First Monte Carlo Global QCD Analysis of Pion Parton Distributions.

Area of Science:

• High-energy particle physics
• Quantum Chromodynamics (QCD)
• Hadron structure

Background:

• Parton distribution functions (PDFs) describe the internal structure of hadrons.
• Previous analyses of pion PDFs relied heavily on Drell-Yan data, limiting insights at low momentum fractions.
• Understanding pion structure is crucial for interpreting high-energy scattering experiments.

Purpose of the Study:

• To perform the first global QCD analysis of pion PDFs by combining diverse experimental data.
• To determine pion PDFs with reduced model dependence, especially at small Bjorken-x.
• To investigate the momentum fraction carried by gluons and sea quarks in the pion.

Main Methods:

• Global Quantum Chromodynamics (QCD) analysis.
• Integration of πA Drell-Yan data with leading neutron electroproduction data from HERA.
• Application of a Monte Carlo approach utilizing nested sampling.

Main Results:

• Pion PDFs determined down to significantly lower values of x.
• Gluons found to carry a higher momentum fraction (~30%) in the pion compared to previous estimates.
• Sea quarks carry a smaller momentum fraction (~15%) at the input scale.

Conclusions:

• The combined analysis provides a more comprehensive picture of pion internal structure.
• The determined pion PDFs offer improved constraints for theoretical calculations and experimental interpretations.
• The framework can potentially describe flavor asymmetries in other hadrons, like the proton.