1. Department of Physics, Stanford University, Stanford, California 94305, USA
2. Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
3. Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada
4. Institut für Experimentalphysik, Universität Hamburg, 22761 Hamburg, Germany
5. SLAC National Accelerator Laboratory/Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, California 94025, USA
6. Fermi National Accelerator Laboratory, Center for Particle Astrophysics, Batavia, Illinois 60510, USA
7. Kavli Institute for Cosmological Physics, University of Chicago, Chicago, Illinois 60637, USA
8. Department of Physics, Santa Clara University, Santa Clara, California 95053, USA