https://doi.org/10.1140/epjc/s10052-023-11516-9
Regular Article - Experimental Physics
New limit on 
Zr double beta decay to the 1st excited state of Mo
1
Gran Sasso Science Institute, 67100, L’Aquila, Italy
2
INFN-Laboratori Nazionali del Gran Sasso, 67100, Assergi, L’Aquila, Italy
3
Faculty of Mathematics, Physics and Informatics, Comenius University, 84248, Bratislava, Slovakia
4
Department of Physics, Engineering Physics and Astronomy, Queen’s University, K7L 3N6, Kingston, ON, Canada
5
Arthur B. McDonald Canadian Astroparticle Physics Research Institute, K7L 3N6, Kingston, ON, Canada
6
Department of Chemistry, Queen’s University, K7L 3N6, Kingston, ON, Canada
Received:
1
February
2023
Accepted:
17
April
2023
Published online:
11
May
2023
A new study of double beta decay processes in natural Zr isotopes using Zr metal samples and an ultra-low-background high-purity germanium detectors was performed at Laboratori Nazionali del Gran Sasso of INFN (Italy). Two data sets were collected with a 736.35 g and a 129.94 g Zr metal over 59.7 days and 37.3 days, respectively, and were used for a detailed analysis. A new limit on the double beta decay of Zr to the 1st excited level of Mo was set as 
, which is a factor of three better than the previous result. It is shown that the current radiopurity of Zr metal (tens of Bq/kg), produced via two methods, do not comply with the radiopurity requirements for low-background experiments. Hence, we propose to use a purified ZrCl
powder in an optimized geometry as a new approach for future experiments with extended sensitivity focused on studies of rare nuclear processes in Zr isotopes.
© The Author(s) 2023
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