CLAS physics database search results Measurement E151M450 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.85 222 0.1669 0.7354 0.0317 0.85 234 0.1721 0.6212 0.0318 0.85 246 -0.1888 0.6443 0.0322 0.75 234 2.0044 1.3898 0.1244 0.85 246 -0.0132 0.8727 0.03