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| CMS-TOP-17-013 ; CERN-EP-2018-214 | ||
| Measurement of jet substructure observables in $\mathrm{t\bar{t}}$ events from proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 22 August 2018 | ||
| Phys. Rev. D 98 (2018) 092014 | ||
| Abstract: A measurement of jet substructure observables is presented using $\mathrm{t\bar{t}}$ events in the lepton+jets channel from proton-proton collisions at $\sqrt{s} = $ 13 TeV recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Multiple jet substructure observables are measured for jets identified as bottom, light-quark, and gluon jets, as well as for inclusive jets (no flavor information). The results are unfolded to the particle level and compared to next-to-leading-order predictions from POWHEG interfaced with the parton shower generators PYTHIA 8 and HERWIG 7, as well as from SHERPA 2 and DIRE 2. A value of the strong coupling at the Z boson mass, ${\alpha_{S}(m_{\mathrm{Z}})} =$ 0.115$^{+0.015}_{-0.013}$, is extracted from the substructure data at leading-order plus leading-log accuracy. | ||
| Links: e-print arXiv:1808.07340 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Multiplicity of b-tagged jets in events with exactly one isolated lepton and four jets (left), and multiplicity of untagged jets yielding a W boson candidate with $ {| m_{jj}-80.4 |} < $ 15 GeV after requiring two b-tagged jets (right). These reconstruction-level plots show the sum of the expected contributions from each process (stacked histograms) compared to the data points (upper panels), and the ratio of the MC prediction (POWHEG+PYTHIA-8) to the data (lower panels) where the black shaded band represents the statistical uncertainty on the data. The systematic uncertainties on the MC prediction are represented by hatched areas, taking into account either the total uncertainty or shape variations only. |
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Figure 1-a:
Multiplicity of b-tagged jets in events with exactly one isolated lepton and four jets. This reconstruction-level plot shows the sum of the expected contributions from each process (stacked histograms) compared to the data points (upper panels), and the ratio of the MC prediction (POWHEG+PYTHIA-8) to the data (lower panel) where the black shaded band represents the statistical uncertainty on the data. The systematic uncertainties on the MC prediction are represented by hatched areas, taking into account either the total uncertainty or shape variations only. |
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Figure 1-b:
Multiplicity of untagged jets yielding a W boson candidate with $ {| m_{jj}-80.4 |} < $ 15 GeV after requiring two b-tagged jets. This reconstruction-level plot shows the sum of the expected contributions from each process (stacked histograms) compared to the data points (upper panels), and the ratio of the MC prediction (POWHEG+PYTHIA-8) to the data (lower panel) where the black shaded band represents the statistical uncertainty on the data. The systematic uncertainties on the MC prediction are represented by hatched areas, taking into account either the total uncertainty or shape variations only. |
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Figure 2:
Transverse momentum distribution at the particle level for inclusive jets (upper left), bottom-quark jets (upper right), light-quark-enriched jets (lower left), and gluon-enriched jets (lower right). The sub-panels show the corresponding ratios of the different MC predictions over POWHEG+PYTHIA-8 (PP8). |
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Figure 2-a:
Transverse momentum distribution at the particle level for inclusive jets. The sub-panel shows the corresponding ratios of the different MC predictions over POWHEG+PYTHIA-8 (PP8). |
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Figure 2-b:
Transverse momentum distribution at the particle level for bottom-quark jets. The sub-panel shows the corresponding ratios of the different MC predictions over POWHEG+PYTHIA-8 (PP8). |
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Figure 2-c:
Transverse momentum distribution at the particle level for light-quark-enriched jets. The sub-panel shows the corresponding ratios of the different MC predictions over POWHEG+PYTHIA-8 (PP8). |
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Figure 2-d:
Transverse momentum distribution at the particle level for gluon-enriched jets. The sub-panel shows the corresponding ratios of the different MC predictions over POWHEG+PYTHIA-8 (PP8). |
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Figure 3:
Systematic uncertainties for the charged multiplicity $\lambda _{0}^{0}$ ($N$) (upper left), jet eccentricity $\varepsilon $ (upper right), groomed momentum fraction $z_\mathrm {g}$ (lower left), and angle between the groomed subjets $\Delta R_\mathrm {g}$ (lower right). The uncertainties from FSR and HERWIG (open markers) are compared to the full effect of these variations at the particle level (open markers with lines). |
