1205.6372 (KamLAND-Zen Collaboration: A. Gando et al.)

Limits on Majoron-Emitting Double-Beta Decays of Xe-136 in KamLAND-Zen    [PDF]

KamLAND-Zen Collaboration: 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. Ueshima, H. 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

We present limits on Majoron-emitting neutrinoless double-beta decay modes based on an exposure of 112.3 days with 125 kg of Xe-136. In particular, a lower limit on the ordinary (spectral index n = 1) Majoron-emitting decay half-life of Xe-136 is obtained as T_{1/2}^{0\nu\chi^{0}} > 2.6 x 10^{24} 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 < (0.8 - 1.6) x 10^{-5}. This excludes a previously unconstrained region of parameter space and strongly limits the possible contribution of ordinary Majoron emission modes to 0\nu\beta\beta decay for neutrino masses in the inverted hierarchy scheme.

View original: http://arxiv.org/abs/1205.6372