Precision Analysis of the Xe136 Two-Neutrino ββ Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements

Autor: A. Gando, T. O'Donnell, Y. Kamei, Sanshiro Enomoto, S. Hirata, S. Hayashida, Yu. Efremenko, K. Soma, M Ha Minh, S. Umehara, Hugon J Karwowski, Fedor Šimkovic, Hideki Watanabe, Y. Gando, K. Tamae, John G. Learned, S. Matsuda, B. K. Fujikawa, B. E. Berger, K. Ueshima, S. Otsuka, J. A. Detwiler, Lindley Winslow, S. Obara, D. M. Markoff, K. Hosokawa, Akira Ono, J. Maricic, H. Ozaki, N. Ota, Toyohiko Kinoshita, D. Chernyak, M. P. Decowski, Y. Honda, Ken-Ichi Fushimi, A. Suzuki, T. Mitsui, T. Hachiya, K. Nakamura, A. Kozlov, Koji Ishidoshiro, Werner Tornow, K. Kamizawa, Y Takemoto, Kunio Inoue, I. Shimizu, R Dvornický, Tsugio Sato, S. Yoshida, H. Ikeda, Y. Shibukawa, A. Takeuchi, J. Shirai, Y. Shirahata, M. Koga, Javier Fernandez Menendez
Rok vydání: 2019
Předmět:
Zdroj: Physical Review Letters. 122
ISSN: 1079-7114
0031-9007
Popis: We present a precision analysis of the ^{136}Xe 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), ξ_{31}^{2ν}=-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 ξ_{31}^{2ν} range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted ξ_{31}^{2ν} 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, ξ_{31}^{2ν} provides new insights toward reliable neutrinoless ββ NMEs.
Databáze: OpenAIRE
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