[1] Aarhus Univ, Dept Phys & Astron, DK-8000 Aarhus C, Denmark
[2] Joint Inst Nucl Res, Dubna 141980, Russia
[3] Univ Catholique Louvain, B-1348 Louvain, Belgium
[4] Russian Res Ctr, SV Kurashov Med Inst, Moscow 123182, Russia
[5] Paul Scherrer Inst, CH-5232 Villigen, Switzerland