Wide-angle photo- and electroproduction of pions to twist-3 accuracy

TL;DR

This paper analyzes wide-angle pion photo- and electroproduction using a twist-3 accurate handbag mechanism, incorporating both 2- and 3-body Fock components to ensure gauge invariance, and compares results with experimental data.

Contribution

It introduces a comprehensive twist-3 calculation of pion production amplitudes, including both Fock components, to improve theoretical predictions and gauge invariance in QED and QCD.

Findings

Agreement with experimental data on charged pion photoproduction

Predictions for electroproduction and spin effects

Complete twist-3 subprocess amplitudes for pion electroproduction

Abstract

We investigate wide-angle photo- and electroproduction of pions within the handbag mechanism in which the $\gamma^{(*)} N\to \pi N'$ amplitudes factorize into hard partonic subprocess amplitudes, $\gamma^{(*)} q\to \pi q'$, and form factors representing $1/x$-moments of generalized parton distributions (GPDs). The subprocess is calculated to twist-3 accuracy taking into account the 2- and 3-body Fock components of the pion. Both components are required for achieving gauge invariance in QED and QCD. The twist-2 and twist-3 distribution amplitudes (DAs) of the pion as well as the form factors are taken from our study of $\pi^0$ photoproduction. Extensive results on photoproduction of charged pions are presented and compared to experiment. Predictions on electroproduction of pions as well as on spin effects are also given. As a byproduct of our analysis we also obtain the complete twist-3 subprocess amplitudes contributing to deeply-virtual electroproduction of pions.