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Figure 3-a:
Systematic uncertainties for the charged multiplicity $\lambda _{0}^{0}$ ($N$). The uncertainties from FSR and HERWIG (open markers) are compared to the full effect of these variations at the particle level (open markers with lines). |
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Figure 3-b:
Systematic uncertainties for the jet eccentricity $\varepsilon $. The uncertainties from FSR and HERWIG (open markers) are compared to the full effect of these variations at the particle level (open markers with lines). |
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Figure 3-c:
Systematic uncertainties for the groomed momentum fraction $z_\mathrm {g}$. The uncertainties from FSR and HERWIG (open markers) are compared to the full effect of these variations at the particle level (open markers with lines). |
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Figure 3-d:
Systematic uncertainties for the angle between the groomed subjets $\Delta R_\mathrm {g}$. The uncertainties from FSR and HERWIG (open markers) are compared to the full effect of these variations at the particle level (open markers with lines). |
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Figure 4:
Charged particle multiplicity $\lambda _{0}^{0}$ ($N$) at the reconstructed level after full event selection. The lower panel shows the ratio of the MC prediction (POWHEG+PYTHIA-8) to the data (lower panels) where the black shaded band represents the statistical uncertainty on the data. The systematic uncertainties on the MC prediction are represented by hatched areas, taking into account either the total uncertainty or shape variations only. |
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Figure 5:
Charged particle multiplicity $\lambda _{0}^{0}$ ($N$) normalized and unfolded to the particle level, for inclusive jets. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 6:
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. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 6-a:
Distribution of the scaled ${p_{\mathrm {T}}}$ dispersion ($\lambda _0^{2*}$), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 6-b:
Distribution of Les Houches angularity ($\lambda _{0.5}^1$), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 7:
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. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 7-a:
Distribution of the jet width ($\lambda _1^1$), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 7-b:
Distribution of the thrust ($\lambda _2^1$), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 8:
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+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 8-a:
Distribution of the jet width ($\lambda _1^1$), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 8-b:
Distribution of the thrust ($\lambda _2^1$), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 9:
Distribution of the eccentricity $\varepsilon $, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 10:
Distributions of the groomed momentum fraction $z_\mathrm {g}$ (left) and the soft-drop multiplicity $n_\mathrm {SD}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 10-a:
Distribution of the groomed momentum fraction $z_\mathrm {g}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 10-b:
Distribution of the soft-drop multiplicity $n_\mathrm {SD}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 11:
Distributions of the angle between the groomed subjets $\Delta R_\mathrm {g}$, unfolded to the particle level, for inclusive jets reconstructed with charged (left) and charged+neutral particles (right). Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 11-a:
Distribution of the angle between the groomed subjets $\Delta R_\mathrm {g}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 11-b:
Distribution of the angle between the groomed subjets $\Delta R_\mathrm {g}$, unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 12:
Distributions of the $\mathcal {N}$-subjettiness ratios $\tau _{21}$ (left) and $\tau _{32}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 12-a:
Distribution of the $\mathcal {N}$-subjettiness ratio $\tau _{21}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 12-b:
Distribution of the $\mathcal {N}$-subjettiness ratio $\tau _{32}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 13:
Distributions of the $\mathcal {N}$-subjettiness ratio $\tau _{43}$, unfolded to the particle level, for inclusive jets reconstructed with charged (left) and charged+neutral particles (right). Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 13-a:
