Angular Distributions for the Reaction O18 ( π+ , π− ) Ne18 and Pion Double-Charge-Exchange Form Factors

The first angular distributions for pion double charge exchange to discrete nuclear states are reported. The analog and nonanalog states are found to be equally strongly populated. The direct, surface-dominated nature of the reaction is clearly demonstrated by the angular distribution shapes. It is shown that in order to produce detailed agreement with the data, the present ideas for the pion charge-exchange form factors may need to be drastically revised.