CLAS physics database search results Measurement E151M460 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.75 246 0.849 1.6614 0.0593 0.85 222 -0.6351 0.8202 0.0486 0.65 234 1.2379 0.6995 0.0823 0.75 234 0.8665 0.6868 0.0615