CLAS physics database search results Measurement E151M716 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 210 -0.0843 0.6547 0.0304 0.85 222 -0.0742 0.5808 0.0303