[1] Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China
[2] Tsinghua Univ, Ctr High Energy Phys, Beijing 100084, Peoples R China
[3] Hong Kong Univ Sci & Technol, Dept Phys, Kowloon, Clear Water Bay, Hong Kong, Peoples R China
[4] Univ Calif Santa Barbara, Kavli Inst Theoret Phys, Santa Barbara, CA 93106 USA
[5] Univ Chicago, Dept Phys, Chicago, IL 60637 USA
[6] Univ Chicago, Enrico Fermi Inst, Chicago, IL 60637 USA
[7] Univ Chicago, Kavli Inst Cosmol Phys, Chicago, IL 60637 USA
[8] Stockholm Univ, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden
[9] Stockholm Univ, Dept Phys, S-10691 Stockholm, Sweden