Dark matter search at the Kamioka mine
The direct experimental search for supersymmetric particle dark matter is running in a newly caved underground cell in the Kamioka Observatory. The detector consists of 8 pieces of 20-gram lithium fluoride bolometers, and has an inside shield with very old lead which contains very little radioactivities. The fluorine is estimated to be one of the best nuclides for the detection of spin-dependently interacting neutralinos. The measurement started in the year 2000 and has accumulated data for the search as well as for the study of environmental radioactivity background.
Solar axion search experiment
We are also running an experiment to search for axions, light neutral pseudoscalar particles yet to be discovered. Its existence is implied to solve the so-called strong CP problem. The axion would be produced in the solar core through the Primakoff effect if its mass is a few electronvolts. It can be converted back to an x-ray in a strong magnetic field in the laboratory by the inverse process. We search for such x-rays coming from the direction of the sun with the AXION HELIOSCOPE. The axion helioscope consists of a cryogen-free 4T superconducting magnet with an effective length of 2300 mm and PIN photodiodes as x-ray detectors. It is mounted on a computer-controlled altazimuth to track the sun. In the search experiments we got upper limits to the coupling constant of axions to photons in ma region less than 0.26eV. The AXION HELIOSCOPE has also been used to search for possible axions emitted by other celestial objects. We scanned about 10% of the celestial sphere and searched for point axion sources. We also searched for axions from four compact objects, the galactic center, Sco X-1, Vela X-1, and Crab nebula. No positive signal is observed in either searches by now.
