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The production of $\eta^\prime$ mesons in coincidence with forward-goingprotons has been studied in photon-induced reactions on $^{12}$C and on aliquid hydrogen (LH$_2$) target for incoming photon energies of 1.3-2.6 GeV atthe electron accelerator ELSA. The $\eta^\prime$ mesons have been identifiedvia the $\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma$ decayregistered with the CBELSA/TAPS detector system. Coincident protons have beenidentified in the MiniTAPS BaF$_2$ array at polar angles of $2^{\circ} \le\theta _{p} \le 11^{\circ}$. Under these kinematic constraints the$\eta^\prime$ mesons are produced with relatively low kinetic energy ($\approx$150 MeV) since the coincident protons take over most of the momentum of theincident-photon beam. For the C-target this allows the determination of thereal part of the $\eta^\prime$-carbon potential at low meson momenta bycomparing with collision model calculations of the $\eta^\prime$ kinetic energydistribution and excitation function. Fitting the latter data for $\eta^\prime$mesons going backwards in the center-of-mass system yields a potential depth ofV = $-$(44 $\pm$ 16(stat)$\pm$15(syst)) MeV, consistent with earlierdeterminations of the potential depth in inclusive measurements for average$\eta^\prime$ momenta of $\approx$ 1.1 GeV/$c$. Within the experimentaluncertainties, there is no indication of a momentum dependence of the$\eta^\prime$-carbon potential. The LH$_2$ data, taken as a reference to checkthe data analysis and the model calculations, provide differential and integralcross sections in good agreement with previous results for $\eta^\prime$photoproduction off the free proton.

The {\eta}'-carbon potential at low meson momenta