CLAS physics database search results Measurement E151M61 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.65 246 0.3609 0.6251 0.0509 0.75 234 -0.3688 0.6406 0.0516 0.75 246 0.4761 0.6355 0.0619 0.75 258 -0.1242 0.6164 0.0332