CLAS physics database search results Measurement E151M2124 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.85 222 -0.3931 0.9569 0.047 0.85 234 0.7171 0.9273 0.0724 0.65 294 -0.8491 0.7224 0.0629 0.75 210 -2.6075 0.7919 0.1723 0.85 102 0.3937 0.8695 0.0394 0.85 234 0.456 1.0008 0.0422