1. School of Physics, Liaoning University, No. 66, Chongshan Middle Road, Huanggu District, Shenyang 110036, P. R. China
2. State Key Laboratory of Particle Detection and Electronics, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing 100049, P. R. China
3. University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, P. R. China
4. Department of Engineering Physics, Tsinghua University, Hai Dian District, Beijing 100084, P. R. China