Twist-3 contributions to wide-angle photoproduction of pions

Abstract

We investigate wide-angle π 0 photoproduction within the handbag approach to twist-3 accuracy. In contrast to earlier work both the 2-particle as well as the 3-particle twist-3 contributions are taken into account. It is shown that both are needed for consistent results that respect gauge invariance and crossing properties. The numerical studies reveal the dominance of the twist-3 contribution. With it fair agreement with the recent CLAS measurement of the π 0 cross section is obtained. We briefly comment also on wide-angle photoproduction of other pseudoscalar mesons.

Probing axial quark generalized parton distributions through exclusive photoproduction of a γπ± pair with a large invariant mass

“…The problem of collinear factorization at the twist 3 level is not yet fully understood. Despite several successful attempts to include consistently such effects in exclusive amplitudes [23,24,25,26], the existing model for explaining pion electroproduction data go beyond standard collinear factorization [27,28]. Although one may expect sizable contributions to our present process due to the twist 3 pion DA, we are lacking a consistent framework to study this contribution.…”

Hard exclusive processes involving kaons

“…It would be interesting to go beyond this approximation and to include both the two-and three-body twist-3 contributions. In wide-angle photoproduction of pions at least these contributions play an important role [40]. In contrast to previous studies of hard processes involving pseudoscalar mesons the evolution of the transversity GPDs is taken into account.…”

Wide-angle photo- and electroproduction of pions to twist-3 accuracy

“…This singularity has been regularized in [10,11] by keeping the quark transverse momentum in the propagators. More details on the twist-3 contribution in the DVMP limit will be given in a forthcoming paper [35].…”