1. Gesellschaft für Schwerionenforschung mbH, Planckstr. 1, D-64291 Darmstadt, Germany
2. Frankfurt Institute for Advanced Studies, Universität Frankfurt, D-60438 Frankfurt am Main, Germany
3. Joint Institute for Nuclear Research, RU-141980 Dubna, Moscow Region, Russia
4. Dipartimento di Fisica dell'Universitá di Trento, via Sommarive 14, I–38050 Povo, Trento, Italy