CLAS physics database search results Measurement E151M417 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 234 0.4636 0.7095 0.0415 0.65 246 0.5354 1.2271 0.044 0.75 246 -0.6324 0.8143 0.0485