CLAS physics database search results Measurement E151M2412 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.85 102 0.7199 0.9703 0.0602 0.85 210 -1.4738 1.0105 0.111 0.85 222 -1.3155 0.8935 0.1 0.95 198 -1.7099 0.8939 0.1276