CLAS physics database search results Measurement E151M2256 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.55 90 0.9984 0.8754 0.0784 0.75 270 0.8375 0.8676 0.0677 0.75 282 0.5673 0.9134 0.0509 0.85 258 -1.6034 0.8364 0.1201 0.85 270 1.4268 0.7541 0.1077 0.85 294 -0.3258 0.8024 0.0382 0.85 306 0.6092 0.7334 0.0534 0.85 318 1.3914 0.7692 0.1053 0.85 330 1.3031 0.7395 0.0991