Modeling double charge exchange processes occurring in heavy ion reactions

Heavy ion induced double charge exchange reactions are treated as an incoherent sequence of two reactions driven by the exchange of charged mesons (double single charge exchange, DSCE). The process is described within a fully quantum mechanical distorted wave 2-step theory (2nd order DWBA). The DSCE reaction amplitudes are shown to be separable into super-positions of distortion factors, accounting for initial and final state ion-ion elastic interactions, and nuclear matrix elements (NMEs). Explicit expressions of projectile and target NMEs are derived within the QRPA theory. Reduction schemes for the DSCE transition form factors are described, analizing their momentum structure within the closure approximation. Formal analogies between the NMEs involved in DSCE reactions and in double beta decays are also pointed out. Results, obtained within this theoretical framework, are illustrated for the reaction Ca-40 (O-18, Ne-18)Ar-40 at 15.3 AMeV and compared to the data measured at INFN-LNS by the NUMEN Collaboration. Furthermore, preliminary results for reactions involving heavier systems, such as Se-76 (O-18, Ne-18)Ge-76, are shown.