-sign dilepton and multilepton search [25] the resulting cross section is 13$^{+{11}}_{-{9}}$ fb with an observed significance of 1.4 standard deviations. The data were analysed in the effective field theory framework. The limits on dimension-6 four-fermion operators coupling to third generation quarks were obtained. These results constitute one of the most stringent constraints on the four top quarks production to date and can be used for phenomenological reinterpretation of a wide range of new physics models. |
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