[1] Univ Roma Tor Vergata, Dip Fis, I-00133 Rome, Italy
[2] Ist Nazl Fis Nucl, Sez Roma, I-00133 Rome, Italy
[3] Univ Roma La Sapienza, Dip Fis, I-00185 Rome, Italy
[4] Ist Nazl Fis Nucl, Sez Roma, I-00185 Rome, Italy
[5] Ist Nazl Fis Nucl, Lab Nazl Gran Sasso, Assergi, Italy
[6] Chinese Acad, IHEP, Beijing 100039, Peoples R China