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| CMS-PAS-TOP-17-009 | ||
| Search for the standard model production of four top quarks with same-sign and multilepton final states in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| September 2017 | ||
| Abstract: The standard model production of four top quarks ($\mathrm{t\overline{t}t\overline{t}}$) is studied by the CMS Collaboration using events containing at least three leptons (e, $\mu$) or a same-sign pair. The events are produced in proton-proton collisions with a center-of-mass energy of 13 TeV at the LHC, and the data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$, recorded in 2016. Jet multiplicity and flavor are used to enhance signal sensitivity, and dedicated control regions are used to constrain the dominant standard model backgrounds. The observed (expected) significance is 1.6 (1.0) standard deviations, and the $\mathrm{t\overline{t}t\overline{t}}$ cross section is measured to be 16.9$^{+13.8}_{-11.4}$ fb, in agreement with next-to-leading-order standard model predictions. These results are also used to constrain the Yukawa coupling of the top quark. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, EPJC 78 (2018) 140. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Representative Feynman diagrams for ${{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}}$ production at LO in the SM. |
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Figure 1-a:
A representative Feynman diagram for ${{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}}$ production at LO in the SM. |
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Figure 1-b:
A representative Feynman diagram for ${{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}}$ production at LO in the SM. |
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Figure 1-c:
A representative Feynman diagram for ${{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}}$ production at LO in the SM. |
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Figure 2:
Distributions of the main analysis variables in the signal regions (SRs 1-8), before the fit to data: $ {N_\text {jets}} $, $ {N_\text {b}} $, $ {H_{\mathrm {T}}} $, and $ {p_{\mathrm {T}}^{\text {miss}}} $, where the last bin includes the overflow. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panels show the ratio of the observed event yield and the total background prediction. |
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Figure 2-a:
Distribution of $ {N_\text {jets}} $ in the signal regions (SRs 1-8), before the fit to data, where the last bin includes the overflow. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panel shows the ratio of the observed event yield and the total background prediction. |
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Figure 2-b:
Distribution of $ {N_\text {b}} $ in the signal regions (SRs 1-8), before the fit to data, where the last bin includes the overflow. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panel shows the ratio of the observed event yield and the total background prediction. |
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Figure 2-c:
Distribution of $ {H_{\mathrm {T}}} $ in the signal regions (SRs 1-8), before the fit to data, where the last bin includes the overflow. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panel shows the ratio of the observed event yield and the total background prediction. |
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Figure 2-d:
Distribution of $ {p_{\mathrm {T}}^{\text {miss}}} $ in the signal regions (SRs 1-8), before the fit to data, where the last bin includes the overflow. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panel shows the ratio of the observed event yield and the total background prediction. |
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Figure 3:
The $ {N_\text {jets}} $ (left) and $ {N_\text {b}} $ (right) distributions in the ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{W}}$ (top) and ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z}}$ (bottom) control regions, before the fit to data. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panels show the ratio of the observed event yield and the total background prediction. |
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Figure 3-a:
The $ {N_\text {jets}} $ distribution in the ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{W}}$ control region, before the fit to data. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panels show the ratio of the observed event yield and the total background prediction. |
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Figure 3-b:
The $ {N_\text {b}} $ distribution in the ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{W}}$ control region, before the fit to data. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panels show the ratio of the observed event yield and the total background prediction. |
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Figure 3-c:
The $ {N_\text {jets}} $ distribution in the ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z}}$ control region, before the fit to data. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panels show the ratio of the observed event yield and the total background prediction. |
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Figure 3-d:
The $ {N_\text {b}} $ distribution in the ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z}}$ control region, before the fit to data. The hatched area represents the total uncertainty in the SM background prediction, while the solid line represents the $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ signal, scaled by a factor of 5, assuming the SM cross section calculation from Ref. [17]. The upper panels show the ratio of the observed event yield and the total background prediction. |
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Figure 4:
Observed yields in the analysis control and signal regions (left, in log scale), and signal regions only (right, in linear scale), compared to the post-fit predictions for signal and background processes. The hatched area represents the total uncertainty in the signal and background predictions. The upper panels show the ratio of the observed event yield and the total prediction of signal and background. |
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Figure 4-a:
Observed yields in the analysis control and signal regions (in log scale)compared to the post-fit predictions for signal and background processes. The hatched area represents the total uncertainty in the signal and background predictions. The upper panel shows the ratio of the observed event yield and the total prediction of signal and background. |
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Figure 4-b:
Observed yields in the signal regions (in linear scale), compared to the post-fit predictions for signal and background processes. The hatched area represents the total uncertainty in the signal and background predictions. The upper panel shows the ratio of the observed event yield and the total prediction of signal and background. |
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Figure 5:
The expected $ {{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}} $ cross section, $\sigma ({{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}})$, as a function of $|y_{\rm {t}}/y_{\rm {t}}^{\rm {SM}}|$, the absolute value of the ratio of the top quark Yukawa coupling and its SM value (curved band), compared with the measured $\sigma ({{\mathrm{t} {}\mathrm{\bar{t}}} {\mathrm{t} {}\mathrm{\bar{t}}}})$ (horizontal band), and its 95% CL upper limit (horizontal line). See text for details. |
| Tables | |
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Table 1:
Kinematic requirements for leptons and jets. |
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Table 2:
Definitions of the eight SRs and the two control regions for ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{W}}$ (CRW) and ${{\mathrm{t} {}\mathrm{\bar{t}}} \mathrm{Z}}$ (CRZ). |
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Table 3:
Summary of the sources of uncertainty and their effect on the yields of different processes in the SRs. The first two groups list experimental and theoretical uncertainties, respectively, assigned to processes estimated using simulation. The third group lists uncertainties assigned to processes whose yield is estimated from data. |
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Table 4:
The post-fit predicted background, signal, and total yields with their uncertainties and the observed number of events in the control and signal regions. |
| Summary |
| We have presented the results of a search for the standard model ${\mathrm{t\bar{t}}\mathrm{t\bar{t}}} $ process at the LHC, using data from $\sqrt{s} = $ 13 TeV proton-proton collisions corresponding to an integrated luminosity of 35.9 fb$^{-1}$, collected with the CMS detector in 2016. The analysis strategy uses same-sign dilepton as well as three (or more) lepton events, relying on jet multiplicity and jet flavor to define search regions that are used to probe the ${\mathrm{t\bar{t}}\mathrm{t\bar{t}}} $ process. Combining these regions yields a significance of 1.6 standard deviations with respect to the background-only hypothesis, and a measured ${\mathrm{t\bar{t}}\mathrm{t\bar{t}}} $ cross section of 16.9$^{+13.8}_{-11.4} $ fb, in agreement with the standard model predictions. The results are also interpreted to constrain the ratio of the top quark Yukawa coupling to its SM value, $|y_{\rm{t}}/y_{\rm{t}}^{\rm{SM}}| < $ 2.27 at 95% confidence level. |
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