Searching for neutrino-less double beta decay of 136Xe with PandaX-II liquid xenon detector

We report the Neutrino-less Double Beta Decay (NLDBD) search results from PandaX-II dual-phase liquid xenon time projection chamber. The total live time used in this analysis is 403.1 days from June 2016 to August 2018. With NLDBD-optimized event selection criteria, we obtain a fiducial mass of 219 kg of natural xenon. The accumulated xenon exposure is 242 kg.yr, or equivalently 22.2 kg.yr of Xe-136 exposure. At the region around Xe-136 decay Q-value of 2458 keV, the energy resolution of PandaX-II is 4.2%. We find no evidence of NLDBD in PandaX-II and establish a lower limit for decay half-life of 2.1 x 10(23) yr at the 90% confidence level, which corresponds to an effective Majorana neutrino mass m(beta beta) < (1.4 - 3.7) eV. This is the first NLDBD result reported from a dual-phase xenon experiment.