Search for galactic dark matter and double beta decay measurement using a detector of new principle

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A dedicated dilution refrigerator has been constructed. It is capable of cooling the detector material down to 10mK.It is made of specially selected raw materials to reduce natural radiation background from them.In order to manufacture thermistors with high sensitivities at low temperature, neutron transmutation doping method was adopted.Neutron irradiation has been done at the JRR-3 reactor of the Japan Atomic Energy Reasearch Institute.Using these building elements, we developed cryogenic particle detectors consisting of 8 pieces of 20-gram lithium fluoride bolometers. The lithium fluoride is known to be the material which has the largest cross section for the detection of spin dependently interacting supersymmetric neutralinos. With these detectors a direct experimental search for supersymmetric particle dark matter has been performed and is still ongoing in the Nokogiri-yama underground cell of the institute for the Cosmic Ray Research, University of Tokyo.On the basis of a pilot run, limits were obtained on normalized point-like cross section for the spin-dependently interacting neutralino incident on a single proton, although the dark matter is not yet deiscovered.While the shielding against back-ground radiation is not fully optimized yet, our search gave the worls best limits for the spin-dependently interacting neutralino with a mass lower than 5 GeV.It demonstrates the advantages of using the fluorine for the target and the low energy threshold of the bolometer. Thwe search continues with the improved shielding and more efficient veto counters.