CMS-PAS-TOP-16-007 | ||

Measurement of particle level differential $\mathrm{ t \bar{t} }$ cross sections in the dilepton channel at $\sqrt{s} =$ 13 TeV | ||

CMS Collaboration | ||

August 2016 | ||

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Abstract:
The normalised differential cross section for top quark pair production is measured in the dilepton ($\mathrm{e}^{+}\mathrm{e}^{-}$, $\mu^{+}\mu^{-}$, and $\mu^{\mp}\mathrm{e}^{\pm}$) decay channel in proton-proton collisions at a center-of-mass energy of 13 TeV. The measurements are performed with data corresponding to an integrated luminosity of 2.2 fb$^{-1}$ collected in 2015 using the CMS detector at the LHC. The cross section is measured differentially as a function of the kinematic properties of the leptons, b jets, top quarks, and top quark pairs at particle level. The results are compared to several models of perturbative QCD and found to be in agreement with the standard model predictions.
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Links:
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These preliminary results are superseded in this paper, JHEP 04 (2018) 060.The superseded preliminary plots can be found here. |

Figures | |

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Figure 1-a:
Reconstructed $p_{\mathrm{T}}^{\ell}$, $p_{\mathrm{T}}^{\mathrm{j}}$, $p_{\mathrm{T}}^{\mathrm{t}}$, and $y^{\mathrm{t}}$ distributions. All corrections described in the text are applied to the simulation. |

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Figure 1-b:
Reconstructed $p_{\mathrm{T}}^{\ell}$, $p_{\mathrm{T}}^{\mathrm{j}}$, $p_{\mathrm{T}}^{\mathrm{t}}$, and $y^{\mathrm{t}}$ distributions. All corrections described in the text are applied to the simulation. |

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Figure 1-c:
Reconstructed $p_{\mathrm{T}}^{\ell}$, $p_{\mathrm{T}}^{\mathrm{j}}$, $p_{\mathrm{T}}^{\mathrm{t}}$, and $y^{\mathrm{t}}$ distributions. All corrections described in the text are applied to the simulation. |

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Figure 1-d:
Reconstructed $p_{\mathrm{T}}^{\ell}$, $p_{\mathrm{T}}^{\mathrm{j}}$, $p_{\mathrm{T}}^{\mathrm{t}}$, and $y^{\mathrm{t}}$ distributions. All corrections described in the text are applied to the simulation. |

png pdf |
Figure 2-a:
Reconstructed $p_{\mathrm{T}}^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $y^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $M^{ {\mathrm {t}\overline {\mathrm {t}}} }$, and $\Delta \phi ^{ {\mathrm {t}\overline {\mathrm {t}}} }$ distributions. All corrections described in the text are applied to the simulation. |

png pdf |
Figure 2-b:
Reconstructed $p_{\mathrm{T}}^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $y^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $M^{ {\mathrm {t}\overline {\mathrm {t}}} }$, and $\Delta \phi ^{ {\mathrm {t}\overline {\mathrm {t}}} }$ distributions. All corrections described in the text are applied to the simulation. |

png pdf |
Figure 2-c:
Reconstructed $p_{\mathrm{T}}^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $y^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $M^{ {\mathrm {t}\overline {\mathrm {t}}} }$, and $\Delta \phi ^{ {\mathrm {t}\overline {\mathrm {t}}} }$ distributions. All corrections described in the text are applied to the simulation. |

png pdf |
Figure 2-d:
Reconstructed $p_{\mathrm{T}}^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $y^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $M^{ {\mathrm {t}\overline {\mathrm {t}}} }$, and $\Delta \phi ^{ {\mathrm {t}\overline {\mathrm {t}}} }$ distributions. All corrections described in the text are applied to the simulation. |

png pdf |
Figure 3-a:
Normalised differential cross section as a function of lepton, jet, and top quark ${p_{\mathrm {T}}}$ and top quark rapidity, measured at particle level in the visible phase space and combining the distributions for top quarks and antiquarks. The error bars on the data points indicate the total (combined statistical and systematic) uncertainties, while the dark shaded band shows the statistical uncertainty. The measurements are compared to predictions from POWHEG+PHYTHIA-8, MG5-aMCatNLO+PYTHIA-8[FXFX], MG5-aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++ . |

png pdf |
Figure 3-b:
Normalised differential cross section as a function of lepton, jet, and top quark ${p_{\mathrm {T}}}$ and top quark rapidity, measured at particle level in the visible phase space and combining the distributions for top quarks and antiquarks. The error bars on the data points indicate the total (combined statistical and systematic) uncertainties, while the dark shaded band shows the statistical uncertainty. The measurements are compared to predictions from POWHEG+PHYTHIA-8, MG5-aMCatNLO+PYTHIA-8[FXFX], MG5-aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++ . |

