ZICOS – Neutrinoless double beta decay experiment using Zr-96 with an organic liquid scintillator-

A liquid scintillator containing a tetrakis (isopropyl acetoacetate) zirconium has been developed for new project of neutrinoless 96 ^{96} Zr double beta decay experiment. The liquid scintillator has 1.4 wt.% concentration of Zr, light yield of 48±7.1 48 \pm 7.1 % for BC505, and an energy resolution of 2.5±0.4 2.5 \pm 0.4 % at 3.35 MeV assuming 64 % photo coverage. In order to investigate a half-life over 1026 10^{26} years, we need to remove backgrounds such as 208 ^{208} Tl over one order magnitude. For this purpose, we have developed new technique to use Cherenkov light using their characteristic photon hit pattern, and have obtained the efficieny that 93% of 208 ^{208} Tl backgrounds could be reduced even though remaining 80% of double beta decay signal. In order to use this technique, we have to separate Cherenkov and Scintillation lights emitted from a few MeV electron using the pulse shape discrimination. Here, we will report recent results of our measurement of pulse shape using the FADC digitizer.