[1] Lab Annecy le Vieux Phys Particules, Annecy Le Vieux, France
[2] EGO, Cascina, Pi, Italy
[3] Ist Nazl Fis Nucl, Sez Firenze Urbino, Sesto Fiorentino, Italy
[4] Univ Florence, Florence, Italy
[5] Univ Urbino, Urbino, Italy
[6] Ist Nazl Fis Nucl, Lab Nazl Frascati, Frascati, Rm, Italy
[7] LMA, Lyon, France
[8] Ist Nazl Fis Nucl, Sez Napoli, Naples, Italy
[9] Univ Naples Federico II, Naples, Italy
[10] Univ Salerno, Fisciano, Sa, Italy
[11] Observ Cote Azur, Dept Artemis, BP 42209, F-06304 Nice 4, France
[12] Univ Paris Sud, CNRS, IN2P3, LAL, Orsay, France
[13] ESPCI, Paris, France
[14] Ist Nazl Fis Nucl, Sez Perugia, Perugia, Italy
[15] Univ Perugia, Perugia, Italy
[16] Ist Nazl Fis Nucl, Sez Pisa, Pisa, Italy
[17] Univ Pisa, Pisa, Italy
[18] Ist Nazl Fis Nucl, Sez Roma, Rome, Italy
[19] Univ Roma La Sapienza, Rome, Italy