[1] UNIV ROMA TOR VERGATA, DIPARTIMENTO FIS, ROME, ITALY
[2] INFN, ROME, ITALY
[3] UNIV COMPLUTENSE MADRID, DEPT FIS TEOR, E-28040 MADRID, SPAIN
[4] UNIV AUTONOMA MADRID, DEPT FIS TEOR, E-28034 MADRID, SPAIN
[5] FYZ USTAV AKAD PRAGUE, PRAGUE, CZECHOSLOVAKIA
[6] UNIV ROMA 1, DIPARTIMENTO FIS, ROME, ITALY
[7] INFN, ROME, ITALY
[8] UNIV ZARAGOZA, FAC CIENCIAS, SERV INTRUMENTAC ELECTR, ZARAGOZA, SPAIN