Complete Nonrelativistic-QCD Prediction for Prompt Double J/ψ Hadroproduction.

Area of Science:

• High Energy Physics
• Quantum Chromodynamics
• Particle Phenomenology

Background:

• Prompt double J/ψ hadroproduction is a key process for testing Quantum Chromodynamics (QCD).
• Previous theoretical models, primarily using the color-singlet model, failed to fully explain experimental measurements.
• The nonrelativistic-QCD (nrQCD) factorization framework offers a more comprehensive approach.

Purpose of the Study:

• To conduct a complete leading-order study of prompt double J/ψ hadroproduction.
• To investigate the contributions of all relevant cc̅ Fock states within the nrQCD framework.
• To reconcile theoretical predictions with recent experimental data from the Large Hadron Collider (LHC).

Main Methods:

• Application of the nonrelativistic-QCD factorization framework.
• Inclusion of all possible pairings of cc̅ Fock states: (1)S(0)([8]), (3)S(1)([1,8]), and (3)P(J)([1,8]) with J=0,1,2.
• Leading-order calculations for J/ψ and χ(cJ) production.

Main Results:

• Previously overlooked color-octet channels, specifically (1)S(0)([8]) and (3)P(J)([8]) for J/ψ, and (3)P(J)([1]) and (3)S(1)([8]) for χ(cJ), were found to dominate at large invariant masses and rapidity separations.
• The inclusion of these channels significantly reduces the discrepancy between theoretical predictions and CMS Collaboration data.
• The results suggest that the color-singlet model alone is insufficient.

Conclusions:

• The inclusion of dominant color-octet contributions is crucial for accurate theoretical descriptions of prompt double J/ψ hadroproduction.
• This comprehensive study brings theoretical predictions closer to experimental observations at the LHC.
• Further refinements may require incorporating next-to-leading-order corrections.