CLAS physics database search results Measurement E151M2809 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.55 222 -0.7469 0.2209 0.0335 0.55 234 -0.0875 0.2349 0.0301 0.65 222 0.1434 0.2557 0.0301 0.65 234 -0.0113 0.2288 0.0301 0.75 222 -0.3724 0.3079 0.0309 0.75 234 -0.0588 0.2716 0.03