1. Department of Physics, Stanford University, Stanford, California 94305, USA
2. SLAC National Accelerator Laboratory/Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, California 94025, USA
3. Fermi National Accelerator Laboratory, Center for Particle Astrophysics, Batavia, Illinois 60510, USA
4. Department of Physics, University of Illinois at Urbana-Champaign, Champaign, Illinois 61820, USA
5. Department of Physics, San Diego State University, San Diego, California 92182, USA
6. Department of Physics, Santa Clara University, Santa Clara, California 95053, USA