1. Department of Physics; University of Rome “Tor Vergata” and Istituto Nazionale di Fisica Nucleare section of Roma2; Rome Italy
2. Moscow Engineering Physics Institute; Moscow Russia
3. Department of Physics; University of Trieste and Istituto Nazionale di Fisica Nucleare section of Trieste; Trieste Italy
4. Department of Physics; University of Bari and Istituto Nazionale di Fisica Nucleare section of Bari; Bari Italy
5. Department of Physics; University of Florence and Istituto Nazionale di Fisica Nucleare section of Florence; Florence Italy
6. Istituto Nazionale di Fisica Nucleare National Laboratories of Frascati; Frascati Italy
7. Institute of Applied Physics “Nello Carrara”, CNR; Florence Italy