[1] GSI Darmstadt, Gesell Schwerionenforsch, D-64291 Darmstadt, Germany
[2] Univ Bielefeld, Fak Phys, D-33501 Bielefeld, Germany
[3] Univ Wroclaw, Inst Theoret Phys, PL-50204 Wroclaw, Poland
[4] Heidelberg Univ, Inst Phys, D-69120 Heidelberg, Germany