1. Beihang University, International Research Center for Nuclei and Particles in the Cosmos, Beijing 100191, China
2. Beihang University, School of Physics and Nuclear Energy Engineering, Beijing 100191, China
3. Kyungpook National University, Department of Physics, Daegu 702-701, Korea
4. Pohang University of Science and Technology, Department of Physics, Pohang 790-784, Korea