1. Physics Department, Faculty of Science, University of Zagreb, Croatia
2. State Key Laboratory for Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871, People's Republic of China
3. Dipartimento di Fisica dell'Università degli Studi, via Celoria 16, 20133 Milano, Italy
4. INFN, Sezione di Milano, via Celoria 16, 20133 Milano, Italy
5. Institut de Physique Nucléaire, IN2P3-GNRS/Université Paris-Sud, 91406 Orsay, France
6. School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, People's Republic of China