Spin dipole nuclear matrix elements for double beta decay nuclei by charge-exchange reactions

Spin dipole (SD) strengths for double beta-decay (DBD) nuclei were studied experimentally for the first time by using measured cross sections of (³He, t) charge-exchange reactions (CERs). Then SD nuclear matrix elements (NMEs) $M_{\alpha }\left(SD\right)$ for low-lying 2⁻ states were derived from the experimental SD strengths by referring to the experimental α = GT (Gamow–Teller) and α = F (Fermi) strengths. They are consistent with the empirical NMEs $M\left(SD\right)$ based on the quasi-particle model with the empirical effective SD coupling constant. The CERs are used to evaluate the SD NME, which is associated with one of the major components of the neutrino-less DBD NME. (letter)