Status of balloon production for KamLAND-Zen 800 kg phase

摘要

KamLAND-Zen is an experiment for neutrinoless double beta decay (Ov2β) 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 Ov2β 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.