E. R. Siciliano

Study of isovector resonances with pion charge exchange

Abstract Studies with the pion charge exchange reactions ( π ± , π 0 ) at 164 MeV using the π 0 spectrometer are yielding new results on the existence and systematic features of isovector resonances in nuclei. These experiments possess an unusually high signal/background ratio for isovector resonances of low-multipolarity. Results obtained to date are: (1) Observation and angular distribution measurement of the giant dipole resonances in nuclei 12 C, 40 Ca, 90 Zr and 120 Sn; (2) Observation and angular distribution measurements in the (π − , π 0 ) reaction on 90 Zr and 120 Sn of large signals possessing the expected angular distribution shapes and magnitudes for the isovector monopole resonance. Excitation energies are near the hydrodynamical model values 170 A − 1 3 MeV . Differential cross sections are approximately 0.7 J 2 (qR) mb/sr. An overview of this experimental program, with emphasis on new results, and how they correlate with existing knowledge on the isovector resonances, is given.