CLAS physics database search results Measurement E151M418 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.65 222 1.0869 0.7415 0.0737 0.85 234 0.2151 0.6986 0.0328 0.65 246 -0.4404 0.8561 0.04 0.65 258 -0.7654 0.8029 0.055 0.75 246 -0.1461 0.9958 0.0313