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Double beta decay is so rare that parent isotopes are often described as "stable," and half lives run around 1020 years. Two-neutrino double beta decay has been observed. Neutrinoless double beta decay (0νββ) has not yet been observed conclusively. Such an observation would be groundbreaking and exciting, because the existence of this type of decay would tell physicists much about the nature of the neutrino.
The half life for 0νββ decay depends on matrix elements that can only be calculated in theory. However, the calculation of such matrix elements can be constrained by data obtained via charge-exchange experiments on targets made of the initial and final nuclei involved in 0νββ decay. In such experiments, excited states in the intermediate nucleus (Z+1) are populated. We have planned two charge-exchange experiments to measure such transitions: a (t,3He) experiment on the Z+2 nucleus at the NSCL and a (3He,t) experiment on the Z nucleus at RCNP. Each reaction will produce excited states in the Z+1 nucleus, and the results should provide a comprehensive picture of the transition strengths and allow us to constrain the calculations of 0νββ matrix elements.