Angular distributions of the $\frac{{\pi }^{-}}{{\pi }^{+}}$ ratio for 15.8 and 17.9 MeV pions have been measured from the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$$(e,e^{\prime }{\pi }^{\pm })X$ reaction at incident electron energy of 200 MeV. The results show a structure with a minimum at ${\theta }_{\pi }\simeq 100°$. Calculations based on the partial conservation of axial-vector current hypothesis and realistic optical potentials fail to reproduce the experimental structure.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$($e$,$e^{\prime }{\pi }^{\pm }$), $E_e=200\mathrm{}$ MeV; measured $\sigma (E_{{\pi }^{\pm }},\theta )$, $E_{{\pi }^{\pm }}=15.8, 17.9$ MeV; calculated $R=\sigma \left({\pi }^{\pm }\right)$ with (PCAP) derived amplitudes; calculated $\frac{\left[\sigma \right(\gamma n\to p{\pi }^{-}\left)\right]}{\left[\sigma \right(\gamma p\to n{\pi }^{+}\left)\right]}$ with momentum dependent terms.

• Received 15 June 1981

DOI:https://doi.org/10.1103/PhysRevC.25.1562