[1] Russian Acad Sci, Inst High Energy Dent, Moscow 127412, Russia
[2] Univ Rostock, Fachbereich Phys, D-18051 Rostock, Germany
[3] Humboldt Univ, Inst Phys, D-10115 Berlin, Germany
[4] Ernst Moritz Arndt Univ Greifswald, Fachbereich Phys, D-17489 Greifswald, Germany