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| CMS-SMP-16-014 ; CERN-EP-2017-290 | ||
| Azimuthal correlations for inclusive 2-jet, 3-jet, and 4-jet events in pp collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| 14 December 2017 | ||
| Eur. Phys. J. C 78 (2018) 566 | ||
| Abstract: Azimuthal correlations between the two jets with the largest transverse momenta $ {p_{\mathrm{T}}} $ in inclusive 2-, 3-, and 4-jet events are presented for several regions of the leading jet $ {p_{\mathrm{T}}} $ up to 4 TeV. For 3- and 4-jet scenarios, measurements of the minimum azimuthal angles between any two of the three or four leading $ {p_{\mathrm{T}}} $ jets are also presented. The analysis is based on data from proton-proton collisions collected by the CMS Collaboration at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Calculations based on leading-order matrix elements supplemented with parton showering and hadronization do not fully describe the data, so next-to-leading-order calculations matched with parton shower and hadronization models are needed to better describe the measured distributions. Furthermore, we show that azimuthal jet correlations are sensitive to details of the parton showering, hadronization, and multiparton interactions. A next-to-leading-order calculation matched with parton showers in the MC@NLO method, as implemented in HERWIG 7, gives a better overall description of the measurements than the POWHEG method. | ||
| Links: e-print arXiv:1712.05471 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Normalized inclusive 2-jet cross section differential in $ {\Delta \phi _\text {1,2}} $ for nine $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions, scaled by multiplicative factors for presentation purposes. The size of the data symbol includes both statistical and systematic uncertainties. The data points are overlaid with the predictions from the PH-2J + PYTHIA 8 event generator. |
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Figure 2:
Normalized inclusive 3-jet cross section differential in $ {\Delta \phi _\text {1,2}} $ for eight $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions, scaled by multiplicative factors for presentation purposes. The size of the data symbol includes both statistical and systematic uncertainties. The data points are overlaid with the predictions from the PH-2J + PYTHIA 8 event generator. |
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Figure 3:
Normalized inclusive 4-jet cross section differential in $ {\Delta \phi _\text {1,2}} $ for eight $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions, scaled by multiplicative factors for presentation purposes. The size of the data symbol includes both statistical and systematic uncertainties. The data points are overlaid with the predictions from the PH-2J + PYTHIA 8 event generator. |
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Figure 4:
Ratios of PYTHIA 8, HERWIG++, and MadGraph + PYTHIA 8 predictions to the normalized inclusive 2-jet cross section differential in $ {\Delta \phi _\text {1,2}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties in the simulated data. |
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Figure 5:
Ratios of PYTHIA 8, HERWIG++, and MadGraph + PYTHIA 8 predictions to the normalized inclusive 3-jet cross section differential in $ {\Delta \phi _\text {1,2}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties in the simulated data. |
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Figure 6:
Ratios of PYTHIA 8, HERWIG++, and MadGraph + PYTHIA 8 predictions to the normalized inclusive 4-jet cross section differential in $ {\Delta \phi _\text {1,2}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties in the simulated data. |
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Figure 7:
Ratios of PH-2J + PYTHIA 8, PH-2J + HERWIG++, PH-2J + PYTHIA 8, and HERWIG 7 predictions to the normalized inclusive 2-jet cross section differential in $ {\Delta \phi _\text {1,2}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties in the simulated data. |
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Figure 8:
Ratios of PH-2J + PYTHIA 8, PH-2J + HERWIG++, PH-2J + PYTHIA 8, and HERWIG 7 predictions to the normalized inclusive 3-jet cross section differential in $ {\Delta \phi _\text {1,2}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties in the simulated data. |
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Figure 9:
Ratios of PH-2J + PYTHIA 8, PH-2J + HERWIG++, PH-2J + PYTHIA 8, and HERWIG 7 predictions to the normalized inclusive 4-jet cross section differential in $ {\Delta \phi _\text {1,2}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties in the simulated data. |
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Figure 10:
Normalized inclusive 3-jet cross section differential in $ {\Delta \phi _\text {2j}^\text {min}} $ for eight $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions, scaled by multiplicative factors for presentation purposes. The size of the data symbol includes both statistical and systematic uncertainties. The data points are overlaid with the predictions from the PH-2J + PYTHIA 8 event generator. |
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Figure 11:
