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Title: Search for Majorana Neutrinos Near the Inverted Mass Hierarchy Region with KamLAND-Zen

Here, we present an improved search for neutrinoless double-beta (0νββ) decay of Xe 136 in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a significant reduction of the Ag 110m contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the 0νββ decay half-life of T$$0v\atop{1/2}$$ > 1.07×10 26 yr at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61-165 meV. Finally, for the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region.
Authors:
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Publication Date:
OSTI Identifier:
1379566
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 117; Journal Issue: 8; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Contributing Orgs:
KamLAND-Zen Collaboration
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS