Electroproduction of π+ from 12C leading to low-lying residual states in 12B

Abstract

Energy distributions of π + produced from 12C by electrons of total energy 195 MeV were measured at various angles. The results show large contributions from transitions leaving the residual nucleus in the ground (1 +), first (2 +) excited state and states at around 4.5 MeV. The angular distributions of 12C( γ, π +) 12B leading to these residual states are deduced from the energy distributions by the unfolding method with the virtual photon theory. Theoretical results with the Helm model and the shell model are compared with the experimental results. Their relative shapes are in good agreement. A better agreement in the absolute value is found for the theoretical results which include the final-state interaction estimated with a pion optical potential. The surface production model shows better agreement with the experimental ( γ, π +) cross sections than the volume production model.