CLAS physics database search results Measurement E151M467 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.95 114 0.2176 0.4907 0.0328 0.95 126 -0.1934 0.4709 0.0322 0.95 138 -0.1277 0.4429 0.031