CLAS physics database search results Measurement E151M3380 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 114 -0.1899 0.2322 0.0302 0.85 126 -0.1056 0.2522 0.0301