- 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.
© 2015 Elsevier B.V. A search for double-beta decays of 136Xe to excited states of 136Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 01+, 21+ and 22+ transitions of 0νββ decay were evaluated in an exposure of 89.5 kg⋅yr of 136Xe, 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 21+ state transitions of 0νββ and 2νββ decay were improved to T1/20ν(0+→21+)>2.6×1025 yr and T1/22ν(0+→21+)>4.6×1023 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 01+ state of 136Xe for 0νββ and 2νββ decay. They are T1/20ν(0+→01+)>2.4×1025 yr and T1/22ν(0+→01+)>8.3×1023 yr (90% C.L.). The transitions to the 22+ states are also evaluated for the first time to be T1/20ν(0+→22+)>2.6×1025 yr and T1/22ν(0+→22+)>9.0×1023 yr (90% C.L.). These results are compared to recent theoretical predictions.