CLAS physics database search results Measurement E151M181 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.35 42 0.2659 0.8349 0.0426 0.35 54 1.3715 0.8386 0.1589 0.45 54 0.4238 0.7534 0.0568 0.45 222 -0.438 0.7191 0.0582 0.55 210 0.3724 0.7932 0.0519 0.55 234 0.3796 0.7097 0.0526 0.75 222 1.6925 0.7261 0.1949 0.75 234 -0.4988 0.6047 0.0642 0.85 222 0.4665 0.6579 0.061 0.85 234 -0.2332 0.6377 0.04