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Precision Analysis of the Xe 136 Two-Neutrino β β Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements
Name
PhysRevLett.122.192501.pdf
Description
Published version
Size
420.98 KB
Format
Adobe PDF
Checksum (MD5)
a2ac5b33fe1cd9805e1da760c74f08e8
Date Issued
2019
Journal
Physical Review Letters
Publisher
American Physical Society (APS)
Version
Final published version
Abstract
© 2019 authors. Published by the American Physical Society. We present a precision analysis of the Xe136 two-neutrino ββ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino ββ rate allows us to measure the ratio of the leading and subleading 2νββ nuclear matrix elements (NMEs), ζ312ν=-0.26-0.25+0.31. Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consistent with the experimental limit. However, part of the ζ312ν range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted ζ312ν values are sensitive to the quenching of NMEs and the competing contributions from low- and high-energy states in the intermediate nucleus. Because these aspects are also at play in neutrinoless ββ decay, ζ312ν provides new insights toward reliable neutrinoless ββ NMEs.
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Creative Commons Attribution 4.0 International license
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DOI of Published Version
10.1103/PHYSREVLETT.122.192501
