[1] Univ Sofia St Kliment Ohridski, Sofia, Bulgaria
[2] Dipartimento Interateno Fis, Bari, Italy
[3] Sez INFN, Bari, Italy
[4] Dipartimento Fis Teorica & Nucl, Naples, Italy
[5] Sez INFN, Naples, Italy
[6] Univ Pavia, Dipartimento Fis Nucl & Teor, I-27100 Pavia, Italy
[7] Sez INFN, Pavia, Italy
[8] Bulgarian Acad Sci, INRNE, Sofia, Bulgaria
[9] Peking Univ, Beijing 100871, Peoples R China