Single-Proton Emission Following Positive Pion Absorption in Carbon

Abstract

Pions are usually absorbed by a pair of nucleons in complex nuclei. It is, however, possible for the pion to be absorbed by a single nucleon, leading to the emission of only one nucleon. Letourneux and Eisenberg have pointed out that this latter reaction would be useful in studying single-nucleon states within nuclei and as a test of the validity of perturbation theory for low-energy pion-nucleus interactions. Accordingly, we have searched for the reaction ${\mathrm{C}}^{12}({\ensuremath{\pi}}^{+}, p){\mathrm{C}}^{11}$ at 68-MeV pion energy and 11\ifmmode^\circ\else\textdegree\fi{} proton emission angle. The observed cross section of 640\ifmmode\pm\else\textpm\fi{}130 \ensuremath{\mu}b/sr for absorption by $1{p}_{\frac{3}{2}}$ neutrons is more than eight times larger than the theoretical value.