CLAS physics database search results Measurement E151M800 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 102 0.3935 0.7284 0.0396 0.85 258 -0.2104 0.6397 0.033 0.85 282 0.5839 0.6769 0.0487 0.85 294 -0.3398 0.5726 0.0374 0.95 294 -0.4401 0.9425 0.0416