[1] Fermilab Natl Accelerator Lab, Batavia, IL 60510 USA
[2] Univ Wisconsin, Phys Sci Lab, Stoughton, WI 53589 USA
[3] Penn State Univ, Dept Astron & Astrophys, University Pk, PA 16802 USA
[4] Penn State Univ, Dept Phys, University Pk, PA 16802 USA
[5] Univ Alberta, Dept Phys, Edmonton, AB, Canada
[6] Univ Wisconsin, Dept Phys, Madison, WI 53706 USA
[7] Univ Sheffield, Dept Phys & Astron, Sheffield S3 7RH, S Yorkshire, England