CLAS physics database search results Measurement E151M402 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.55 222 -1.1442 0.6398 0.0752 0.65 234 0.4262 1.1897 0.0395 0.75 222 0.0534 0.9739 0.0302