CMS-PAS-TOP-17-013 | ||

Measurement of jet substructure observables in $\mathrm{t \bar t}$ events from pp collisions at $\sqrt{s}= $ 13 TeV | ||

CMS Collaboration | ||

March 2018 | ||

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Abstract:
A measurement of differential jet substructure observables is presented using $\mathrm{t \bar t}$ lepton+jets events from proton-proton collisions at $\sqrt{s}= $ 13 TeV recorded by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Multiple jet substructure variables, such as the particle multiplicity, width, eccentricity, $p_\mathrm{T}$ dispersion, N-subjettiness ratios, generalized angularities, and energy correlation functions, are measured for inclusive jets, as well as for identified bottom, light-quark, and gluon jets from the $\mathrm{t \bar t}$ final state. The results are unfolded to the stable-particle level and compared to predictions from POWHEG interfaced with PYTHIA 8 and HERWIG 7.1, as well as from SHERPA 2 and DIRE. A reasonable agreement between the data and the Monte Carlo predictions is found. From a comparison of the jet width distribution to the prediction, it is shown that a lower value of the effective strong coupling in the PYTHIA 8 final-state parton shower is preferred.
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRD 98 (2018) 092014.The superseded preliminary plots can be found here. |

Figures | |

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Figure 1:
Transverse momentum distribution at the particle level, for inclusive jets (upper left), bottom jets (upper right), light-quark enriched jets (lower left), and gluon-enriched jets (lower right). The bottom panels show the corresponding ratios of the different MC predictions over POWHEG+PYTHIA 8. |

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Figure 1-a:
Transverse momentum distribution at the particle level, for inclusive jets (upper left), bottom jets (upper right), light-quark enriched jets (lower left), and gluon-enriched jets (lower right). The bottom panels show the corresponding ratios of the different MC predictions over POWHEG+PYTHIA 8. |

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Figure 1-b:
Transverse momentum distribution at the particle level, for inclusive jets (upper left), bottom jets (upper right), light-quark enriched jets (lower left), and gluon-enriched jets (lower right). The bottom panels show the corresponding ratios of the different MC predictions over POWHEG+PYTHIA 8. |

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Figure 1-c:
Transverse momentum distribution at the particle level, for inclusive jets (upper left), bottom jets (upper right), light-quark enriched jets (lower left), and gluon-enriched jets (lower right). The bottom panels show the corresponding ratios of the different MC predictions over POWHEG+PYTHIA 8. |

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Figure 1-d:
Transverse momentum distribution at the particle level, for inclusive jets (upper left), bottom jets (upper right), light-quark enriched jets (lower left), and gluon-enriched jets (lower right). The bottom panels show the corresponding ratios of the different MC predictions over POWHEG+PYTHIA 8. |

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Figure 2:
Charged particle multiplicity at the reconstructed level (left) and normalized and unfolded to the particle level (right), in inclusive jets measured in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. The reconstruction-level plot shows the sum of the expected contributions from each process (stacked histograms) compared to the data points (upper panel), and the ratio of the MC prediction (POWHEG+PYTHIA 8) to the data (lower panel), where the dashed band represents the uncertainty on the prediction affecting either the shape or both the shape and normalization of the distribution. The particle-level plot shows the normalized differential cross section (upper panel), and the ratio of multiple MC predictions to data (lower panel) where the grey band indicates the total uncertainty and the hatched black area the statistical uncertainty. |

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Figure 2-a:
Charged particle multiplicity at the reconstructed level (left) and normalized and unfolded to the particle level (right), in inclusive jets measured in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. The reconstruction-level plot shows the sum of the expected contributions from each process (stacked histograms) compared to the data points (upper panel), and the ratio of the MC prediction (POWHEG+PYTHIA 8) to the data (lower panel), where the dashed band represents the uncertainty on the prediction affecting either the shape or both the shape and normalization of the distribution. The particle-level plot shows the normalized differential cross section (upper panel), and the ratio of multiple MC predictions to data (lower panel) where the grey band indicates the total uncertainty and the hatched black area the statistical uncertainty. |

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Figure 2-b:
Charged particle multiplicity at the reconstructed level (left) and normalized and unfolded to the particle level (right), in inclusive jets measured in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. The reconstruction-level plot shows the sum of the expected contributions from each process (stacked histograms) compared to the data points (upper panel), and the ratio of the MC prediction (POWHEG+PYTHIA 8) to the data (lower panel), where the dashed band represents the uncertainty on the prediction affecting either the shape or both the shape and normalization of the distribution. The particle-level plot shows the normalized differential cross section (upper panel), and the ratio of multiple MC predictions to data (lower panel) where the grey band indicates the total uncertainty and the hatched black area the statistical uncertainty. |

