Abstract
We investigate wide-angle pi^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 pi^0 cross section is obtained. We briefly comment also on wide-angle photoproduction of other pseudoscalar mesons.
Highlights
Since 1996 there have been a lot of activities on the field of hard exclusive processes in conjunction with handbag factorization
A vast amount of data on such processes has been accumulated from HERMES, COMPASS, BABAR, and BELLE and from experiments performed at Jefferson Lab and HERA
There are reasonable arguments [1,2] that for large Mandelstam variables, s, −t, and −u, the Compton amplitudes can be represented as a product of amplitudes for the subprocess, Compton scattering off quarks, and form factors that represent 1=x moments of generalized parton distributions (GPDs)
Summary
Since 1996 there have been a lot of activities on the field of hard exclusive processes in conjunction with handbag factorization. The same situation appears in both hard π0 electroproduction and wide-angle π0 photoproduction—a leading-twist analysis fails badly in comparison with experiment at presently available hard scales In view of these experimental and theoretical results on hard exclusive pion electroproduction a resumption of the investigation on the wide-angle meson photoproduction seems to be appropriate, and this is the purpose of the present work. It differs from the earlier work [5,6] by the inclusion of the full, genuine twist-3 contribution, i.e., its 2-particle as well as its 3-particle parts. The separate 2- and 3-particle twist-3 subprocess amplitudes are presented in Appendix B
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