CLAS physics database search results Measurement E151M2125 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 126 0.9785 0.9097 0.0948 0.85 246 -0.0622 0.9317 0.0305 0.75 222 -0.5048 0.9753 0.0445 0.85 90 1.2737 0.8653 0.0881 0.85 234 -1.3274 0.9736 0.0914 0.85 246 -1.7564 0.9308 0.1181