CLAS physics database search results Measurement E151M1932 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.55 258 -0.4069 0.8363 0.0388 0.65 198 -1.6548 0.7836 0.1047 0.75 258 -0.995 0.8482 0.0673 0.75 270 -0.6166 0.7673 0.0479 0.75 282 -0.5726 0.7036 0.0459 0.85 138 -0.341 0.8307 0.0364 0.85 210 -1.0666 0.7835 0.0713