CLAS physics database search results Measurement E151M1000 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.75 102 -1.0754 0.5971 0.0841 0.75 258 0.5413 0.8125 0.0497 0.75 318 -0.7092 0.5831 0.0599 0.85 234 0.0262 0.6811 0.0301 0.85 258 0.3314 0.799 0.0386 0.85 270 -0.3022 0.6929 0.0373