CLAS physics database search results Measurement E151M1871 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 102 -0.547 0.992 0.0447 0.75 234 -0.2168 0.9296 0.0327 0.85 78 -0.3037 0.9439 0.0352 0.85 246 0.1978 0.7972 0.0323 0.85 258 -0.695 0.8518 0.0517 0.95 222 0.0161 0.7954 0.03 0.95 234 0.6116 0.8224 0.0477