[1] Johannes Gutenberg Univ Mainz, Inst Kernphys, D-55128 Mainz, Germany
[2] Johannes Gutenberg Univ Mainz, PRISMA Cluster Excellence, D-55128 Mainz, Germany
[3] Fermilab Natl Accelerator Lab, Theoret Phys Dept, POB 500, Batavia, IL 60510 USA
[4] Argonne Natl Lab, Phys Div, Argonne, IL 60439 USA
[5] INFN, TIFPA Trento Inst Fundamental Phys & Applicat, I-38123 Trento, Italy