Univ Nantes, SUBATECH, F-44035 Nantes, France.^Forschungszentrum Karlsruhe, Inst Kernphys, D-76021 Karlsruhe, Germany.^NYU, Dept Phys, New York, NY 10003 USA.^Huazhong Normal Univ, Inst Particle Phys, Wuhan, Peoples R China.^Univ Karlsruhe, Inst Expt Kernphys, D-7500 Karlsruhe, Germany.