[1] Helmholtz Inst Jena, Frobelstieg 3, D-07743 Jena, Germany
[2] GSI Helmholtzzentrum Schwer Forschung, Planckstr 1, D-64291 Darmstadt, Germany
[3] Friedrich Schiller Univ Jena, Theoret Phys Inst, Abbe Ctr Photon, Max Wien Pl 1, D-07743 Jena, Germany
[4] Ludwig Maximilians Univ Munchen, Coulombwall 1, D-85748 Garching, Germany