New vistas of the meson structure in QCD from low to high energies

TL;DR

This paper reviews the quark structure of the pion in QCD, comparing theoretical models with experimental data and lattice computations, and predicts azimuthal asymmetries in polarized Drell-Yan processes.

Contribution

It provides a comprehensive analysis of pion structure across energy scales, integrating experimental results, lattice QCD calculations, and phenomenological predictions.

Findings

Experimental data supports certain pion distribution amplitude models.

Lattice computations of the pion's second moment show good agreement with theory.

Predictions for azimuthal asymmetry vary with different pion distribution amplitudes.

Abstract

This talk presents issues pertaining to the quark structure of the pion within QCD, both from the theoretical and from the experimental point of view. We review and discuss the pion-photon transition form factor and the pion's electromagnetic form factor vs. corresponding experimental data from the CLEO Collaboration and the JLab. We also examine the extent to which recent high-precision lattice computations of the second moment of the pion's distribution amplitude conform with theoretical models. Finally, we include predictions for the azimuthal asymmetry of the $\mu^+$ distribution in the polarized $\mu$-pair-induced DY production employing various pion distribution amplitudes.