Constraints on the Decay of $^{180m}$$\mathrm{Ta}

• Published in: Physical review letters Vol. 131; no. 15
• Main Authors: Arnquist, I. J., Avignone, F. T., Barabash, A. S., Barton, C. J., Bhimani, K. H., Blalock, E., Bos, B., Busch, M., Buuck, M., Caldwell, T. S., Christofferson, C. D., Chu, P. -H., Clark, M. L., Cuesta, C., Detwiler, J. A., Efremenko, Yu, Ejiri, H., Elliott, S. R., Giovanetti, G. K., Goett, J., Green, M. P., Gruszko, J., Guinn, I. S., Guiseppe, V. E., Haufe, C. R., Henning, R., Hervas Aguilar, D., Hoppe, E. W., Hostiuc, A., Kim, I., Kouzes, R. T., Lannen V., T. E., Li, A., López-Castaño, J. M., Massarczyk, R., Meijer, S. J., Meijer, W., Oli, T. K., Paudel, L. S., Pettus, W., Poon, A. W. P., Radford, D. C., Reine, A. L., Rielage, K., Rouyer, A., Ruof, N. W., Schaper, D. C., Schleich, S. J., Smith-Gandy, T. A., Tedeschi, D., Thompson, J. D., Varner, R. L., Vasilyev, S., Watkins, S. L., Wilkerson, J. F., Wiseman, C., Xu, W., Yu, C. -H., Alves, D. S. M., Hebenstiel, L., Ramani, H.
• Format: Journal Article
• Language: English
• Published: United States American Physical Society (APS) 11-10-2023
• Subjects: 150 ≤ A ≤ 189; alpha decay; beta decay; isomer decays; lifetimes & widths; nuclear astrophysics; nuclear decay; NUCLEAR PHYSICS AND RADIATION PHYSICS; nuclear structure & decays; nuclear transition rates; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; radiation detectors
• ISSN: 0031-9007

$^{180m}$$\mathrm{Ta}$ is a rare nuclear isomer whose decay has never been observed. Its remarkably long lifetime surpasses the half-lives of all other known $β$ and electron capture decays due to the large K-spin differences and small energy differences between the isomeric and lower-energy states. Detecting its decay presents a significant experimental challenge but could shed light on neutrino-induced nucleosynthesis mechanisms, the nature of dark matter, and K-spin violation. For this study, we repurposed the Majorana Demonstrator, an experimental search for the neutrinoless double-beta decay of $^{76}$$\mathrm{Ge}$ using an array of high-purity germanium detectors, to search for the decay of $^{180m}$$\mathrm{Ta}$. Here, more than 17 kg, the largest amount of tantalum metal ever used for such a search, was installed within the ultralow-background detector array. In this Letter, we present results from the first year of Ta data taking and provide an updated limit for the $^{180m}$$\mathrm{Ta}$ half-life on the different decay channels. In conclusion, with new limits up to $\mathrm{1.5 × 10^{19} yr}$, we improved existing limits by 1–2 orders of magnitude which are the most sensitive searches for a single $β$ and electron capture decay ever achieved. Over all channels, the decay can be excluded for $T_\frac{1}{2} < 0.29 × 10^{18}$$\mathrm{yr}$.