CLAS physics database search results Measurement E151M681 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.75 246 -0.4161 0.6921 0.0393 0.85 210 -0.2338 0.7494 0.0332 0.85 234 1.0884 0.7411 0.073 0.95 102 -0.2891 0.6811 0.0348