[1] Univ Milan, Dipartimento Fis, Milan, Italy
[2] Ist Nazl Fis Nucl, Sez Milano, I-20133 Milan, Italy
[3] Univ Padua, Dipartimento Fis, Padua, Italy
[4] Univ W Scotland, Paisley, Renfrew, Scotland
[5] Ist Nazl Fis Nucl, Lab Nazl Legnaro, Padua, Italy
[6] Univ Valencia, CSIC, IFIC, E-46003 Valencia, Spain
[7] Ist Nazl Fis Nucl, Sez Padova, Padua, Italy
[8] Rudjer Boskovic Inst, Zagreb, Croatia
[9] Univ Camerino, I-62032 Camerino, Italy
[10] Ist Nazl Fis Nucl, Sez Perugia, Perugia, Italy
[11] Ist Nazl Fis Nucl, Sez Genova, I-16146 Genoa, Italy
[12] Polish Acad Sci, Niewodniczanski Inst Nucl Phys, Krakow, Poland
[13] Univ Cologne, Inst Kernphys, D-5000 Cologne, Germany
[14] Univ Turin, Dipartimento Fis Teor, I-10124 Turin, Italy
[15] Ist Nazl Fis Nucl, Sez Torino, Turin, Italy