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Search for double-beta decay of 136Xe to excited states of 136Ba with the KamLAND-Zen experiment

  • Author(s): 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.
Abstract

© 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.

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