E-viri
PDF
Recenzirano
Odprti dostop
-
Gando, A.; Gando, Y.; Hachiya, T.; Ha Minh, M.; 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, B. E.; Fujikawa, B. K.; Learned, J. G.; Maricic, J.; Winslow, L. A.; Efremenko, Y.; Karwowski, H. J.; Markoff, D. M.; Tornow, W.; O’Donnell, T.; Detwiler, J. A.; Enomoto, S.; Decowski, M. P.; Menéndez, J.; Dvornický, R.; Šimkovic, F.
Physical review letters, 05/2019, Letnik: 122, Številka: 19Journal Article
In this paper, we present a precision measurement of the $^{136}$Xe two-neutrino $\beta\beta$ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino $\beta\beta$ rate allows us to measure the ratio of the leading and subleading $2\nu\beta\beta$ nuclear matrix elements (NMEs), $\xi^{2\nu}_{31} = -0.26^{+0.31}_{-0.25}$. 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 $\xi^{2\nu}_{31}$ range allowed by the QRPA is excluded by the present measurement at the 90%25 C.L. Our analysis reveals that predicted $\xi^{2\nu}_{31}$ values are sensitive to the quenching of NMEs and the competing contributions from low- and high-energy states in the intermediate nucleus. Since these aspects are also at play in neutrinoless $\beta\beta$ decay, $\xi^{2\nu}_{31}$ provides new insights towards reliable neutrinoless $\beta\beta$ NMEs.
