[1] Univ Naples, Dipartimento Fis, I-80125 Naples, Italy
[2] Ist Nazl Fis Nucl, I-80125 Naples, Italy
[3] Univ Bari, Dipartimento Fis, I-70126 Bari, Italy
[4] Ist Nazl Fis Nucl, I-70126 Bari, Italy
[5] Univ Bologna, Dipartimento Fis, I-40126 Bologna, Italy
[6] Ist Nazl Fis Nucl, I-40126 Bologna, Italy
[7] Boston Univ, Dept Phys, Boston, MA 02215 USA
[8] CALTECH, Pasadena, CA 91125 USA
[9] Drexel Univ, Dept Phys, Philadelphia, PA 19104 USA
[10] Ist Nazl Fis Nucl, Lab Nazl Frascati, I-00044 Frascati, Roma, Italy
[11] Ist Nazl Fis Nucl, Lab Nazl Gran Sasso, I-67010 Assergi, Laquila, Italy
[12] Indiana Univ, Dept Phys, Bloomington, IN 47405 USA
[13] Indiana Univ, Dept Astron, Bloomington, IN 47405 USA
[14] Univ Aquila, Dipartimento Fis, I-67100 Laquila, Italy
[15] Ist Nazl Fis Nucl, I-67100 Laquila, Italy
[16] Univ Lecce, Dipartimento Fis, I-73100 Lecce, Italy
[17] Ist Nazl Fis Nucl, I-73100 Lecce, Italy
[18] Univ Michigan, Dept Phys, Ann Arbor, MI 48109 USA
[19] Univ Pisa, Dipartimento Fis, I-56010 Pisa, Italy
[20] Ist Nazl Fis Nucl, I-56010 Pisa, Italy
[21] Univ Roma La Sapienza, Dipartimento Fis, I-00185 Rome, Italy
[22] Ist Nazl Fis Nucl, I-00185 Rome, Italy
[23] Texas A&M Univ, Dept Phys, College Stn, TX 77843 USA
[24] Univ Turin, Dipartimento Fis Sperimentale, I-10125 Turin, Italy
[25] Ist Nazl Fis Nucl, I-10125 Turin, Italy
[26] Univ Mohamed 1, Fac Sci, LPTP, Oujda, Morocco
[27] Univ Roma Tre, Dipartimento Fis, I-00146 Rome, Italy
[28] Ist Nazl Fis Nucl, Sez Roma Tre, I-00146 Rome, Italy
[29] Univ Basilicata, I-85100 Potenza, Italy
[30] Ist Nazl Fis Nucl, I-20133 Milan, Italy
[31] CNR, Ist IASF, I-40129 Bologna, Italy
[32] Univ Trieste, I-34100 Trieste, Italy
[33] Ist Nazl Fis Nucl, I-34100 Trieste, Italy
[34] Univ Rome, Dipartimento Energet, I-00185 Rome, Italy
[35] Inst Space Sci, Bucharest 76900, Romania
[36] Penn State Univ, Dept Phys, University Pk, PA 16801 USA
[37] Univ Calabria, Dipartimento Fis, I-87036 Arcavacata Di Rende, Cosenza, Italy
[38] RPD, PINSTECH, Islamabad, Pakistan