CLAS physics database search results Measurement E151M2880 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 222 0.5127 0.2171 0.0317 0.55 222 0.9239 0.168 0.0352 0.75 210 -0.2741 0.4042 0.0305