1. Institute of Physics, Graduate School of Arts and Sciences, University of Tokyo, Meguro, Tokyo 153-8901, Japan
2. Atomic Physics Research Unit, RIKEN, Wako, Saitama 351-0198, Japan
3. Department of Applied Physics, Tokyo Univeristy of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
4. Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashihiroshima, Hiroshima 739-8530, Japan
5. Dipartmento di Ingegneria dell’Informazione, Università di Brescia, Brescia 25133, Italy
6. INFN, Gruppo Collegato di Brescia, Brescia 25133, Italy
7. CERN, Genève 1211, Switzerland
8. Ulmer Initiative Research Unit, RIKEN, Wako, Saitama 351-0198, Japan