1. Physics Branch, Wu C.‐S. Centre, 24, Lane 260, Section 1, Muzha Road, Taipei, Taiwan 116, China
2. P.O. Box 39, Toudiban, Xihong Road, Wulumuqi 830000, China
3. College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China
4. Department of Physics, Xinjiang Normal University, Wulumuqi 830054, China