CLAS physics database search results Measurement E151M1083 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 258 0.6119 0.8974 0.0539 0.85 270 -0.0078 0.7517 0.03 0.85 294 -0.5444 0.7383 0.0498