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

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