CLAS physics database search results Measurement E151M694 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.65 294 -0.4068 0.645 0.039 0.85 102 -0.9228 0.5302 0.0639 0.85 246 0.938 0.6717 0.0647 0.85 258 1.383 0.7348 0.0898