CLAS physics database search results Measurement E151M20 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.55 258 0.2722 0.5728 0.0431 0.65 246 -0.2013 0.4378 0.0377 0.65 258 0.2702 0.4959 0.043 0.65 270 0.2522 0.5343 0.0415 0.75 258 0.0698 0.5396 0.031