A QCD analysis of \bar p N -> gamma^* pi and \bar p N -> gamma^* gamma. Where is the pion in the proton ?

TL;DR

This paper investigates the nucleon-antinucleon annihilation processes involving virtual photons and mesons, analyzing the internal structure of the proton through transition distribution amplitudes in the scaling regime.

Contribution

It introduces a factorization framework for these annihilation processes using transition distribution amplitudes, revealing the proton's internal transverse structure.

Findings

Factorization of amplitude into distribution amplitude, short-distance matrix element, and TDA.

Mapping of the proton's internal transverse locations of core and cloud.

Application to nucleon-antinucleon annihilation into virtual photons and mesons.

Abstract

We study the scaling regime of nucleon-anti-nucleon annihilation into a deeply virtual photon and a photon or meson, \bar p N -> gamma ^* pi, \bar p N -> gamma ^* gamma, in the forward direction. The leading twist amplitude factorizes into an antiproton distribution amplitude, a short-distance matrix element and a long-distance dominated transition distribution amplitude (TDA) which describes the nucleon to meson or photon transition. The impact representation of this TDA maps out the transverse locations of the small size core and the meson or photon cloud inside the proton.