Hard exclusive production of two pions: Dipion mass distributions in gamma* N -->pi pi N and gamma* gamma --> pi pi

TL;DR

This paper proposes a leading twist parametrization for dipion mass distributions in hard exclusive reactions, linking it to quark distributions and meson distribution amplitudes, and highlights how measurements can reveal pion's partonic structure.

Contribution

It introduces a new leading twist model for dipion mass distributions in exclusive reactions, connecting them to pion quark distributions and meson distribution amplitudes.

Findings

Parametrization relates dipion mass distribution to quark distributions.

Measurement of dipion shape informs about pion's partonic structure.

Expression for gamma* gamma to pi pi amplitude near threshold is provided.

Abstract

The leading twist parametrization of dipion mass distribution in hard exclusive reactions is proposed. Its parameters are related to quark distributions (usual and skewed) in the pion and to distributions amplitudes of mesons ($\pi$, $\rho$, etc.). We show that measurements of the shape of dipion mass distribution in hard exclusie reactions can give important information about partonic structure of the pion. The expression for the amplitude of the reaction $\gamma^*\gamma\to \pi\pi$ near the threshold in terms of singlet quark distribution in the pion is presented.