CLAS physics database search results Measurement E151M1890 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 222 -0.5666 0.9038 0.0456 0.75 198 0.0678 0.9294 0.0303 0.75 210 -1.5141 0.7868 0.0965 0.85 126 -0.2769 0.9109 0.0344 0.85 138 -0.9699 0.8614 0.066 0.85 222 -0.357 0.7598 0.037