[1] Ecole Polytech, CNRS, IN2P3, Lab Leprince Ringuet, F-91128 Palaiseau, France
[2] Washington Univ, Dept Phys, St Louis, MO 63130 USA
[3] Max Planck Inst Kernphys, D-69029 Heidelberg, Germany
[4] Landessternwarte Heidelberg, D-69117 Heidelberg, Germany
[5] CEN Bordeaux Gradignan, F-33175 Gradignan, France
[6] Univ Paris 06 & 07, IN2P3, CNRS, Lab Phys Nucl Hautes Energies, F-75231 Paris, France