[1] Stanford Linear Accelerator Center, 2575 Sand Hill Rd., Menlo Park, CA 94025, United States
[2] University of Massachusetts, Amherst, MA 01003, United States
[3] NASA/Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States
[4] SCIPP, University of California at Santa Cruz, Santa Cruz, CA 95064, United States
[5] Stanford University, Stanford, CA 94305, United States
[6] PCC - College de France, 11, Place Marcelin Berthelot, 75231 Paris Cedex 05, France
[7] U.S. Naval Research Laboratory, 4555 Overlook Ave. S.W., Washington, DC 20375, United States
[8] University of Washington, Seattle, WA 98195, United States
[9] CEA, DSM/DAPNIA, Centre d'Etudes de Saclay, Gif-sur-Yvette, France
[10] Dept. of Physics, Hiroshima University, Higashi-Hiroshima, Hiroshima 739, Japan
[11] Royal Institute of Technology, Department of Physics, SE-100 44 Stockholm, Sweden