The MAJORANA DEMONSTRATOR is searching for double-beta decay of $^{ 76}$Ge to excited states (E.S.) in $^{ 76}$Se using a modular array of high purity Germanium detectors. $^{ 76}$Ge can decay into three E.S.s of $^{ 76}$Se. The E.S. decays have a clear event signature consisting of a $\beta\beta$-decay with the prompt emission of one or two $\gamma$-rays, resulting in with high probability in a multi-site event. The granularity of the DEMONSTRATOR detector array enables powerful discrimination of this event signature from backgrounds. Using 21.3 kg-y of isotopic exposure, the DEMONSTRATOR has set world leading limits for each E.S. decay, with 90% CL lower half-life limits in the range of $(0.56-2.1)\cdot10^{ 24}$ y. In particular, for the $2\nu$ transition to the first $0^+$ E.S. of $^{ 76}$Se, a lower half-life limit of $0.68\cdot10^{ 24}$ at 90% CL was achieved.
Categories: nucl-ex