CLAS physics database search results Measurement E151M233 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.75 258 0.2395 0.5121 0.0335 0.65 246 0.0258 0.7339 0.03 0.65 258 0.1671 0.7306 0.0316 0.75 246 1.6244 0.8399 0.1023 0.75 258 -0.5749 0.5143 0.0458