1. Precision Analysis of the Xe136 Two-Neutrino ββ Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements
- Author
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Gando, A, Gando, Y, Hachiya, T, Minh, M Ha, Hayashida, S, Honda, Y, Hosokawa, K, Ikeda, H, Inoue, K, Ishidoshiro, K, Kamei, Y, Kamizawa, K, Kinoshita, T, Koga, M, Matsuda, S, Mitsui, T, Nakamura, K, Ono, A, Ota, N, Otsuka, S, Ozaki, H, Shibukawa, Y, Shimizu, I, Shirahata, Y, Shirai, J, Sato, T, Soma, K, Suzuki, A, Takeuchi, A, Tamae, K, Ueshima, K, Watanabe, H, Chernyak, D, Kozlov, A, Obara, S, Yoshida, S, Takemoto, Y, Umehara, S, Fushimi, K, Hirata, S, Berger, BE, Fujikawa, BK, Learned, JG, Maricic, J, Winslow, LA, Efremenko, Y, Karwowski, HJ, Markoff, DM, Tornow, W, O’Donnell, T, Detwiler, JA, Enomoto, S, Decowski, MP, Menéndez, J, Dvornický, R, and Šimkovic, F
- Subjects
Nuclear and Plasma Physics ,Particle and High Energy Physics ,Synchrotrons and Accelerators ,Physical Sciences ,KamLAND-Zen Collaboration ,hep-ex ,nucl-ex ,nucl-th ,Mathematical Sciences ,Engineering ,General Physics ,Mathematical sciences ,Physical sciences - Abstract
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.
- Published
- 2019