Abstract
Ta180m 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 Ge76 using an array of high-purity germanium detectors, to search for the decay of Ta180m. 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 Ta180m half-life on the different decay channels. With new limits up to 1.5×1019 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 T1/2<0.29×1018 yr.
| Original language | English |
|---|---|
| Article number | 152501 |
| Journal | Physical Review Letters |
| Volume | 131 |
| Issue number | 15 |
| DOIs | |
| State | Published - Oct 13 2023 |
Funding
We gratefully acknowledge that the research presented in this report was supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory under Project No. 20220092ER, which enabled the rare decay search. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contracts or Grants No. DE-AC02-05CH11231, No. DE-AC05-00OR22725, No. DE-AC05-76RL0130, No. DE-FG02-97ER41020, No. DE-FG02-97ER41033, No. DE-FG02-97ER41041, No. DE-SC0012612, No. DE-SC0014445, No. DE-SC0018060, No. DE-SC0022339, and No. LANLEM77/LANLEM78. We acknowledge support from the Particle Astrophysics Program and Nuclear Physics Program of the National Science Foundation through Grants No. MRI-0923142, No. PHY-1003399, No. PHY-1102292, No. PHY-1206314, No. PHY-1614611, No. PHY-1812409, No. PHY-1812356, No. PHY-2111140, and No. PHY-2209530. We gratefully acknowledge the support of the Laboratory Directed Research and Development (LDRD) program at Lawrence Berkeley National Laboratory for this work. We gratefully acknowledge the support of the U.S. Department of Energy through the Los Alamos National Laboratory LDRD Program, the Oak Ridge National Laboratory LDRD Program, and the Pacific Northwest National Laboratory LDRD Program for this work. We gratefully acknowledge the support of the South Dakota Board of Regents Competitive Research Grant. We acknowledge the support of the Natural Sciences and Engineering Research Council of Canada, funding Reference No. SAPIN-2017-00023, and from the Canada Foundation for Innovation John R. Evans Leaders Fund. We acknowledge support from the 2020/2021 L’Oréal-UNESCO for Women in Science Program. This research used resources provided by the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory and by the National Energy Research Scientific Computing Center, a U.S. Department of Energy Office of Science User Facility. We thank our hosts and colleagues at the Sanford Underground Research Facility for their support.
| Funders | Funder number |
|---|---|
| Canada Foundation for Innovation John R. Evans Leaders Fund | |
| National Science Foundation | PHY-1003399, PHY-1812409, PHY-1206314, PHY-1614611, PHY-1102292, PHY-2209530, PHY-1812356, MRI-0923142, PHY-2111140 |
| U.S. Department of Energy | |
| Office of Science | |
| Nuclear Physics | DE-AC05-00OR22725, DE-AC05-76RL0130, DE-AC02-05CH11231, DE-SC0012612, DE-FG02-97ER41020, DE-FG02-97ER41033, DE-SC0022339, LANLEM77/LANLEM78, DE-FG02-97ER41041, DE-SC0018060, DE-SC0014445 |
| Oak Ridge National Laboratory | |
| Laboratory Directed Research and Development | |
| South Dakota Board of Regents | |
| Los Alamos National Laboratory | 20220092ER |
| Pacific Northwest National Laboratory | |
| National Energy Research Scientific Computing Center | |
| Natural Sciences and Engineering Research Council of Canada | SAPIN-2017-00023 |