Electro-magnetic transitions from isobaric analogue states to study nuclear matrix elements for double beta decays

Nuclear matrix element (NME M0ν) for neutrinoless double beta decay (DBD) of XZA→XZ+2A with A and Z being the mass and atomic numbers is shown for the first time to be experimentally studied by measuring electromagnetic transition rates from the isobaric analogue state (IAS) of XZA to low-lying states in the intermediate nucleus of XZ+1A. NMEs for electric dipole and magnetic dipole transitions from IAS are used to evaluate vector dipole and Gamow-Teller NMEs associated with DBD and the effective weak couplings to help theoretical model calculations of the DBD NME. The IAS gamma transition rates and the cross sections are evaluated for DBD nuclei to show that the IAS gamma experiments are quite feasible and realistic.