Collaboration, K-Z; Gando, A; Gando, Y; Hanakago, H; Ikeda, H; Inoue, K; Kato, R; Koga, M; Matsuda, S; Mitsui, T; Nakada, T; Nakamura, K; Obata, A; Oki, A; Ono, Y; Shimizu, I; Shirai, J; Suzuki, A; Takemoto, Y; Tamae, K; Ueshima, K; Watanabe, H; Xu, BD; Yamada, S; Yoshida, H; Kozlov, A; Yoshida, S; Banks, TI; Detwiler, JA; Freedman, SJ; Fujikawa, BK; Han, K; O'Donnell, T; Berger, BE; Efremenko, Y; Karwowski, HJ; Markoff, DM; Tornow, W; Enomoto, S; Decowski, MP, *Limits on Majoron-emitting double-beta decays of Xe-136 in the
KamLAND-Zen experiment*,
Phys.Rev.C, vol. 86
(May, 2012),
pp. 021601 [1205.6372v2], [doi] .
**Abstract:**

*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.*