1. Department of Physics, University of California, Berkeley, Berkeley, California 94720, USA;
2. Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94549, USA
3. Institute for Nuclear and Particle Physics, Technische Universität Dresden, 01069 Dresden, Germany
4. Nuclear Physics Division, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
5. Institute of Space Sciences (ICE-CSIC), 08193 Barcelona, Spain
6. Institut d'Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
7. Max Planck Institute for Astronomy, 69117 Heidelberg, Germany