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
- et al.
Published Web Location
https://arxiv.org/pdf/1605.02889v2Abstract
© 2016 American Physical Society. We present an improved search for neutrinoless double-beta (0νββ) decay of Xe136 in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a significant reduction of the Ag110m 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 T1/20ν>1.07×1026 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.