CLAS physics database search results Measurement E151M3166 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 270 -0.5303 0.1979 0.0318 0.85 126 -0.2856 0.2662 0.0305