Wide-angle photoproduction of the $\eta'$-meson and its gluon content

We investigate wide-angle photoproduction of the $\eta'$ meson within the handbag approach to twist-3 accuracy. It turns out that, due to the gluon content of the $\eta'$, this process is dominated by twist-2 in contrast with pion and $\eta$ photoproduction. Using the presently available information on the twist-2 and twist-3 distribution amplitudes and on the $\eta - \eta'$ mixing, we provide prediction for the $\eta'$ cross section and helicity correlations. It is argued that $\eta'$ photoproduction is well suited to improve our knowledge of the two-gluon distribution amplitude.
Comment: 18 pages, 5 figures