Status of balloon production for KamLAND-Zen 800 kg phase

Abstract KamLAND-Zen is an experiment for neutrinoless double beta decay ( 0 ν 2 β ) search with 136 Xe, based on the large liquid scintillator detector KamLAND. KamLAND-Zen includes 16.5 m 3 xenon loaded liquid scintillator in a 3.16 m diameter nylon balloon (inner-balloon) with 25 μm wall thickness. KamLAND-Zen 400 (383 kg 136 Xe used) released a lower limit on the 0 ν 2 β half-life of 136 Xe. However, the sensitivity is limited by the contamination of radioactive backgrounds from the inner-balloon. Then, we planned KamLAND-Zen 800, upgrading the detector with a new inner-balloon of 3.84 m diameter with 800 kg 136 Xe and 31.4 m 3 liquid scintillator. We present the current status of KamLAND-Zen, the new mini-balloon construction and methods to avoid background contaminations. In addition, the development of a scintillating balloon for future upgrades in order to remove the radioactive decay chain daughter nuclei bismuth is also introduced.