Precision Analysis of the Xe 136 Two-Neutrino ββ Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements

(KamLAND-Zen Collaboration)

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10 Citations (Scopus)

Abstract

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.

Original languageEnglish
Article number192501
JournalPhysical review letters
Volume122
Issue number19
DOIs
Publication statusPublished - 2019 May 13

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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