Neutrinoless double beta decay to excited collective 0⁺ states

Abstract

The many recently performed experiments to study the two-neutrino double beta (2νββ) decay to the first excited 0⁺ final state encourage similar experiments to be done for the neutrinoless double beta (0νββ) decay. Based on the accumulated theoretical and experimental information on the 2νββ decays one could hope that the 0νββ decay to the excited 0⁺ state would be very efficient in restricting the parameter space of modern particle-physics theories. In this article the 0νββ decays of ⁷⁶Ge and ⁸²Se to excited collective 0⁺ states are studied within a realistic nuclear model. It is found that the lower limits for the half-lives of these decays are of the order of 10²⁷ yr making them less sensitive than the ground-state decays, and practically impossible to detect in the near future.