Search For Double-Beta Decay Of Ge-76 To Excited States Of Se-76 With The Majorana Demonstrator

The MAJORANA DEMONSTRATOR is a neutrinoless double-beta decay search consisting of a low-background modular array of high-purity germanium detectors, similar to 2/3 of which are enriched to 88% in Ge-76. The experiment is also searching for double-beta decay of Ge-76 to excited states (e.s.) in Se-76. Ge-76 can decay into three daughter states of Se-76, with clear event signatures consisting of a beta beta-decay followed by the prompt emission of one or two. rays. This results with high probability in multi-detector coincidences. The granularity of the DEMONSTRATOR detector array enables powerful discrimination of this event signature from backgrounds. Using 41.9 kg yr of isotopic exposure, the DEMONSTRATOR has set world leading limits for each e.s. decay of Ge-76, with 90% CL lower half-life limits in the range of (0.75-4.0) x 10(24) yr. In particular, for the 2 nu transition to the first 0(+) e.s. of Se-76, a lower half-life limit of 7.5 x 10(23) yr at 90% CL was achieved.