Distribution of the $\mathcal {N}$-subjettiness ratio $\tau _{43}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 13-b:
Distribution of the $\mathcal {N}$-subjettiness ratio $\tau _{43}$, unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 14:
Distributions of energy correlation ratios $C_{1}^{\left (0\right)}$ (upper left), $C_{1}^{\left (1\right)}$ (upper right), $C_{2}^{\left (0\right)}$ (lower left) and $C_{2}^{\left (1\right)}$ (lower right), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 14-a:
Distribution of energy correlation ratio $C_{1}^{\left (0\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 14-b:
Distribution of energy correlation ratio $C_{1}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 14-c:
Distribution of energy correlation ratio $C_{2}^{\left (0\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 14-d:
Distribution of energy correlation ratio $C_{2}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 15:
Distributions of energy correlation ratios $C_{1}^{\left (0\right)}$ (left) and $C_{1}^{\left (1\right)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 15-a:
Distribution of energy correlation ratio $C_{1}^{\left (0\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 15-b:
Distribution of energy correlation ratio $C_{1}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 16:
Distributions of energy correlation ratios $C_{3}^{\left (0\right)}$ (left) and $C_{3}^{\left (1\right)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 16-a:
Distribution of the energy correlation ratio $C_{3}^{\left (0\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 16-b:
Distribution of the energy correlation ratio $C_{3}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 17:
Distributions of the energy correlation ratio $\mathrm {M}_{2}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged (left) or charged+neutral particles (right). Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 17-a:
Distribution of the energy correlation ratio $\mathrm {M}_{2}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 17-b:
Distribution of the energy correlation ratio $\mathrm {M}_{2}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged+neutral particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 18:
Distribution of the energy correlation ratios $\mathrm {N}_{2}^{\left (1\right)}$ (left) and $\mathrm {N}_{3}^{\left (1\right)}$ (right), unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 18-a:
Distribution of the energy correlation ratio $\mathrm {N}_{2}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 18-b:
Distribution of the energy correlation ratio $\mathrm {N}_{3}^{\left (1\right)}$, unfolded to the particle level, for inclusive jets reconstructed with charged particles. Data (points) are compared to different MC predictions (upper), and as MC/data ratios (lower). The hatched and shaded bands represent the statistical and total uncertainties, respectively. |
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Figure 19:
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 $C_{3}^{\left (1\right)}$ (lower right), unfolded to the particle level, for jets of different flavors. The second panel shows the corresponding ratios of the different flavors over the inclusive jets data. The sub-panels show the ratios of the different MC predictions over the bottom, light-quark-enriched, and gluon-enriched jet data. |
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Figure 19-a:
Distribution of the charged multiplicity, unfolded to the particle level, for jets of different flavors. The second panel shows the corresponding ratios of the different flavors over the inclusive jets data. The sub-panel shows the ratios of the different MC predictions over the bottom, light-quark-enriched, and gluon-enriched jet data. |
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Figure 19-b:
Distribution of the scaled ${p_{\mathrm {T}}}$ dispersion ($\lambda _0^{2*}$), unfolded to the particle level, for jets of different flavors. The second panel shows the corresponding ratios of the different flavors over the inclusive jets data. The sub-panel shows the ratios of the different MC predictions over the bottom, light-quark-enriched, and gluon-enriched jet data. |
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Figure 19-c:
Distribution of the Les Houches angularity ($\lambda _{0.5}^1$), unfolded to the particle level, for jets of different flavors. The second panel shows the corresponding ratios of the different flavors over the inclusive jets data. The sub-panel shows the ratios of the different MC predictions over the bottom, light-quark-enriched, and gluon-enriched jet data. |
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Figure 19-d:
