Experimental test of virtual photon theory for pion electroproduction on light nuclei

The virtual photon spectrum shape and intensity within several MeV of the kinematic limit was measured for ${}_{}{}^9{}_{}{}^{}\mathrm{Be}(e, {\pi }^{+}){}_{}{}^9{}_{}{}^{}\mathrm{Li}, e^{\prime }$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}(e, {\pi }^{+}){}_{}{}^{16}{}_{}{}^{}\mathrm{N}, e^{\prime }(T_{\pi }=28\mathrm{} \mathrm{MeV}, {\theta }_{\pi }=90\mathrm{}°)$. The intensity over this interval is 1.25±0.10 times plane-wave virtual photon theory predictions; the shape agrees with theory within errors. Measurements on the proton 30 to 55 MeV below the end point agree with the intensity predictions of virtual photon theory within the errors (±8%).