CMS-PAS-BPH-15-003 | ||

Measurements of correlations between J/$\psi$ mesons and jets produced in $\sqrt{s}= $ 8 TeV pp collisions | ||

CMS Collaboration | ||

May 2019 | ||

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Abstract:
A study of the production of J/$\psi$ mesons in conjunction with jets in pp collisions at $\sqrt{s} = $ 8 TeV is presented. The analysis is based on data corresponding to an integrated luminosity of 19.1 fb$^{-1}$ collected with the CMS detector at the LHC. For events with at least one observed jet, the angular separation between the J/$\psi$ meson and the jet is used to test whether the J/$\psi$ meson is a jet fragment. The differential distributions of jet fragmentation probability as a function of jet energy for a fixed J/$\psi$ energy fraction $z$ are presented. The experimental results are compared to a theoretical model using the fragmenting jet function (FJF) approach. The J/$\psi$ jet fragmentation data agree with the predictions of the FJF calculations that use specific long-distance matrix element parameters. This agreement shows that the combination of data on jet fragmentation to J/$\psi$ mesons and FJF analysis is a new way to test predictions for charmonium production from nonrelativistic quantum chromodynamics and to evaluate long-distance matrix element parameter sets. The analysis also shows that most J/$\psi$ mesons with energy above 15 GeV and rapidity $|y| < $ 1.0 are fragments of jets with pseudorapidity $|\eta_{\mathrm{jet}}| < $ 1.
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PLB 804 (2020) 135409.The superseded preliminary plots can be found here. |

Figures | |

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Figure 1:
Left: The $\Delta $R for J/$\psi$ events with one observed jet. Right: The $\Delta R_1$ vs. $\Delta R_2$ for two-jet events, where $\Delta R_1$ is associated with the higher-energy jet and $\Delta R_2$ with the lower-energy jet. |

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Figure 1-a:
The $\Delta $R for J/$\psi$ events with one observed jet. |

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Figure 1-b:
The $\Delta R_1$ vs. $\Delta R_2$ for two-jet events, where $\Delta R_1$ is associated with the higher-energy jet and $\Delta R_2$ with the lower-energy jet. |

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Figure 2:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1$ = 0.425, using: (left) the BCKL LDME set [18]; and (right) the BK LDME set [17]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

png pdf |
Figure 2-a:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1$ = 0.425, using the BCKL LDME set [18]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

png pdf |
Figure 2-b:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1$ = 0.425, using the BK LDME set [17]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

png pdf |
Figure 3:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1= $ 0.525, using: (left) the BCKL LDME set [18]; and (right) the BK LDME set [17]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

png pdf |
Figure 3-a:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1= $ 0.525, using the BCKL LDME set [18]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

png pdf |
Figure 3-b:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1= $ 0.525, using the BK LDME set [17]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

png pdf |
Figure 4:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1 = $ 0.625, using: (left) the BCKL LDME set [18]; and (right) the BK LDME set [17]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

png pdf |
Figure 4-a:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1 = $ 0.625, using the BCKL LDME set [18]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

png pdf |
Figure 4-b:
Comparison of data (closed circles with vertical bars representing the statistical uncertainty (inner bars) and total uncertainty (outer bars)) with the four LDME terms for $z_1 = $ 0.625, using the BK LDME set [17]. The curves show the jet energy dependence of the FJF model predictions, from which the averages were calculated. |

Tables | |

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Table 1:
The values of the $\chi ^2$ and the $\chi ^2$ probability (in parentheses) for 7 degrees of freedom in the comparison of the data and the FJF prediction for each LDME term with $z_1$ = 0.425. |

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Table 2:
The values of the $\chi ^2$ and the $\chi ^2$ probability (in parentheses) for 7 degrees of freedom in the comparison of the data and the FJF prediction for each LDME term with $z_1$ = 0.525. |

png pdf |
Table 3:
The values of the $\chi ^2$ and the $\chi ^2$ probability (in parentheses) for 7 degrees of freedom in the comparison of the data and the FJF prediction for each LDME term with $z_1 = $ 0.625. |

Summary |

The first analysis comparing data for J/$\psi$ mesons produced as fragmentation products of a central gluonic jet with a theoretical analysis based on Fragmenting Jet Function (FJF) approach has been presented. The data were collected by the CMS Collaboration from $\mathrm{pp}$ collisions at $\sqrt{s}= $ 8 TeV, corresponding to an integrated luminosity of 19.1 fb$^{-1}$. The agreement between the data and the FJF predictions over a wide range of $z$, where $z$ is the J/$\psi$ fraction of the jet energy, validates the FJF approach for gluon fragmentation. For the three $z$ values, 0.425, 0.525, and 0.625, the nonrelativistic quantum chromodynamic long-distance matrix element (LDME) terms for the $^{3}S_{1}^{(8)}$ and $^3P_{J}^{(8)}$ configurations are not dominant for either the Bodwin, Chung, Kim and Lee (BCKL) [18] or Butenschoen and Kniehl (BK) [17] parameter sets, ie, these terms are not the main contributors to J/$\psi$ production by jet fragmentation. For the BCKL LDME parameters, the $^{1}S_{0}^{(8)}$ term dominates jet fragmentation to J/$\psi$ for all three $z$ values studied. This could explain the small J/$\psi$ polarization at large ${p_{\mathrm{T}}}$ observed in high energy hadronic collisions at the Tevatron and LHC. However, the possible role of the $^{3}S_{1}^{(1)}$ term using the BK parameters, with its implied large J/$\psi$ polarization, has to be addressed theoretically. It has almost the same jet energy dependence as the BCKL $^{1}S_{0}^{(8)}$ term for $z > $ 0.5, but not for lower $z$. For events with one observed jet, 84% of J/$\psi$ mesons with $E > $ 15 GeV and $|y| < $ 1 are fragments of a jet produced in the angular region $|\eta| < $ 1.0. We have also demonstrated that some J/$\psi$ mesons are fragments of jets that fail the requirement ${p_{\mathrm{T}}}|_{\mathrm{jet}} > $ 25 GeV. Using a simple model to estimate the fraction of J/$\psi$ mesons that are fragments of unobserved jets, we find that jet fragmentation can be the source of $ > $ 80% of the J/$\psi$ mesons produced in this kinematic region. |

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