[1] SCUOLA NORMALE SUPER,I-56100 PISA,ITALY
[2] UNIV LONDON WESTFIELD COLL,DEPT PHYS,LONDON NW3 7ST,ENGLAND
[3] CNR,IST FIS GEN,TURIN,ITALY
[4] CNR,IST COSMOGEOFIS,TURIN,ITALY
[5] IST NAZL FIS NUCL,DIPARTIMENTO FIS,MILAN,ITALY
[6] IST NAZL FIS NUCL,IST FIS,TRIESTE,ITALY
[7] SCUOLA INT SUPER STUDI AVANZATI,TRIESTE,ITALY
[8] IST NAZL FIS NUCL,LAB FRASCATI,FRASCATI,ITALY
[9] UNIV SOUTHAMPTON,DEPT PHYS,SOUTHAMPTON SO9 5NH,HANTS,ENGLAND