The MAJORANA DEMONSTRATOR's Search for Double-Beta Decay of ⁷⁶Ge to Excited States of ⁷⁶Se

The MAJORANA DEMONSTRATOR concluded its search for neutrinoless double-beta decay in 2021. The experiment operated an array of up to 40.4 kg of germanium detectors, 29.7 kg of which were isotopically enriched in ⁷⁶Ge. Thanks to its ultra-low backgrounds, excellent energy resolution, and background rejection capabilities, the DEMONSTRATOR was able to execute a broad program of searches for other rare physical processes. One such process is the double-beta decay of ⁷⁶Ge into excited states of ⁷⁶Se, which has not been observed before. Six possible decay modes exist, each of which produce events spanning multiple detectors that can be separated from backgrounds. The DEMONSTRATOR previously set world-leading limits in the range of (0.75-4.0)×10²⁴ y (90% C.I.) on the various decay modes of ⁷⁶Ge with 41.9 kg-y of isotopic exposure. With its full dataset, the DEMONSTRATOR has collected 97.7 kg-y of isotopic exposure (defined to include all ⁷⁶Ge mass in the detector array, including inactive mass), of which 60.8 kg-y is blinded. In addition, we implemented improved analysis techniques that take advantage of the multi-site event discriminator and updated background model to further improve sensitivity. This talk will present an updated search for double-beta decay of ⁷⁶Ge to excited states of ⁷⁶Se, and will highlight searches for physics beyond the Standard Model that were conducted by the MAJORANA DEMONSTRATOR.