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Figure 3:
Distributions of the scaled $ {p_{\mathrm {T}}} $ dispersion ($\lambda _0^{2*}$, left) and Les Houches angularity ($\lambda _{0.5}^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 3-a:
Distributions of the scaled $ {p_{\mathrm {T}}} $ dispersion ($\lambda _0^{2*}$, left) and Les Houches angularity ($\lambda _{0.5}^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 3-b:
Distributions of the scaled $ {p_{\mathrm {T}}} $ dispersion ($\lambda _0^{2*}$, left) and Les Houches angularity ($\lambda _{0.5}^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 4:
Distributions of the jet width ($\lambda _1^1$, left) and thrust ($\lambda _2^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 4-a:
Distributions of the jet width ($\lambda _1^1$, left) and thrust ($\lambda _2^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 4-b:
Distributions of the jet width ($\lambda _1^1$, left) and thrust ($\lambda _2^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 5:
Distributions of the Les Houches angularity ($\lambda _{0.5}^1$, left) and jet width ($\lambda _1^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 5-a:
Distributions of the Les Houches angularity ($\lambda _{0.5}^1$, left) and jet width ($\lambda _1^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 5-b:
Distributions of the Les Houches angularity ($\lambda _{0.5}^1$, left) and jet width ($\lambda _1^1$, right), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 6:
Distributions of the eccentricity $\varepsilon $ (left) and the N-subjettiness ratio $\tau _{21}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 6-a:
Distributions of the eccentricity $\varepsilon $ (left) and the N-subjettiness ratio $\tau _{21}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 6-b:
Distributions of the eccentricity $\varepsilon $ (left) and the N-subjettiness ratio $\tau _{21}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 7:
Distributions of N-subjettiness ratios $\tau _{32}$ (left) and $\tau _{43}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 7-a:
Distributions of N-subjettiness ratios $\tau _{32}$ (left) and $\tau _{43}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 7-b:
Distributions of N-subjettiness ratios $\tau _{32}$ (left) and $\tau _{43}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 8:
Distributions of the groomed momentum fraction $z_g$ (left) and the angle between the groomed subjets $\Delta R_g$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 8-a:
Distributions of the groomed momentum fraction $z_g$ (left) and the angle between the groomed subjets $\Delta R_g$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 8-b:
Distributions of the groomed momentum fraction $z_g$ (left) and the angle between the groomed subjets $\Delta R_g$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 9:
Distribution of the soft drop multiplicity $n_{SD}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 10:
Distributions of energy correlation ratios $C_{1}^{ (0.0)}$ (left) and $C_{1}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 10-a:
Distributions of energy correlation ratios $C_{1}^{ (0.0)}$ (left) and $C_{1}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 10-b:
Distributions of energy correlation ratios $C_{1}^{ (0.0)}$ (left) and $C_{1}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 11:
Distributions of energy correlation ratios $C_{1}^{ (0.0)}$ (left) and $C_{1}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 11-a:
Distributions of energy correlation ratios $C_{1}^{ (0.0)}$ (left) and $C_{1}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 11-b:
Distributions of energy correlation ratios $C_{1}^{ (0.0)}$ (left) and $C_{1}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 12:
Distributions of energy correlation ratios $C_{2}^{ (0.0)}$ (left) and $C_{2}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 12-a:
Distributions of energy correlation ratios $C_{2}^{ (0.0)}$ (left) and $C_{2}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 12-b:
Distributions of energy correlation ratios $C_{2}^{ (0.0)}$ (left) and $C_{2}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 13:
Distributions of energy correlation ratios $C_{3}^{ (0.0)}$ (left) and $C_{3}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 13-a:
Distributions of energy correlation ratios $C_{3}^{ (0.0)}$ (left) and $C_{3}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 13-b:
Distributions of energy correlation ratios $C_{3}^{ (0.0)}$ (left) and $C_{3}^{ (1.0)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 14:
Distributions of the energy correlation ratios $M_{2}^{ (1)}$ (left) and $N_{2}^{ (1)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 14-a:
Distributions of the energy correlation ratios $M_{2}^{ (1)}$ (left) and $N_{2}^{ (1)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 14-b:
Distributions of the energy correlation ratios $M_{2}^{ (1)}$ (left) and $N_{2}^{ (1)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 15:
Distribution of the energy correlation ratio $N_{3}^{ (1)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. Data (points) are compared to different MC predictions absolutely (upper), and as MC/data ratios (lower). |

