[1] Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
[2] Univ Chinese Acad Sci, Beijing 100049, Peoples R China
[3] Univ Bonn, Helmholtz Inst Strahlen & Kernphys Theorie, D-53115 Bonn, Germany
[4] Univ Bonn, Bethe Ctr Theoret Phys, D-53115 Bonn, Germany
[5] Uppsala Univ, Box 516, S-75120 Uppsala, Sweden
[6] Natl Ctr Nucl Res, PL-02093 Warsaw, Poland