Recent results from KamLAND-Zen

Abstract

A search for the neutrinoless double beta decay of $^{136}$Xe was conducted with the xenon-loaded liquid scintillator detector KamLAND-Zen 800 using 970 kg$\cdot$year of $^{136}$Xe exposure. No significant signal excess from the expected background was observed from the energy spectrum fitting, and we set a lower limit on the half-life of 2.0 $\times$ 10$^{26}$ years at a 90% confidence level. A combined fit of the KamLAND-Zen 400 and 800 data sets gives a lower limit of the half-life of 2.3 $\times$ 10$^{26}$ years at a 90% confidence level. It corresponds to the upper limits on the effective Majorana neutrino mass of 36 - 156 meV with various nuclear matrix element calculations. It is the first test for inverted mass ordering.