[1] Univ Lecce, NCR INFM, NNL, CACT, I-73100 Lecce, Italy
[2] Univ Lecce, Fac Engn, I-73100 Lecce, Italy
[3] Univ Clermont Ferrand, CNRS UMR 6533, IN2P3, Lab Phys Corpusculaire Clermont Ferrand, Clermont Ferrand, France
[4] Univ Naples Federico II, Naples, Italy
[5] Univ W England, Fac Comp Engn & Math Sci, Bristol BS16 1QY, Avon, England