Dark Matter Search Experiment with 20 kg xenon detector

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We reconsidered a shape of the detector in order to improve photon collection efficiency. We had a conclusion of a little bit smaller shape of a 15 kg detector had the best performance from the results of precise Monte Carlo simulation. The inner part of the chamber was modified to 15 kg from this decision. Radio activities of materials surrounding the detector and the detector itself were measured by a high purity germanium detector. These results were used to Monte Carlo simulation to understand the influence of background from each element. As a result, it was found out that the most influential material for the origin of gamma ray background was photo multiplier tubes. Then we need more effort to reduce radio activities from the photo multiplier tube. The precise measurements for neutron background were also made by a 3-He detector and a liquid scintillator. The results were one order higher than the expected event rate of dark matter. A distillation system was built to avoid the beta decay background from 85-krypton which are contained in xenon. We succeeded to reduce the krypton contamination in liquid xenon by a factor of 1/1000. 136-Xe double beta decay experiment and p-p and 7-Be low energy solar neutrino experiment as well as dark matter experiment at the same time using a double phase xenon detector were proposed.