CLAS physics database search results Measurement E151M1916 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 294 0.0438 0.8124 0.0301 0.85 102 -0.9592 0.7073 0.0654 0.85 246 0.2679 0.7322 0.0341 0.85 258 0.2998 0.8158 0.0351