[1] European Gravitat Observ, I-56021 Cascina, PI, Italy
[2] Ist Nazl Fis Nucl, Sez Napoli, I-84084 Salerno, Italy
[3] Univ Salerno, I-84084 Salerno, Italy
[4] Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy
[5] Univ Pisa, I-56127 Pisa, Italy
[6] Ist Nazl Fis Nucl, Sez Perugia, I-06123 Perugia, Italy
[7] Univ Perugia, I-06123 Perugia, Italy
[8] Ist Nazl Fis Nucl, Sez Roma, I-00185 Rome, Italy
[9] Univ Naples Federico II, I-80126 Naples, Italy
[10] Univ Savoie, IN2P3 CNRS, Lab Annecy Le Vieux Phys Particules, F-74941 Annecy Le Vieux, France
[11] Ist Nazl Fis Nucl, Sez Napoli, I-80126 Naples, Italy
[12] Univ Paris Sud, IN2P3 CNRS, Lab Accelerateur Lineaire, F-91898 Orsay, France
[13] Natl Inst Subatom Phys, NL-1009 DB Amsterdam, Netherlands
[14] ESPCI 10, F-75005 Paris, France
[15] Ist Nazl Fis Nucl, Sez Firenze, I-50019 Sesto Fiorentino, Italy
[16] Univ Urbino, I-61029 Urbino, Italy
[17] Univ Florence, I-50121 Florence, Italy
[18] Observ Cote Azur, Dept Artemis, CNRS, F-06304 Nice, France
[19] Ist Nazl Fis Nucl, Sez Roma Tor Vergata, I-67100 Laquila, Italy
[20] Univ Roma Tor Vergata, I-00173 Rome, Italy
[21] Ist Nazl Fis Nucl, Sez Perugia, I-6123 Perugia, Italy
[22] Univ Perugia, I-6123 Perugia, Italy
[23] Ist Nazl Fis Nucl, Sez Pisa, I-53100 Siena, Italy
[24] Univ Siena, I-53100 Siena, Italy
[25] Univ Aquila, I-67100 Laquila, Italy
[26] CNRS, IN2P3, LMA, F-69622 Villeurbanne, Lyon, France
[27] Univ Roma La Sapienza, I-00185 Rome, Italy
[28] CNRS, ESPCI, F-75005 Paris, France
[29] INAF, Ist Fis Spazio Interplanetario, Trieste, Italy
[30] Vrije Univ Amsterdam, NL-1081 HV Amsterdam, Netherlands