QCD factorization at fixed Q^2(1-x)

TL;DR

This paper discusses QCD factorization in exclusive processes at fixed Q^2(1-x), showing how amplitudes can be factorized into subprocesses and generalized parton distributions, with applications to the Drell-Yan process.

Contribution

It introduces a framework for factorizing amplitudes in exclusive processes at fixed Q^2(1-x) and relates inclusive cross sections to multiparton distributions.

Findings

Amplitudes factorize into subprocess and GPDs.

Inclusive cross sections relate to multiparton distributions.

Application explains virtual photon polarization in Drell-Yan.

Abstract

Amplitudes of hard {\it exclusive} processes such as \gamma^*(Q^2) N \to \gamma Y, where Y=N (DVCS) or any other state with a limited mass (M_Y^2 << Q^2), factorize into a hard subprocess amplitude and a target (transition) GPD. The corresponding {\it inclusive} cross section, summed over all states Y of a given (limited) mass, is then given by the discontinuity of a forward multiparton distribution. An application to the Drell-Yan process \pi^+ N \to \gamma^*(x_F,Q^2)+Y allows to explain the observed longitudinal polarization of the virtual photon at high x_F.