  Excitation spectra of $^{11}$C were measured in the $^{12}$C$(p,d)$ reaction
near the $\eta'$ emission threshold. A proton beam extracted from the
synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinged on a
carbon target. The momenta of deuterons emitted at 0 degrees were precisely
measured with the fragment separator FRS operated as a spectrometer. In
contrast to theoretical predictions on the possible existence of deeply bound
$\eta'$ mesic states in carbon nuclei, no distinct structures were observed
associated with the formation of bound states. The spectra were analyzed to set
stringent constraints on the formation cross section and on the hitherto
barely-known $\eta'$-nucleus interaction.
