NRQCD Confronts LHCb Data on Quarkonium Production within Jets

Area of Science:

• High Energy Physics
• Quantum Chromodynamics (QCD)
• Particle Physics

Background:

• The production of heavy quarkonium states, such as the J/ψ meson, within jets is a complex phenomenon in high-energy particle collisions.
• Previous simulations using default Pythia models showed poor agreement with LHCb measurements of the J/ψ momentum fraction within jets.

Purpose of the Study:

• To analyze the LHCb measurement of the J/ψ momentum fraction within jets.
• To compare LHCb data with theoretical calculations using the fragmenting jet function (FJF) formalism and nonrelativistic QCD (NRQCD).
• To investigate the role of different extractions of nonperturbative NRQCD long-distance matrix elements (LDMEs).

Main Methods:

• Analytic calculations employing the fragmenting jet function (FJF) formalism with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution.
• Convolution of hard QCD partonic cross sections (calculated with MadGraph) and Pythia-showered events with leading-order NRQCD fragmentation functions.
• Comparison of theoretical predictions with LHCb experimental data for the z(J/ψ) distribution.

Main Results:

• Both FJF and NRQCD calculations provide reasonable agreement with the LHCb measured z(J/ψ) distribution.
• Theoretical predictions show significant improvement over default Pythia simulations.
• NRQCD calculations exhibit good agreement with LHCb data, irrespective of the LDME fit used, particularly those derived from high-transverse-momentum collider data.

Conclusions:

• The fragmenting jet function formalism and NRQCD provide a more accurate description of J/ψ production in jets compared to default Pythia.
• The study highlights the importance of nonperturbative NRQCD matrix elements and their accurate extraction for understanding heavy quarkonium production.
• Collider data, especially at high transverse momentum, offers crucial constraints for LDME fits, leading to improved theoretical predictions.