CLAS physics database search results Measurement E151M2846 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.55 222 0.532 0.3164 0.0318 0.65 234 0.792 0.2049 0.0339 0.75 222 -0.3644 0.3629 0.0309