Affiliation: | a Department of Physics, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan b International Center for Elementary Particle Physics, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan c Cryogenic Center, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113, Japan |