1. Department of Physics, Nanjing University, Nanjing 210093, P. R. China
2. Department of Physics, Nanjing Normal University, Nanjing 210023, P. R. China
3. Nanjing Proton Research and Design Center, Nanjing 210093, P. R. China
4. Department of Physics, Anhui Normal University, Wuhu 241000, P. R. China
5. Joint Center for Particle, Nuclear Physics and Cosmology, Nanjing 210093, P. R. China