Overview of the New KamLAND-Zen 800 Bayesian Analysis

The KamLAND Zero-Neutrino Double-Beta Decay Experiment (KamLAND-Zen or KLZ-800) located near Kamioka, Japan, uses about 800 kg of enriched Xenon (~91 percent Xe-136 and ~9 percent Xe-134) to search for neutrinoless double beta decay at the energy region of interest (ROI) around 2.458 MeV. It currently provides the most stringent limit on the Majorana neutrino mass by performing a multivariate spectral fit in the energy range between 0.5 to 4.8 MeV to obtain the background levels in the ROI with highest possible precision. In this talk, the new and recently published results for a full Bayesian approach will be discussed. An emphasis will be put on the statistical framework and the treatment of systematics. For the entire KLZ-800 only dataset with an exposure of 2.097 ton × years and without addressing the combination with the previous KLZ-400 phase, an evidence for a signal has been rejected leading to a lower half-life limit of 3.4 × 10²⁶ years at 90 percent credibility level. This talk is presented on behalf of the KamLAND-Zen Collaboration.