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CMS-PAS-TOP-16-006
A measurement of the inclusive ${\rm t\bar{t}}$ production cross section in proton-proton collisions at $\sqrt{s}=$ 13 TeV using events with one isolated charged lepton and at least one jet
Abstract: A measurement of the ${\rm t\bar{t}}$ production cross section at $\sqrt{s}=$ 13 TeV is presented using 2.3 fb$^{-1}$ of proton-proton collision data acquired by the CMS detector. Final states including one isolated charged lepton (electron or muon) and at least one jet are selected and categorized according to the multiplicity of jets. From a likelihood fit to the invariant mass of the isolated lepton and a jet identified as stemming from the fragmentation and hadronization of b quark, the cross section is measured to be $\sigma(\rm t\bar{t})=$ 834.6 $\pm$ 2.5 (stat) $\pm$ 22.8 (syst) $\pm$ 22.5 (lumi) pb in agreement with the standard model prediction. Using the expected dependency of the cross section on the top quark pole mass at NNLO+NNLL we determine the latter to be $m_{\rm t}=$ 172.3$^{+2.7}_{-2.3}$ GeV.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Event yields for data and expected signal and backgrounds for each of the 11 independent categories. Distributions are superimposed for all charges or lepton flavor. Each bin represents a required jet (j) and b-tag (t) multiplicity. The uncertainties are of statistical nature.

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Figure 2-a:
Pre-fit distributions for the observables used in the fit, combined for all leptons and charges. The a,b,d,f (c,e,g) figures represent the $M(\ell ,\mathrm{ b } )$ ($\text{min}M(\ell ,\mathrm{ b } )$) distributions used events with 1 (2) b-tagged jet(s). From a to f: events with 1, 2, 3 or at least 4 jets. The top panels show the ratio between data and expectations. The uncertainties represented are of statistical nature.

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Figure 2-b:
Pre-fit distributions for the observables used in the fit, combined for all leptons and charges. The a,b,d,f (c,e,g) figures represent the $M(\ell ,\mathrm{ b } )$ ($\text{min}M(\ell ,\mathrm{ b } )$) distributions used events with 1 (2) b-tagged jet(s). From a to f: events with 1, 2, 3 or at least 4 jets. The top panels show the ratio between data and expectations. The uncertainties represented are of statistical nature.

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Figure 2-c:
Pre-fit distributions for the observables used in the fit, combined for all leptons and charges. The a,b,d,f (c,e,g) figures represent the $M(\ell ,\mathrm{ b } )$ ($\text{min}M(\ell ,\mathrm{ b } )$) distributions used events with 1 (2) b-tagged jet(s). From a to f: events with 1, 2, 3 or at least 4 jets. The top panels show the ratio between data and expectations. The uncertainties represented are of statistical nature.

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Figure 2-d:
Pre-fit distributions for the observables used in the fit, combined for all leptons and charges. The a,b,d,f (c,e,g) figures represent the $M(\ell ,\mathrm{ b } )$ ($\text{min}M(\ell ,\mathrm{ b } )$) distributions used events with 1 (2) b-tagged jet(s). From a to f: events with 1, 2, 3 or at least 4 jets. The top panels show the ratio between data and expectations. The uncertainties represented are of statistical nature.

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Figure 2-e:
Pre-fit distributions for the observables used in the fit, combined for all leptons and charges. The a,b,d,f (c,e,g) figures represent the $M(\ell ,\mathrm{ b } )$ ($\text{min}M(\ell ,\mathrm{ b } )$) distributions used events with 1 (2) b-tagged jet(s). From a to f: events with 1, 2, 3 or at least 4 jets. The top panels show the ratio between data and expectations. The uncertainties represented are of statistical nature.

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Figure 2-f:
Pre-fit distributions for the observables used in the fit, combined for all leptons and charges. The a,b,d,f (c,e,g) figures represent the $M(\ell ,\mathrm{ b } )$ ($\text{min}M(\ell ,\mathrm{ b } )$) distributions used events with 1 (2) b-tagged jet(s). From a to f: events with 1, 2, 3 or at least 4 jets. The top panels show the ratio between data and expectations. The uncertainties represented are of statistical nature.

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Figure 2-g:
Pre-fit distributions for the observables used in the fit, combined for all leptons and charges. The a,b,d,f (c,e,g) figures represent the $M(\ell ,\mathrm{ b } )$ ($\text{min}M(\ell ,\mathrm{ b } )$) distributions used events with 1 (2) b-tagged jet(s). From a to f: events with 1, 2, 3 or at least 4 jets. The top panels show the ratio between data and expectations. The uncertainties represented are of statistical nature.

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Figure 3-a:
a: Variation of the PLR as function of the signal strength for the shapes-based analysis. For comparison the cross check cut-in-categories is also shown. b: Comparison of the values of the signal strength extracted for different combinations of events. The error bars represent the statistical uncertainty while the squares represent the total uncertainty of the fits.

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Figure 3-b:
a: Variation of the PLR as function of the signal strength for the shapes-based analysis. For comparison the cross check cut-in-categories is also shown. b: Comparison of the values of the signal strength extracted for different combinations of events. The error bars represent the statistical uncertainty while the squares represent the total uncertainty of the fits.

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Figure 4:
Variation of the PLR as function of the top quark pole mass. The scan of the PLR, using the a-priori set of nuisances and expectations (Asimov dataset), at $m_\mathrm{ t } =$ 172.5 GeV is shown for comparison.
Tables

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Table 1:
Estimated impact of each source of uncertainty in % on the cross-check and shape analyses.

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Table 2:
Estimated impact of each source of uncertainty in GeV on the measurement of $m_\mathrm{ t } $.
Summary
We have presented a measurement of the ${\rm t\bar{t}}$ production cross section at $\sqrt{s} =$ 13 TeV in final states containing one isolated lepton and at least one jet. The acceptance in the visible phase space is estimated with an uncertainty of 1.5% and to have a very mild dependency on the $m_\mathrm{t }$. By performing a simultaneous fit to event distributions in 44 independent categories we measure the strength of the $\mathrm{ t \bar{t} }$ signal with respect to the NLO+NNLL [43] computation with an uncertainty of 3.9%. We measure an inclusive $\mathrm{ t \bar{t} }$ production cross section which is compatible with SM predictions: $\sigma(\mathrm{ t \bar{t} })=$ 834.6 $\pm$ 2.5 (stat) $\pm$ 22.8 (syst) $\pm$ 22.5 (lumi) pb. In addition, the pole mass is extracted at NNLO, using the NNPDF 3.0 PDF set. A value of $m_\mathrm{t }=$ 172.3$^{+2.7}_{-2.3}$ GeV is obtained.
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Compact Muon Solenoid
LHC, CERN