PIONIC DOUBLE-CHARGE-EXCHANGE ON N = Z DOUBLY CLOSED-SHELL NUCLEI

The (pi(+), pi(-)) reaction on the isoscalar, doubly magic nuclei O-16 and Ca-40 has been measured in the energy range T-pi = 45-90 MeV. The forward angle cross sections of the ground state transitions (GST) sh ow a very pronounced resonancelike energy dependence. The observed ene rgy and angle dependences are well described by the recent hypothesis of the formation of a pi NN resonance in the course of the double char ge exchange process. The deduced spreading widths are in accordance wi th estimates of the d' collision damping in the nuclear medium. In the reaction on O-16 in addition to the GST the transition to a 0(+) stat e at E-x = 2.1(2) MeV in Ne-16 has been-observed, which is interpreted as the quadruple isobaric analog state (QIAS) of the 0(2)(+) state in C-16 at E-x = 3.03 MeV.