Search for Majorana Neutrinos Near the Inverted Mass Hierarchy Region with KamLAND-Zen.
- Author(s): Gando, A;
- Gando, Y;
- Hachiya, T;
- Hayashi, A;
- Hayashida, S;
- Ikeda, H;
- Inoue, K;
- Ishidoshiro, K;
- Karino, Y;
- Koga, M;
- Matsuda, S;
- Mitsui, T;
- Nakamura, K;
- Obara, S;
- Oura, T;
- Ozaki, H;
- Shimizu, I;
- Shirahata, Y;
- Shirai, J;
- Suzuki, A;
- Takai, T;
- Tamae, K;
- Teraoka, Y;
- Ueshima, K;
- Watanabe, H;
- Kozlov, A;
- Takemoto, Y;
- Yoshida, S;
- Fushimi, K;
- Banks, TI;
- Berger, BE;
- Fujikawa, BK;
- O'Donnell, T;
- Winslow, LA;
- Efremenko, Y;
- Karwowski, HJ;
- Markoff, DM;
- Tornow, W;
- Detwiler, JA;
- Enomoto, S;
- Decowski, MP;
- KamLAND-Zen Collaboration
- et al.
Published Web Location
https://arxiv.org/pdf/1605.02889v2Abstract
We present an improved search for neutrinoless double-beta (0νββ) decay of ^{136}Xe in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a significant reduction of the ^{110m}Ag contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>1.07×10^{26} yr at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61-165 meV. For the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region.