Investigation of the decay of to excited states in

The two-neutrino mode of double beta decay ($2νββ$) of ⁹⁶Zr is investigated both theoretically and experimentally. The calculations, using the quasiparticle random phase approximation approach, show that for ⁹⁶Zr the detection of 2νββ transitions to the two first excited states in the daughter nuclide will be possible in the very near future. On the experimental side, new, most stringent limits on half-lives for the double beta decay of ⁹⁶Zr to excited states in ⁹⁶Mo have been obtained with a 430 cm³ ‘well-type’ germanium detector. They range between 5 × 10¹⁹ and 8 × 10¹⁹ years (90% CL)