CLAS physics database search results Measurement E151M1643 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 222 -0.2284 0.9762 0.033 0.75 210 -0.7896 1.0258 0.056 0.75 234 -0.5045 0.9722 0.0426 0.55 42 -1.0707 1.3397 0.0691 0.65 210 -1.2497 1.1058 0.0786 0.75 234 -1.2256 1.2914 0.0773 0.85 222 2.1782 0.8289 0.1302