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Figure 16:
Distributions of the charged multiplicity (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion ($\lambda _0^{2*}$) (upper right), Les Houches angularity ($\lambda _{0.5}^1$) (lower left), and the energy correlation ratio $C_{3}^{ (1.0)}$ (lower right), unfolded to the particle level, for jets of different flavors measured in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. |

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Figure 16-a:
Distributions of the charged multiplicity (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion ($\lambda _0^{2*}$) (upper right), Les Houches angularity ($\lambda _{0.5}^1$) (lower left), and the energy correlation ratio $C_{3}^{ (1.0)}$ (lower right), unfolded to the particle level, for jets of different flavors measured in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. |

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Figure 16-b:
Distributions of the charged multiplicity (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion ($\lambda _0^{2*}$) (upper right), Les Houches angularity ($\lambda _{0.5}^1$) (lower left), and the energy correlation ratio $C_{3}^{ (1.0)}$ (lower right), unfolded to the particle level, for jets of different flavors measured in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. |

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Figure 16-c:
Distributions of the charged multiplicity (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion ($\lambda _0^{2*}$) (upper right), Les Houches angularity ($\lambda _{0.5}^1$) (lower left), and the energy correlation ratio $C_{3}^{ (1.0)}$ (lower right), unfolded to the particle level, for jets of different flavors measured in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. |

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Figure 16-d:
Distributions of the charged multiplicity (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion ($\lambda _0^{2*}$) (upper right), Les Houches angularity ($\lambda _{0.5}^1$) (lower left), and the energy correlation ratio $C_{3}^{ (1.0)}$ (lower right), unfolded to the particle level, for jets of different flavors measured in $ {{\mathrm {t}\overline {\mathrm {t}}}} $ events at $\sqrt {s} = $ 13 TeV. |

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Figure 17:
Correlations of the jet-shapes observables used in this analysis obtained at particle level based on the full matrix (left), and of four (FSR-sensitive) observables with low correlation (right). |

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Figure 17-a:
Correlations of the jet-shapes observables used in this analysis obtained at particle level based on the full matrix (left), and of four (FSR-sensitive) observables with low correlation (right). |

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Figure 17-b:
Correlations of the jet-shapes observables used in this analysis obtained at particle level based on the full matrix (left), and of four (FSR-sensitive) observables with low correlation (right). |

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Figure 18:
Fit of $ {\alpha _{s}^{\text {FSR}}(m_{{\mathrm {Z}}})} $ using the jet width $\lambda _1^1$ (left), and a scan adding three other observables ($\varepsilon $, $z_{g}$, and $\tau _{43}$) lightly correlated with it and with each other (right). |

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Figure 18-a:
Fit of $ {\alpha _{s}^{\text {FSR}}(m_{{\mathrm {Z}}})} $ using the jet width $\lambda _1^1$ (left), and a scan adding three other observables ($\varepsilon $, $z_{g}$, and $\tau _{43}$) lightly correlated with it and with each other (right). |

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Figure 18-b:
Fit of $ {\alpha _{s}^{\text {FSR}}(m_{{\mathrm {Z}}})} $ using the jet width $\lambda _1^1$ (left), and a scan adding three other observables ($\varepsilon $, $z_{g}$, and $\tau _{43}$) lightly correlated with it and with each other (right). |

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Figure 19:
Scans of $ {\alpha _{s}^{\text {FSR}}(m_{{\mathrm {Z}}})} $ using the $\lambda $ and $C_1$ families of jet substructure observables. |

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Figure 19-a:
Scans of $ {\alpha _{s}^{\text {FSR}}(m_{{\mathrm {Z}}})} $ using the $\lambda $ and $C_1$ families of jet substructure observables. |

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Figure 19-b:
Scans of $ {\alpha _{s}^{\text {FSR}}(m_{{\mathrm {Z}}})} $ using the $\lambda $ and $C_1$ families of jet substructure observables. |

