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.
Highlights
Hard exclusive processes have attracted much attention in recent years
The basis of the theoretical treatment of these processes is the representation of the amplitudes as a convolution of a hard partonic subprocess and soft hadronic matrix elements, parametrized as generalized parton distributions (GPDs) [1,2]
Besides the deeply virtual processes wide-angle ones have been investigated for which the hard scale is provided by a large momentum transfer from the photon to the meson
Summary
Hard exclusive processes have attracted much attention in recent years. The main interest has been focused on the deeply virtual processes for which the virtuality of the photon provides the hard scale. An attempt [9] to improve this (twist-2) analysis by taking into account twist-3 contributions in the Wandzura-Wilczek (WW) approximation, i.e., with only the qq Fock component of the pion considered, failed too—the twist-3 contribution in WW approximation is zero in wide-angle photoproduction of pions This is in sharp contrast to DVMP where the WW approximation is nonzero [10,11] and plays an important role in the interpretation of the data on deeply virtual pion electroproduction [12,13,14]. We apply the handbag mechanism to twist-3 accuracy to wide-angle photoproduction of charged pions and, in addition, we investigate wide-angle electroproduction of pions The latter process with its large variety of observables may allow for a detailed study of the dynamics of this process and to fix the pion DAs and form factors in detail. In an Appendix we compile the familiar evolution properties of the DAs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
