Exploring the Isomeric Decay of ^180mTa with the MAJORANA DEMONSTRATOR: New Insights from the Second Year of Data

The MAJORANA DEMONSTRATOR experiment, known for its ultra-low-background capabilities, has adapted its apparatus to investigate the rare decay of a unique isotope. Uniquely, ^180mTa is the only known naturally occurring isotope that exists in an isomeric state rather than a ground state. This elusive isomeric decay is hindered by spin suppression. Measuring its decay rate can provide valuable insights into its production mechanisms, such as neutrino-induced reactions. Beyond probing a nuclear decay on the extreme scale, measuring the decay rate also offers the potential to probe dark matter through stimulated decay, complementing the efforts of large-scale detectors.

To achieve this, we placed Ta samples among the Ge detectors, leveraging the deep-underground ultra-low background environment, the exceptional resolution of the MAJORANA detectors, and established analytical methods to search for both the nuclear decay and potential dark matter-induced emissions. While the first year of data collection faced backgrounds from surface activation but still managed to set world-leading limits. In this presentation, I will share findings from our latest data collection and analysis improvements, including new results from the second year of data taking.