[1] Shanghai Jiao Tong Univ, Tsung Dao Lee Inst, 800 Dongchuan Rd, Shanghai 200240, Peoples R China
[2] Shanghai Jiao Tong Univ, Sch Phys & Astron, 800 Dongchuan Rd, Shanghai 200240, Peoples R China
[3] Univ Massachusetts, Amherst Ctr Fundamental Interact, Dept Phys, Amherst, MA 01003 USA
[4] CALTECH, Kellogg Radiat Lab, Pasadena, CA 91125 USA