Published October 11, 2023
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Constraints on the Decay of ^{180m}Ta.

Creators

  • 1. Pacific Northwest National Laboratory, Richland, Washington 99354, USA
  • 2. Pacific Northwest National Laboratory
  • 3. Department of Physics and Astronomy, University of South Carolina, Columbia, South Carolina 29208, USA
  • 4. University of South Carolina
  • 5. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
  • 6. Oak Ridge National Laboratory
  • 7. National Research Center "Kurchatov Institute," Kurchatov Complex of Theoretical and Experimental Physics, Moscow 117218, Russia
  • 8. Kurchatov Institute
  • 9. Department of Physics, University of South Dakota, Vermillion, South Dakota 57069, USA
  • 10. Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27514, USA
  • 11. Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA
  • 12. Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA
  • 13. North Carolina State University
  • 14. Department of Physics, Duke University, Durham, North Carolina 27708, USA
  • 15. Duke University
  • 16. Center for Experimental Nuclear Physics and Astrophysics, and Department of Physics, University of Washington, Seattle, Washington 98195, USA
  • 17. University of Washington
  • 18. South Dakota Mines, Rapid City, South Dakota 57701, USA
  • 19. Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  • 20. Los Alamos National Laboratory
  • 21. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, CIEMAT 28040, Madrid, Spain
  • 22. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37916, USA
  • 23. University of Tennessee
  • 24. Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
  • 25. Osaka University
  • 26. Physics Department, Williams College, Williamstown, Massachusetts 01267, USA
  • 27. IU Center for Exploration of Energy and Matter, and Department of Physics, Indiana University, Bloomington, Indiana 47405, USA
  • 28. Indiana University
  • 29. Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
  • 30. Lawrence Berkeley National Laboratory
  • 31. Joint Institute for Nuclear Research, Dubna 141980, Russia
  • 32. Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
  • 33. IU Center for Exploration of Energy and Matter, and Department of Physics, Indiana University, Bloomington, Indiana 47405, USA.
  • 34. Stanford Institute for Theoretical Physics, Stanford University, Stanford, California 94305, USA.
  • 35. Stanford University

Description

^{180m}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}Ge using an array of high-purity germanium detectors, to search for the decay of ^{180m}Ta. 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}Ta half-life on the different decay channels. With new limits up to 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_{1/2}<0.29×10^{18}  yr.
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