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Figure 20:
Systematic uncertainties for the jet width $\lambda _{1}^1$ (upper left), eccentricity $\varepsilon $ (upper right), groomed momentum fraction $z_{g}$ (lower left), and N-subjettiness ratio $\tau _{43}$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 20-a:
Systematic uncertainties for the jet width $\lambda _{1}^1$ (upper left), eccentricity $\varepsilon $ (upper right), groomed momentum fraction $z_{g}$ (lower left), and N-subjettiness ratio $\tau _{43}$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 20-b:
Systematic uncertainties for the jet width $\lambda _{1}^1$ (upper left), eccentricity $\varepsilon $ (upper right), groomed momentum fraction $z_{g}$ (lower left), and N-subjettiness ratio $\tau _{43}$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 20-c:
Systematic uncertainties for the jet width $\lambda _{1}^1$ (upper left), eccentricity $\varepsilon $ (upper right), groomed momentum fraction $z_{g}$ (lower left), and N-subjettiness ratio $\tau _{43}$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 20-d:
Systematic uncertainties for the jet width $\lambda _{1}^1$ (upper left), eccentricity $\varepsilon $ (upper right), groomed momentum fraction $z_{g}$ (lower left), and N-subjettiness ratio $\tau _{43}$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 21:
Systematic uncertainties for charged multiplicity $\lambda _0^{0}$ (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion $\lambda _0^{2*}$ (upper right), Les Houches angularity $\lambda _{0.5}^1$ (lower left), and the jet thrust $\lambda _{1}^1$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 21-a:
Systematic uncertainties for charged multiplicity $\lambda _0^{0}$ (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion $\lambda _0^{2*}$ (upper right), Les Houches angularity $\lambda _{0.5}^1$ (lower left), and the jet thrust $\lambda _{1}^1$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 21-b:
Systematic uncertainties for charged multiplicity $\lambda _0^{0}$ (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion $\lambda _0^{2*}$ (upper right), Les Houches angularity $\lambda _{0.5}^1$ (lower left), and the jet thrust $\lambda _{1}^1$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 21-c:
Systematic uncertainties for charged multiplicity $\lambda _0^{0}$ (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion $\lambda _0^{2*}$ (upper right), Les Houches angularity $\lambda _{0.5}^1$ (lower left), and the jet thrust $\lambda _{1}^1$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

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Figure 21-d:
Systematic uncertainties for charged multiplicity $\lambda _0^{0}$ (upper left), scaled $ {p_{\mathrm {T}}} $ dispersion $\lambda _0^{2*}$ (upper right), Les Houches angularity $\lambda _{0.5}^1$ (lower left), and the jet thrust $\lambda _{1}^1$ (lower right), compared to the full effect of FSR variations on the particle-level distributions. |

Tables | |

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Table 1:
$\chi ^{2}$ values for the data-MC comparison of the distributions of the four lightly-correlated jet substructure observables, $\lambda _{1}^{1}$, $\varepsilon $, $z_{g}$, and $\tau _{43}$. |

Summary |

A measurement of jet substructure observables in $ \mathrm{t\bar{t}} $ events from pp collisions at 13 TeV is presented, including several variables relevant for quark-gluon discrimination and heavy boosted object identification. The investigated observables are probes for the perturbative and non-perturbative phases of jet evolution, and their unfolded distributions have been derived for inclusive jets, as well as for samples enriched in jets originating from bottom quarks, light quarks, or gluons. The correlations between all jet substructure variables have been studied. Eliminating observables with a high level of correlation, a set of four variables is identified and used for quantifying the level of data-simulation agreement. Data are compared to theoretical predictions either based on NLO matrix-element calculations (POWHEG) interfaced with different generators for the parton shower and hadronization (either PYTHIA 8 or HERWIG 7), or based on SHERPA 2 with NLO corrections, as well as on the DIRE shower. Using the default tunes none of the predictions yields a good overall agreement. Thus, some further tuning of the models is required. For the POWHEG+PYTHIA 8 prediction, a better accord is achieved by lowering the default value of its (effective) strong coupling for final-state radiation, as confirmed by a one-parameter tuning to the jet width $\lambda_{1}^{1}$ yielding a value ${\alpha_{s}^{\text{FSR}}(m_{\mathrm{Z}})} = $ 0.1227 $\pm$ 0.0013. Besides tuning and improving final-state parton showers, the present data can also be compared against modern QCD analytical calculations for infrared and/or collinear-safe observables that include higher fixed-order corrections as well as logarithmic resummations. |

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Compact Muon Solenoid LHC, CERN |