CLAS physics database search results Measurement E151M60 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.65 234 0.5197 0.6147 0.0663 0.65 246 -0.7134 0.4509 0.0865 0.75 246 0.32 0.651 0.0472