Backward-angle electroproduction of ${\eta }^{\mathrm{\prime }}$ mesons off protons at $W=2.13\text{ GeV}$ and $Q^2=0.46{\left(\text{GeV}\mathrm{/}c\right)}^2$

The electroproduction of ${\eta }^{\mathrm{\prime }}$ mesons from a ${}^1\mathrm{H}$ target at $W=2.13\text{ GeV}$, $Q^2=0.46{\left(\text{GeV}\mathrm{/}c\right)}^2$ and $\cos {\theta }_{{\gamma }^{\ast }{\eta }^{\mathrm{\prime }}}^{\text{CM}}\approx -1$ has been experimentally measured. The differential cross section of virtual-photoproduction has been obtained as $4.4\pm 0.8\left(\text{stat.}\right)\pm 0.4\left(\text{sys.}\right)\text{ nb/sr}$ in the One-Photon-Exchange Approximation. This value is one-sixth of that of real-photoproduction at backward angles. A comparison with newly-developed isobar model calculations not only shows validity of the theoretical framewark employed, but also imposes new constrains on coupling strength between the ${\eta }^{\mathrm{\prime }}p$ final state and nucleon resonances.