[1] UNIV CALIF BERKELEY, DEPT PHYS, BERKELEY, CA 94720 USA
[2] UNIV CALIF BERKELEY, DEPT MAT SCI & MINERAL ENGN, BERKELEY, CA 94720 USA
[3] UNIV CALIF SANTA BARBARA, DEPT PHYS, SANTA BARBARA, CA 93106 USA
[4] LAWRENCE BERKELEY LAB, BERKELEY, CA 94720 USA
[5] CENS, SERV PHYS PARTICULES, DEPT ASTROPHYS, F-91191 GIF SUR YVETTE, FRANCE
[6] UNIV BRITISH COLUMBIA, DEPT PHYS, VANCOUVER V6T 1Z1, BC, CANADA
[7] COLL FRANCE, PHYS CORPUSCULAIRE LAB, F-75231 PARIS, FRANCE