QCD factorization at fixed Q^2(1-x)
arXiv:0903.4962
Abstract
Amplitudes of hard {\it exclusive} processes such as γ^*(Q^2) N \to γY, 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 π^+ N \to γ^*(x_F,Q^2)+Y allows to explain the observed longitudinal polarization of the virtual photon at high x_F.
Talk at Epiphany meeting in commemoration of Jan Kwiecinski, Krakow, January 2009. 12 pages, 6 figures