Search for Majorana Neutrinos with the Complete KamLAND-Zen Dataset

We present a search for neutrinoless double-beta (0) decay of ^136Xe using the full KamLAND-Zen 800 dataset with 745 kg of enriched xenon, corresponding to an exposure of 2. 097 ton yr of ^136Xe. This updated search benefits from a more than twofold increase in exposure, recovery of photo-sensor gain, and reduced background from muon-induced spallation of xenon. Combining with the search in the previous KamLAND-Zen phase, we obtain a lower limit for the 0 decay half-life of T₁/₂^0 > 3. 8 10^26 yr at 90% C. L. , a factor of 1. 7 improvement over the previous limit. The corresponding upper limits on the effective Majorana neutrino mass are in the range 28-122 meV using phenomenological nuclear matrix element calculations.