[1] Max Planck Inst Phys & Astrophys, D-80805 Munich, Germany
[2] Univ Wurzburg, D-97074 Wurzburg, Germany
[3] Inst Fis Altes Energies, E-08193 Barcelona, Spain
[4] ETH, CH-8093 Zurich, Switzerland
[5] Univ Complutense, E-28040 Madrid, Spain
[6] Univ Autonoma Barcelona, E-08193 Barcelona, Spain
[7] Univ Padua, Ist Nazl Fis Nucl, I-35131 Padua, Italy
[8] Univ Dortmund, D-44227 Dortmund, Germany
[9] Univ Lodz, PL-90236 Lodz, Poland
[10] Univ Barcelona, E-08028 Barcelona, Spain
[11] Yerevan Phys Inst, Yerevan 375036, Armenia
[12] Tuorla Observ, FI-21500 Piikkio, Finland
[13] Inst Astrofis Canarias, E-38200 San Cristobal la Laguna, Spain
[14] Univ Udine, Ist Nazl Fis Nucl, I-33100 Udine, Italy
[15] Univ Siena, Ist Nazl Fis Nucl, I-53100 Siena, Italy
[16] Univ Calif Davis, Davis, CA 95616 USA