CLAS physics database search results Measurement E151M2902 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 234 0.4752 0.2515 0.0315 0.75 234 0.3717 0.3777 0.0309 0.85 222 -0.1138 0.3793 0.0301 0.85 246 -0.181 0.4011 0.0302