[1] Univ Minho, Dept Fis, Lab Instrumentacao & Fis Expt Particulas, P-4710057 Braga, Portugal
[2] Univ Porto, Fac Ciencias, Dept Fis & Astron, P-4169007 Oporto, Portugal
[3] TU Dortmund, Lehrstuhl Expt Phys 4, Otto Hahn Str 4a, D-44227 Dortmund, Germany
[4] Univ Gottingen, Phys Inst 2, Friedrich Hund Pl 1, D-37077 Gottingen, Germany