1. Department of Physics, University of Florence, I-50019 Sesto Fiorentino, Florence, Italy.
2. Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Florence, I-50019 Sesto Fiorentino, Florence, Italy.
3. Department of Physics, University of Naples “Federico II,” I-80126 Naples, Italy.
4. INFN, Sezione di Naples, I-80126 Naples, Italy.
5. Lebedev Physical Institute, RU-119991, Moscow, Russia.
6. Department of Physics, University of Bari, I-70126 Bari, Italy.
7. INFN, Sezione di Bari, I-70126 Bari, Italy.
8. INFN, Sezione di Trieste, I-34149 Trieste, Italy.
9. Ioffe Physical Technical Institute, RU-194021 St. Petersburg, Russia.
10. INFN, Sezione di Rome “Tor Vergata,” I-00133 Rome, Italy.
11. Department of Physics, University of Rome “Tor Vergata,” I-00133 Rome, Italy.
12. Moscow Engineering and Physics Institute, RU-11540 Moscow, Russia.
13. Department of Physics, Kungliga Tekniska Högskolan, and the Oskar Klein Centre for Cosmoparticle Physics, AlbaNova University Centre, SE-10691 Stockholm, Sweden.
14. Istituto di Fisica Applicata Nello Carrara, I-50019 Sesto Fiorentino, Florence, Italy.
15. Department of Physics, University of Trieste, I-34147 Trieste, Italy.
16. Department of Physics, Universität Siegen, D-57068 Siegen, Germany.
17. INFN, Laboratori Nazionali di Frascati, Via Enrico Fermi 40, I-00044 Frascati, Italy.