Normalized inclusive 4-jet cross section differential in $ {\Delta \phi _\text {2j}^\text {min}} $ for eight $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions, scaled by multiplicative factors for presentation purposes. The size of the data symbol includes both statistical and systematic uncertainties. The data points are overlaid with the predictions from the PH-2J + PYTHIA 8 event generator. |
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Figure 12:
Ratios of PYTHIA 8, HERWIG++, and MadGraph + PYTHIA 8 predictions to the normalized inclusive 3-jet cross section differential in $ {\Delta \phi _\text {2j}^\text {min}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties in the simulated data. |
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Figure 13:
Ratios of PYTHIA 8, HERWIG++, and MadGraph + PYTHIA 8 predictions to the normalized inclusive 4-jet cross section differential in $ {\Delta \phi _\text {2j}^\text {min}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties in the simulated data. |
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Figure 14:
Ratios of PH-2J + PYTHIA 8, PH-2J + HERWIG++, PH-2J + PYTHIA 8, and HERWIG 7 predictions to the normalized inclusive 3-jet cross section differential in $ {\Delta \phi _\text {2j}^\text {min}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties of the simulated data. |
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Figure 15:
Ratios of PH-2J + PYTHIA 8, PH-2J + HERWIG++, PH-2J + PYTHIA 8, and HERWIG 7 predictions to the normalized inclusive 4-jet cross section differential in $ {\Delta \phi _\text {2j}^\text {min}} $, for all $ {{p_{\mathrm {T}}} ^{\text {max}}} $ regions. The solid band indicates the total experimental uncertainty and the vertical bars on the points represent the statistical uncertainties of the simulated data. |
| Tables | |
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Table 1:
Monte Carlo event generators used for comparison in this analysis. Version of the generators, PDF set, underlying event tune, and corresponding references are listed. |
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Table 2:
The integrated luminosity for each trigger sample considered in this analysis. |
| Summary |
|
Measurements of the normalized inclusive 2-, 3-, and 4-jet cross sections differential in the azimuthal angular separation $ {\Delta\phi_\text{1,2}} $ and of the normalized inclusive 3- and 4-jet cross sections differential in the minimum azimuthal angular separation between any two jets $ {\Delta\phi_\text{2j}^\text{min}} $ are presented for several regions of the leading-jet transverse momentum $ {p_{\mathrm{T}}}^{\text{max}} $. The measurements are performed using data collected during 2016 with the CMS detector at the CERN LHC corresponding to an integrated luminosity of 35.9 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = $ 13 TeV. The measured distributions in $ {\Delta\phi_\text{1,2}} $ and $ {\Delta\phi_\text{2j}^\text{min}} $ are compared with predictions from PYTHIA 8, HERWIG++, MadGraph + PYTHIA 8, PH-2J matched to PYTHIA 8 and HERWIG++, PH-3J + PYTHIA 8, and HERWIG 7 event generators. The leading order (LO) PYTHIA 8 dijet event generator exhibits small deviations from the $ {\Delta\phi_\text{1,2}} $ measurements but shows significant deviations at low-$ {p_{\mathrm{T}}} $ in the $ {\Delta\phi_\text{2j}^\text{min}} $ distributions. The HERWIG++ event generator exhibits the largest deviations of any of the generators for the $ {\Delta\phi_\text{1,2}} $ measurements, but provides a reasonable description of the $ {\Delta\phi_\text{2j}^\text{min}} $ distributions. The tree-level multijet event generator MadGraph in combination with PYTHIA 8 for showering, hadronization, and multiparton interactions provides a good overall description of the measurements, except for the $ {\Delta\phi_\text{2j}^\text{min}} $ distributions in the 4-jet case, where the generator deviates from the measurement mainly at high $ {{p_{\mathrm {T}}} ^{\text {max}}} $. The dijet next-to-leading order (NLO) PH-2J event generator deviates from the $ {\Delta\phi_\text{1,2}} $ measurements, but provides a good description of the $ {\Delta\phi_\text{2j}^\text{min}} $ observable. The predictions from the three-jet NLO PH-3J event generator exhibit large deviations from the measurements and describe the considered multijet observables in a less accurate way than the predictions from PH-2J. Parton shower contributions are responsible for the different behaviour of the PH-2J and PH-3J predictions. Finally, predictions from the dijet NLO HERWIG 7 event generator matched to parton shower contributions with the MC@NLO method provide a very good description of the $ {\Delta\phi_\text{1,2}} $ measurements, showing improvement in comparison to HERWIG++. All these observations emphasize the need to improve predictions for multijet production. Similar observations, for the inclusive 2-jet cross sections differential in $ {\Delta\phi_\text{1,2}} $, were reported previously by CMS [5] at a different centre-of-mass energy of 8 TeV. The extension of $ {\Delta\phi_\text{1,2}} $ correlations, and the measurement of the $ {\Delta\phi_\text{2j}^\text{min}} $ distributions in inclusive 3- and 4-jet topologies are novel measurements of the present analysis. |
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