Departmental Bulletin Paper ZICOS : New project for neutrinoless double beta decay experiment using zirconium complex in liquid scintillator

FUKUDA, Yoshiyuki  ,  Narengerile  ,  OBATA, Akira  ,  MORIYAMA, Shigetaka  ,  OGAWA, Izumi  ,  GUNJI, Takahiro  ,  TSUKADA, Satoru  ,  HAYAMI, Ryohei

 A liquid scintillator containing a zirconium β-keto ester complex has been developed for the Zirconium COmplex in liquid Scintillator (ZICOS) experiment which is new project of neutrinoless double beta decay search. We are aiming to develop a detector which has a good energy resolution (3.5% at 3.35 MeV), a large light yield (60% that of BC505) and a low background rate (0.1 counts/tonne・year) with several hundred kg of 96Zr isotope, so we have investigated the zirconium β-keto ester complexes such as tetrakis (isopropyl acetoacetato) zirconium and tetrakis (ethyl acetoacetato) zirconium, which have high solubility (over 30 wt.%)in anisole. We measured the performance of liquid scintillator containing these zirconium β-keto ester complexes, and obtained 48.7+-7.1% of the light yield of BC505 and the energy resolution of 4.1+-0.6% at 3.35 MeV assuming 40% photo coverage of the photomultiplier in the detector. This results reached our initial goal, so we estimated that ZICOS experiment should be sensitive to <mV> < 0.2 - 0.3 eV assuming gA = 1.25, gPP = 1.11 and QRPA model, if a radius of the balloon is 1.5 m and the balloon is filled with a liquidscintillator containing 10 wt.% concentration of a zirconium β-keto ester complex with an enriched 96Zr.

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