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Photoproduction of $η^\prime$ mesons off nuclei and their properties in the nuclear medium

We study the photoproduction of $η^\prime$ mesons from nuclei near the threshold within the collision model based on the nuclear spectral function. The model takes properly into account both primary photon-nucleon and secondary pion-nucleon $η^\prime$ production processes as well as the effect of the nuclear $η^\prime$ mean-field potential on these processes. We find that the secondary pion-induced reaction channel $πN \to {η^\prime}N$ plays an insignificant role in the $η^\prime$ photoproduction off nuclei. We calculate the transparency ratio for $eta^\prime$ mesons and compare it to the available experimental data. The comparison indicates an inelastic ${η^\prime}N$ cross section of the order of 6-10 mb. We show that the existing transparency ratio measurements do not allow one to distinguish between two adopted $η^\prime$ in-medium modification scenarios. Our studies also demonstrate that the momentum distribution and excitation function for $η^\prime$ production in $γA$ reactions reveal some sensitivity to these scenarios, which means that such observables may be an important tool to get a valuable information on the $η^\prime$ in-medium properties.