CLAS physics database search results Measurement E151M2903 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.55 234 0.7258 0.235 0.0333 0.65 222 -0.313 0.2904 0.0306 0.75 222 0.7238 0.2162 0.0333 0.75 246 0.1678 0.3637 0.0302