First Monte Carlo global QCD analysis of pion parton distributions

TL;DR

This paper presents the first comprehensive Monte Carlo global analysis of pion parton distribution functions, integrating Drell-Yan and HERA data to better understand pion structure and its implications for proton asymmetry.

Contribution

It introduces a novel global QCD analysis combining multiple data sources to determine pion PDFs with reduced model dependence and extended kinematic reach.

Findings

Gluons carry about 30% of pion momentum.

Sea quarks carry approximately 15% of pion momentum.

Analysis explains the proton's $ar d-ar u$ asymmetry within the same framework.

Abstract

We perform the first global QCD analysis of parton distribution functions (PDFs) in the pion, combining $\pi A$ Drell-Yan data with leading neutron electroproduction from HERA within a Monte Carlo approach based on nested sampling. Inclusion of the HERA data allows the pion PDFs to be determined down to much lower values of $x$, with relatively weak model dependence from uncertainties in the chiral splitting function. The combined analysis reveals that gluons carry a significantly higher pion momentum fraction, $\sim 30\%$, than that inferred from Drell-Yan data alone, with sea quarks carrying a somewhat smaller fraction, $\sim 15\%$, at the input scale. Within the same effective theory framework, the chiral splitting function and pion PDFs can be used to describe the $\bar d-\bar u$ asymmetry in the proton.