Limit on Neutrinoless ββ Decay of 136Xe from the First Phase of KamLAND-Zen and Comparison with the Positive Claim in 76Ge

We present results from the first phase of the KamLAND-Zen double-beta decay experiment, corresponding to an exposure of 89.5 kg yr of Xe-136. We obtain a lower limit for the neutrinoless double-beta decay half-life of T(1/2)0(v) > 1.9 x 10(25) yr at 90% C.L. The combined results from KamLAND-Zen and EXO-200 give T(1/2)0(v) > 3.4 x 10(25) yr at 90% C.L., which corresponds to a Majorana neutrino mass limit of < m(beta beta)> < (120- 250) meV based on a representative range of available matrix element calculations. Using those calculations, this result excludes the Majorana neutrino mass range expected from the neutrinoless double-beta decay detection claim in Ge-76, reported by a part of the Heidelberg-Moscow Collaboration, at more than 97.5% C.L. DOI: 10.1103/PhysRevLett.110.062502