[1] Old Dominion Univ, Dept Phys, Norfolk, VA 23529 USA
[2] Jefferson Lab, 12000 Jefferson Ave, Newport News, VA 23606 USA
[3] Zhejiang Univ, Zhejiang Inst Modern Phys, Dept Phys, Hangzhou 310027, Zhejiang, Peoples R China
[4] Univ Torino, Dipartimento Fis, Via P Giuria 1, I-10125 Turin, Italy