CLAS physics database search results Measurement E151M1937 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 222 -0.5564 0.8367 0.0451 0.75 282 -0.0749 0.7594 0.0303 0.85 126 -0.1045 0.8852 0.0307 0.85 210 -0.3871 0.8655 0.0381 0.85 222 -0.5071 0.8463 0.0429