[1] St Petersburg State Univ, Dept Phys, 7-9 Univ Nab, St Petersburg 199034, Russia
[2] Natl Res Ctr, Petersburg Nucl Phys Inst, Kurchatov Inst, Gatchina 188300, Russia
[3] Chinese Acad Sci, Inst Modern Phys, Lanzhou 730000, Peoples R China
[4] Univ Chinese Acad Sci, Beijing 100049, Peoples R China