New developments in modeling Heavy Ion Double Charge Exchange reactions

Heavy Ion Double Charge Exchange (HIDCE) nuclear reactions are described in terms of sequential meson-exchange, i.e., as a sequence of two independent single charge exchange reactions (Double Single Charge Exchange, DSCE). HIDCE reactions may represent a powerful tool to get information on the Nuclear Matrix Element (NME) describing double beta decays, thanks to the analogies found between the structures of DSCE nuclear response tensors and the nuclear matrix elements of double beta decays. Heavy Ion DSCE reactions are treated within second order DWBA framework; this allows to express DSCE reaction amplitude as a superposition of distortion factors, accounting for initial and final state ion-ion elastic interactions, and nuclear matrix elements. Explicit expressions for the latter are derived using QRPA theory. Reduction schemes for treating DSCE transition form factors are discussed, allowing to get disentangled projectile and target NMEs within DSCE cross section expression. Calculations are performed for some of the reactions studied within the NUMEN collaboration, such as 40Ca (18O, 18Ne) 40Ar, 76Se (18O, 18Ne) 76Ge and 76Ge(20Ne,20O)76Se, at a beam energy of 15.3 AMeV.