- Asakura, K
- Gando, A
- Gando, Y
- Hachiya, T
- Hayashida, S
- Ikeda, H
- Inoue, K
- Ishidoshiro, K
- Ishikawa, T
- Ishio, S
- Koga, M
- Matsuda, S
- Mitsui, T
- Motoki, D
- Nakamura, K
- Obara, S
- Otani, M
- Oura, T
- Shimizu, I
- Shirahata, Y
- Shirai, J
- Suzuki, A
- Tachibana, H
- Tamae, K
- Ueshima, K
- Watanabe, H
- Xu, BD
- Yoshida, 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.
A search for double-beta decays of Xe to excited states of Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 0 , 2 and 2 transitions of 0νββ decay were evaluated in an exposure of 89.5 kg⋅yr of Xe, while the same transitions of 2νββ decay were evaluated in an exposure of 61.8 kg⋅yr. No excess over background was found for all decay modes. The lower half-life limits of the 2 state transitions of 0νββ and 2νββ decay were improved to T1/20ν(0 →2 )>2.6×10 yr and T (0 →2 )>4.6×10 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 0 state of Xe for 0νββ and 2νββ decay. They are T (0 →0 )>2.4×1025 yr and T (0 →0 )>8.3×1023 yr (90% C.L.). The transitions to the 2 states are also evaluated for the first time to be T (0 →2 )>2.6×10 yr and T (0 →2 )>9.0×10 yr (90% C.L.). These results are compared to recent theoretical predictions. 136 136 + + + 136 + + + 25 2ν + + 23 + 136 0ν + + 2ν + + + 0ν + + 25 2ν + + 23 1 1 2 1 1 1/2 1 1 1/2 1 1/2 1 2 1/2 2 1/2 2