png pdf |
Figure 3-c:
Normalised differential cross section as a function of lepton, jet, and top quark ${p_{\mathrm {T}}}$ and top quark rapidity, measured at particle level in the visible phase space and combining the distributions for top quarks and antiquarks. The error bars on the data points indicate the total (combined statistical and systematic) uncertainties, while the dark shaded band shows the statistical uncertainty. The measurements are compared to predictions from POWHEG+PHYTHIA-8, MG5-aMCatNLO+PYTHIA-8[FXFX], MG5-aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++ . |

png pdf |
Figure 3-d:
Normalised differential cross section as a function of lepton, jet, and top quark ${p_{\mathrm {T}}}$ and top quark rapidity, measured at particle level in the visible phase space and combining the distributions for top quarks and antiquarks. The error bars on the data points indicate the total (combined statistical and systematic) uncertainties, while the dark shaded band shows the statistical uncertainty. The measurements are compared to predictions from POWHEG+PHYTHIA-8, MG5-aMCatNLO+PYTHIA-8[FXFX], MG5-aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++ . |

png pdf |
Figure 4-a:
Normalised differential cross section as a function of $p_{\mathrm{T}}^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $y^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $M^{ {\mathrm {t}\overline {\mathrm {t}}} }$, and $\Delta \phi ^{ {\mathrm {t}\overline {\mathrm {t}}} }$ for the top quarks or antiquarks, measured at particle level in the visible phase space. The error bars on the data points indicate the total (combined statistical and systematic) uncertainties, while the dark shaded band shows the statistical uncertainty. The measurements are compared to predictions from POWHEG+PHYTHIA-8, MG5-aMCatNLO+PYTHIA-8[FXFX], MG5-aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++ . |

png pdf |
Figure 4-b:
Normalised differential cross section as a function of $p_{\mathrm{T}}^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $y^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $M^{ {\mathrm {t}\overline {\mathrm {t}}} }$, and $\Delta \phi ^{ {\mathrm {t}\overline {\mathrm {t}}} }$ for the top quarks or antiquarks, measured at particle level in the visible phase space. The error bars on the data points indicate the total (combined statistical and systematic) uncertainties, while the dark shaded band shows the statistical uncertainty. The measurements are compared to predictions from POWHEG+PHYTHIA-8, MG5-aMCatNLO+PYTHIA-8[FXFX], MG5-aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++ . |

png pdf |
Figure 4-c:
Normalised differential cross section as a function of $p_{\mathrm{T}}^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $y^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $M^{ {\mathrm {t}\overline {\mathrm {t}}} }$, and $\Delta \phi ^{ {\mathrm {t}\overline {\mathrm {t}}} }$ for the top quarks or antiquarks, measured at particle level in the visible phase space. The error bars on the data points indicate the total (combined statistical and systematic) uncertainties, while the dark shaded band shows the statistical uncertainty. The measurements are compared to predictions from POWHEG+PHYTHIA-8, MG5-aMCatNLO+PYTHIA-8[FXFX], MG5-aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++ . |

png pdf |
Figure 4-d:
Normalised differential cross section as a function of $p_{\mathrm{T}}^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $y^{ {\mathrm {t}\overline {\mathrm {t}}} }$, $M^{ {\mathrm {t}\overline {\mathrm {t}}} }$, and $\Delta \phi ^{ {\mathrm {t}\overline {\mathrm {t}}} }$ for the top quarks or antiquarks, measured at particle level in the visible phase space. The error bars on the data points indicate the total (combined statistical and systematic) uncertainties, while the dark shaded band shows the statistical uncertainty. The measurements are compared to predictions from POWHEG+PHYTHIA-8, MG5-aMCatNLO+PYTHIA-8[FXFX], MG5-aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++ . |

Tables | |

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Table 1:
Summary of object definitions at the particle level. |

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Table 2:
Median systematic uncertainties in the normalised differential cross section for three representative kinematic variables. The maximum over all measured variables is given in the last column. |

Summary |

The normalised differential cross section for top quark pair production is measured in the dilepton decay channel in pp collisions at $\sqrt{s} =$ 13 TeV with data corresponding to an integrated luminosity of 2.2 fb$^{-1}$. The differential cross section is measured as a function of $p_{\mathrm{T}}^{\ell}$, $p_{\mathrm{T}}^{\mathrm{j}}$, $p_{\mathrm{T}}^{\mathrm{t}}$, $y^{\mathrm{t}}$, $p_{\mathrm{T}}^{\mathrm{ t \bar{t} }}$, $y^{\mathrm{ t \bar{t} }}$, $M^{\mathrm{ t \bar{t} }}$, and $\Delta \phi^{\mathrm{ t \bar{t} }}$ at particle level in the visible phase space. The measurements are compared to the predictions from POWHEG+PHYTHIA-8, aMCatNLO+PYTHIA-8[FXFX], aMCatNLO+PYTHIA-8[MLM], and POWHEG+HERWIG++, and are found to be in agreement with the standard model. |

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Compact Muon Solenoid LHC, CERN |