Isospin splitting in analog giant resonances excited by single pion charge exchange reactions

Abstract

Giant isovector analog E1 resonances have been observed by means of the pion single-charge-exchange reactions ( π ±, π 0). The giant T = 1 analog E1 resonances in 12B and 12N, built on the ground state of 12C, were observed in the 12C( π ±, π 0) reactions. The giant T = 3 2 resonances in 13B and 9Li, built on the ground states of 13C and 9Be, were studied with the 13C, 9Be( π −, π 0) reactions, respectively. Analogs of these resonances were found in the 13C, 9Be( π +, π 0) reactions along with lower lying T = 1 2 resonances. These resonances together with the higher T = 3 2 resonances constitute isospin-splitting in the nuclei, 13N and 9B. These isospin assignments were made by comparing results from the ( π ±, π 0) reactions and their measured angular distributions. The assignments were confirmed by determining the decay properties of the resonances with coincident ( π 0p) measurements in the ( π +, π 0p) reactions. The proton angular distributions measured relative to the momentum transfer direction were consistent with a dipole process.