DOUBLE GIANT RESONANCES

A long-standing issue in nuclear structure is whether double giant resonances do exist. Exotic excitations like the double giant-dipole were predicted for many years but not observed experimentally until recently. Several experiments have been carried out at Los Alamos National Laboratory and other laboratories to search for these new collective modes of the nucleus. The results discover the existence of two previously unobserved types of double giant resonances. This work presents a review of the pion double charge exchange data and the analysis which support the existence of two such exotic vibrational nuclear modes: the giant dipole resonance built on the isobaric analog state and the double isovector giant-dipole resonance. Excitation of multiphonon states also becomes a very likely process in relativistic heavy-ion reactions where a direct identification of the double giant-dipole resonance has been reported recently.