[1] Univ Aveiro, I3N, Dept Phys, P-3810193 Aveiro, Portugal
[2] Univ Calif Berkeley, Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA
[3] Univ Liverpool, Dept Phys, Liverpool L69 7ZE, Merseyside, England
[4] CERN RD 51 Collaborat, Geneva, Switzerland