[1] IBM Corp, Thomas J Watson Res Ctr, Yorktown Heights, NY 10598 USA
[2] Indiana Univ, Dept Phys, Bloomington, IN 47405 USA
[3] Univ Calif Los Alamos Natl Lab, GrpT8, Los Alamos, NM 87545 USA
[4] KEK, High Energy Accelerator Res Org, Tsukuba, Ibaraki 3050801, Japan
[5] Univ Rome La Sapienza, Ist Fis G Marconi, I-00185 Rome, Italy
[6] Columbia Univ, Dept Phys, New York, NY 10027 USA