[1] Univ Utah, High Energy Astrophys Inst, Salt Lake City, UT 84112 USA
[2] Univ Yamanashi, Interdisciplinary Grad Sch Med & Engn, Kofu, Yamanashi, Japan
[3] Tokyo Inst Technol, Meguro Ku, Tokyo 152, Japan
[4] Hanyang Univ, Seoul 133791, South Korea
[5] Tokyo Univ Sci, Noda, Chiba 278, Japan
[6] Kinki Univ, Higashiosaka, Osaka 577, Japan
[7] Yonsei Univ, Seoul 120749, South Korea
[8] Natl Lab High Energy Phys, KEK, Inst Particle & Nucl Studies, Tsukuba, Ibaraki 305, Japan
[9] Osaka City Univ, Osaka 558, Japan
[10] Univ Tokyo, Inst Cosm Ray Res, Kashiwa, Chiba, Japan
[11] Russian Acad Sci, Inst Nucl Res, Moscow 117312, Russia
[12] Kanagawa Univ, Yokohama, Kanagawa, Japan
[13] Saitama Univ, Saitama 3388570, Japan
[14] Rutgers State Univ, Piscataway, NJ USA
[15] Tokyo City Univ, Setagaya Ku, Tokyo, Japan
[16] Waseda Univ, Adv Res Inst Sci & Engn, Shinjuku Ku, Tokyo, Japan
[17] Chiba Univ, Chiba, Japan
[18] Chungnam Natl Univ, Taejon, South Korea
[19] Ewha Womans Univ, Seoul, South Korea
[20] Univ Tokyo, Inst Phys & Math Universe, Kashiwa, Chiba, Japan
[21] Kyoto Univ, Sakyo Ku, Kyoto, Japan
[22] Kochi Univ, Kochi 780, Japan
[23] Univ Libre Brussels, Brussels, Belgium
[24] Univ Tokyo, Earthquake Res Inst, Bunkyo Ku, Tokyo 113, Japan
[25] Hiroshima City Univ, Hiroshima, Japan
[26] Natl Inst Radiol Sci, Chiba 260, Japan
[27] Ehime Univ, Matsuyama, Ehime, Japan