1. Institute of Physics, National Chiao-Tung University, Hsinchu 300, Taiwan
2. Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 106, Taiwan
3. Institute for Astrophysics, National Taiwan University, Taipei 106, Taiwan
4. Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
5. SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
6. Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2G7, Canada