[1] DESY, D-2000 HAMBURG 52, GERMANY
[2] UNIV MAINZ, INST PHYS, D-6500 MAINZ, GERMANY
[3] UNIV KIEL, INST THEORET PHYS, D-2300 KIEL 1, GERMANY
[4] UNIV HANOVER, INST THEORET PHYS, D-3000 Hannover, GERMANY
[5] UNIV HAMBURG, INST THEORET PHYS 2, D-2000 HAMBURG 50, GERMANY