Constraints on the Decay of ^{180m}Ta

Area of Science:

• Nuclear Physics
• Astroparticle Physics

Background:

• Tantalum-180m (180mTa) is a long-lived nuclear isomer whose decay has never been observed.
• Its exceptionally long half-life is attributed to large K-spin differences and small energy gaps between isomeric and lower states.
• Observing its decay could provide insights into neutrino-induced nucleosynthesis, dark matter, and K-spin violation.

Purpose of the Study:

• To search for the decay of the tantalum-180m (180mTa) nuclear isomer.
• To establish new, more sensitive limits on the half-life of 180mTa.
• To explore the potential of repurposed experimental setups for novel nuclear decay searches.

Main Methods:

• Repurposed the Majorana Demonstrator, initially designed for neutrinoless double-beta decay searches of Germanium-76.
• Utilized an array of high-purity germanium detectors within an ultralow-background environment.
• Installed over 17 kg of tantalum metal, the largest amount used in such a search, for data collection.

Main Results:

• Presented results from the first year of data acquisition for tantalum-180m.
• Established new half-life limits for 180mTa decay across various channels, reaching up to 1.5 x 10^19 years.
• Improved existing limits by 1-2 orders of magnitude, achieving the most sensitive searches for single beta and electron capture decays to date.

Conclusions:

• The study successfully set stringent new limits on the half-life of tantalum-180m.
• The decay of 180mTa can be excluded for half-lives below 0.29 x 10^18 years across all channels.
• Demonstrated the efficacy of repurposing sensitive low-background detectors for exploring rare nuclear phenomena.