[1] Peking Univ, Dept Phys, 209 Chengfu Rd, Beijing 100871, Peoples R China
[2] Peking Univ, State Key Lab Nucl Phys & Technol, 209 Chengfu Rd, Beijing 100871, Peoples R China
[3] Sun Yat Sen Univ, Sch Phys, 135 Xingang Xi Rd, Guangzhou 510275, Peoples R China