[1] Univ Bari, Dipartmento Fis, I-70126 Bari, Italy
[2] Ist Nazl Fis Nucl, I-70126 Bari, Italy
[3] Univ Padua, I-35100 Padua, Italy
[4] Ist Nazl Fis Nucl, Padua, Italy
[5] Univ Perugia, I-06100 Perugia, Italy
[6] Ist Nazl Fis Nucl, I-06100 Perugia, Italy
[7] Univ Catania, I-95124 Catania, Italy
[8] Ist Nazl Fis Nucl, I-95129 Catania, Italy