1. Kamioka Observatory, Institute for Cosmic Ray Research, the University of Tokyo, Higashi-Mozumi, Kamioka, Hida, Gifu 506-1205, Japan
2. Kavli Institute for the Physics and Mathematics of the Universe (WPI), the University of Tokyo, Kashiwa, Chiba 277-8582, Japan
3. Center of Underground Physics, Institute for Basic Science, 70 Yuseong-daero 1689-gil, Yuseong-gu, Daejeon 305-811, South Korea
4. Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Aichi 464-8601, Japan
5. Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
6. Institute of Socio-Arts and Sciences, The University of Tokushima, 1-1 Minamijosanjimacho Tokushima city, Tokushima 770-8502, Japan
7. Department of Physics, Kobe University, Kobe, Hyogo 657-8501, Japan
8. Korea Research Institute of Standards and Science, Daejeon 305-340, South Korea
9. Department of Physics, Miyagi University of Education, Sendai, Miyagi 980-0845, Japan
10. Department of Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan
11. Department of Physics, Faculty of Engineering, Yokohama National University, Yokohama, Kanagawa 240-8501, Japan