CLAS physics database search results Measurement E151M213 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.65 282 -0.7875 0.4386 0.0573 0.85 102 0.5642 0.5022 0.0461 0.55 282 -0.7219 0.4593 0.0528