Abstract
A systematic study of the radioactive background in materials used in Ge-detector fabrication was conducted prior to the construction of an ultralow-background, 135 prototype detector. The background from primordial radioactivities in the new system was lower by factors of between 1.5× and 2.5× when compared to commercial low-background detectors. Data were collected for 8089 h with the detector located 1438 m underground, resulting in improved lower limits for the half-lives for both two-neutrino and neutrinoless ββ decay of to the ground state of and for the neutrinoless ββ decay to the first excited state of . The results of four recent theoretical calculations are compared in detail and used to extract limits on 〈〉, the Majorana mass of , and on the amplitudes of the couplings of right-handed Majorana neutrinos. The best combination of the lowest background data from recent experiments results in a new limit ≳3× yr, corresponding to 〈〉<2.4 eV neglecting right-handed couplings or 2.8 eV including both right-handed neutrino couplings.
- Received 25 November 1985
DOI:https://doi.org/10.1103/PhysRevC.34.666
©1986 American Physical Society