[1] National Central University, Chungli 320, Taiwan
[2] INFN-Sezione di Perugia, I-06100 Perugia, Italy
[3] University of Geneva, CH-1211 Geneva 4, Switzerland
[4] GSI, Planckstrasse 1, D-64291 Darmstadt, Germany
[5] ETH Zurich, CH-8093 Zurich, Switzerland
[6] IMT and EPPG, Bucharest, Romania