Distribution of the energy correlation ratio $C_{3}^{\left (1\right)}$, unfolded to the particle level, for jets of different flavors. The second panel shows the corresponding ratios of the different flavors over the inclusive jets data. The sub-panel shows the ratios of the different MC predictions over the bottom, light-quark-enriched, and gluon-enriched jet data. |
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Figure 20:
Correlations of the jet-substructure observables used in this analysis obtained at the particle level. |
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Figure 21:
Correlations of the jet-substructure observables used in this analysis obtained at the particle level for the set of four minimally correlated observables. |
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Figure 22:
Scans of $\chi ^2$ as a function of ${\alpha _{S}^{\text {FSR}}(m_{{\mathrm {Z}}})}$, derived from the bottom-quark jet sample, for the minimally-correlated observables $\lambda _0^0$ ($N$), $\varepsilon $, $z_\mathrm {g}$, and $\Delta R_\mathrm {g}$ (left), and for $\Delta R_\mathrm {g}$ alone with uncertainties indicated by the shaded areas (right). |
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Figure 22-a:
Scan of $\chi ^2$ as a function of ${\alpha _{S}^{\text {FSR}}(m_{{\mathrm {Z}}})}$, derived from the bottom-quark jet sample, for the minimally-correlated observables $\lambda _0^0$ ($N$), $\varepsilon $, $z_\mathrm {g}$, and $\Delta R_\mathrm {g}$. |
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Figure 22-b:
Scan of $\chi ^2$ as a function of ${\alpha _{S}^{\text {FSR}}(m_{{\mathrm {Z}}})}$, derived from the bottom-quark jet sample, for $\Delta R_\mathrm {g}$ alone with uncertainties indicated by the shaded areas. |
| Tables | |
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Table 1:
Overview of the theoretical accuracy and ${\alpha _{S}^{\text {FSR}}(m_{{\mathrm {Z}}})}$ settings of the generator setups used for predicting the jet substructure. The acronym "nLL'' stands for approximate next-to-leading-log accuracy. |
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Table 2:
$\chi ^{2}$ values and the numbers of degrees of freedom (ndf) for the data-to-simulation comparison of the distributions of the four weakly-correlated jet substructure observables, $\lambda _{0}^{0}$ ($N$), $\varepsilon $, $z_\mathrm {g}$, and $\Delta R_\mathrm {g}$, for four different jet flavors and six MC generator setups. |
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Table 3:
$\chi ^{2}$ values and the numbers of degrees of freedom (ndf) for the data-to-simulation comparison of the distributions of the four weakly-correlated jet substructure observables, $\lambda _{0}^{0}$ ($N$), $\varepsilon $, $z_\mathrm {g}$, and $\Delta R_\mathrm {g}$, for four different jet flavors and seven POWHEG+PYTHIA-8 model variations. The value of the strong coupling is $ {\alpha _{S}^{\text {FSR}}(m_{{\mathrm {Z}}})} = $ 0.1365 for all predictions. |
| Summary |
|
A measurement of jet substructure observables in resolved $\mathrm{t\bar{t}}$ lepton+jets events from pp collisions at $\sqrt{s} = $ 13 TeV has been presented, including several variables relevant for quark-gluon discrimination and for heavy Lorentz-boosted object identification. The investigated observables provide valuable insights on the perturbative and nonperturbative phases of jet evolution. 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. Data are compared to theoretical predictions either based on next-to-leading-order (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 2 shower model. 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. With the default Monte Carlo (MC) generator tunes, none of the predictions yields a good overall reproduction of the experimental distributions. Thus, some further tuning of the models is required, with special attention to the data/MC disagreement observed in the particle multiplicity $\lambda_0^0$ and correlated observables, including those designed for quark/gluon discrimination. The groomed momentum fraction $z_\mathrm{g}$ is directly sensitive to the parton-shower splitting functions, thereby providing a useful handle to improve their modeling in the MC generators. The angle between the groomed subjets, $\Delta R_\mathrm{g}$, is a powerful observable for extracting the value of the strong coupling in final-state parton radiation (FSR) processes. A value of ${\alpha_{S}(m_{\mathrm{Z}})} = $ 0.115$^{+0.015}_{-0.013}$ including experimental as well as model uncertainties, has been extracted at leading-order plus leading-log accuracy, where the precision is limited by the FSR scale uncertainty of the PYTHIA 8 prediction. Besides tuning and improving final-state parton showers, the present data also provide useful tests for improved quantum chromodynamics analytical calculations, including higher-order fixed and logarithmic corrections, for infrared- and/or collinear-safe observables. |
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