Limits on Majoron-emitting double-β decays of 136Xe in the KamLAND-Zen experiment

A. Gando, Y. Gando, H. Hanakago, H. Ikeda, K. Inoue, R. Kato, M. Koga, S. Matsuda, T. Mitsui, T. Nakada, K. Nakamura, A. Obata, A. Oki, Y. Ono, I. Shimizu, J. Shirai, A. Suzuki, Y. Takemoto, K. Tamae, K. UeshimaH. Watanabe, B. D. Xu, S. Yamada, H. Yoshida, A. Kozlov, S. Yoshida, T. I. Banks, J. A. Detwiler, S. J. Freedman, B. K. Fujikawa, K. Han, T. O'Donnell, B. E. Berger, Y. Efremenko, H. J. Karwowski, D. M. Markoff, W. Tornow, S. Enomoto, M. P. Decowski

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We present limits on Majoron-emitting neutrinoless double-β decay modes based on an exposure of 112.3 days with 125 kg of 136Xe. In particular, a lower limit on the ordinary (spectral index n=1) Majoron-emitting decay half-life of 136Xe is obtained as T1/20νχ0>2.6×1024 yr at 90% C.L., a factor of five more stringent than previous limits. The corresponding upper limit on the effective Majoron-neutrino coupling, using a range of available nuclear matrix calculations, is gee<(0.8-1.6) ×10-5. This excludes a previously unconstrained region of parameter space and strongly limits the possible contribution of ordinary Majoron emission modes to 0νββ decay for neutrino masses in the inverted hierarchy scheme.

Original languageEnglish
Article number021601
JournalPhysical Review C - Nuclear Physics
Issue number2
Publication statusPublished - 2012 Aug 6


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