Pion structure in QCD: From theory to lattice to experimental data

TL;DR

This paper reviews the current understanding of the pion distribution amplitude in QCD, integrating nonperturbative sum rules, experimental data analysis, and lattice QCD calculations, and compares theoretical predictions with experimental measurements.

Contribution

It combines multiple approaches to analyze the pion DA, introduces an improved nonlocal condensate model, and provides predictions for related form factors and Drell-Yan processes.

Findings

Consistent pion DA predictions from sum rules, lattice QCD, and experimental data.

Agreement between QCD-based predictions and JLab measurements of the pion form factor.

Enhanced understanding of nonlocal condensates' impact on pion structure.

Abstract

We describe the present status of the pion distribution amplitude (DA) as it originates from several sources: (i) a nonperturbative approach based on QCD sum rules with nonlocal condensates, (ii) an $O(\alpha_s)$ QCD analysis of the CLEO data on F^{\gamma\gamma^*\pi}(Q^2) with asymptotic and renormalon models for higher twists, and (iii) recent high-precision lattice QCD calculations of the second moment of the pion DA. We show predictions for the pion electromagnetic form factor, obtained in analytic QCD perturbation theory, and compare it with the JLab data on F_{\pi}(Q^2). We also discuss in this context an improved model for nonlocal condensates in QCD and show its consequences for the pion DA and the \gamma\gamma^*\to\pi transition form factor. We include a brief analysis of meson-induced massive lepton (muon) Drell--Yan production for the process \pi^{-}N\to\mu^{+}\mu^{-}X, considering both an unpolarized nucleon target and longitudinally polarized protons.