期刊
NATURE
卷 510, 期 7504, 页码 229-234出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/nature13432
关键词
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资金
- DOE
- NSF in the United States
- NSERC in Canada
- SNF in Switzerland
- NRF in Korea
- RFBR in Russia [12-02-12145]
- DFG Cluster of Excellence 'Universe' in Germany
- Office of Science of the US DOE [DE-AC02-05CH11231]
- Direct For Mathematical & Physical Scien
- Division Of Physics [1132428] Funding Source: National Science Foundation
- Division Of Physics
- Direct For Mathematical & Physical Scien [1205977, 1307362] Funding Source: National Science Foundation
Many extensions of the standard model of particle physics suggest that neutrinos should be Majorana-type fermions-that is, that neutrinos are their own anti-particles-but this assumption is difficult to confirm. Observation of neutrinoless double-beta decay (0 nu beta beta), a spontaneous transition that may occur in several candidate nuclei, would verify the Majorana nature of the neutrino and constrain the absolute scale of the neutrino mass spectrum. Recent searches carried out with Ge-76 (the GERDA experiment) and Xe-136 (the KamLAND-Zen and EXO (Enriched Xenon Observatory)-200 experiments) have established the lifetime of this decay to be longer than 10(25) years, corresponding to a limit on the neutrino mass of 0.2-0.4 electronvolts. Here we report new results from EXO-200 based on a large Xe-136 exposure that represents an almost fourfold increase from our earlier published data sets. We have improved the detector resolution and revised the data analysis. The half-life sensitivity we obtain is 1.9x10(25) years, an improvement by a factor of 2.7 on previous EXO-200 results. We find no statistically significant evidence for 0 nu beta beta decay and set a half-life limit of 1.1x10(25) years at the 90 per cent confidence level. The high sensitivity holds promise for further running of the EXO-200 detector and future 0 nu beta beta decay searches with an improved Xe-based experiment, nEXO.
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