1. Department of Physics, University of California, Berkeley, California 94720, USA
2. Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
3. Facility for Rare Isotope Beams, Michigan State University, East Lansing, Michigan 48824, USA;
4. Cyclotron Institute and Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA
5. Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany
6. ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany