Search for Majorana Neutrinos with the Complete KamLAND-Zen Dataset

We present a search for neutrinoless double-beta (\(0\nu\beta\beta\)) decay of \(^{136}\)Xe using the full KamLAND-Zen 800 dataset with 745 kg of enriched xenon, corresponding to an exposure of \(2.097\) ton yr of \(^{136}\)Xe. 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 \(0\nu\beta\beta\) decay half-life of \(T_{1/2}^{0\nu} > 3.8 \times 10^{26}\) 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.