Current Status and Future Prospects of KamLAND-Zen*

KamLAND-Zen is searching for neutrino-less double beta decay using Xe-136 dissolved in ultra-low radioactivity liquid scintillator. It has run with 380 kg of 90% enriched Xe-136 and is providing the most stringent upper limit on effective Majorana mass of neutrino, 61-165 meV. Major backgrounds are Bi-214 as a contaminant on the mini-balloon, C-10 from cosmic muon spallation, and energy resolution tail of two neutrino double beta decay. KamLAND-Zen is replacing the mini-balloon with double capacity and specially cleaned mini-balloon so that effective Xe-136 amount can be increased by more than factor 3. Because spallation backgrounds associate preceding muon signal, a sophisticated software selection can drastically reduce C-10 backgrounds. This new phase is called KamLAND-Zen 800 and is expected to start this year with target sensitivity of ~40 meV entering inverted mass hierarchy of neutrinos. It will allow us to verify some theoretical models. In order to cover the inverted hierarchy region, energy resolution must be improved to distinguish neutrino-less and two neutrino double beta decays. KamLAND2-Zen is going to employ high quantum efficiency PMTs with light concentrators, and high light yield liquid scintillator. Energy resolution can be improved by more than factor 2 and the sensitivity will be ~20 meV covering almost entire inverted hierarchy region. Current status of KamLAND-Zen 800 deployment and development of KamLAND2-Zen items will be reported together with future prospects of these projects.