1. Shanghai Institute of Ceramics, Chinese Academy of Sciences, 588 He-Shuo Road, Shanghai 201899, P. R. China
2. Physics Experiment Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
3. Institute of Physics of the Czech Academy of Sciences, Cukrovarnicka 10/112, Prague 16200, Czech Republic
4. Northwest Institute of Nuclear Technology, Xi’an 710024, P. R. China