[1] Univ Durham, Dept Phys, Durham DH1 3LE, England
[2] Univ Durham, Inst Particle Phys Phenomenol, Durham DH1 3LE, England
[3] Univ Helsinki, Dept Phys, Helsinki, Finland
[4] Helsinki Inst Phys, Helsinki, Finland
[5] Petersburg Nucl Phys Inst, St Petersburg 188300, Russia