CLAS physics database search results Measurement E151M21 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.55 258 -0.7658 0.3551 0.0921 0.55 270 -0.3007 0.435 0.0455 0.65 234 -0.1744 0.5039 0.036 0.65 246 -0.425 0.3646 0.0569 0.65 258 0.4059 0.4426 0.0551 0.65 270 0.0205 0.4254 0.0301 0.75 174 0.2691 0.5499 0.0429 0.75 246 0.6338 0.4001 0.0781 0.75 258 0.3586 0.4385 0.0506