CLAS physics database search results Measurement E151M650 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 234 -0.8817 0.6315 0.0617 0.85 246 -0.8309 0.6627 0.059 0.95 222 0.8116 0.7953 0.058 0.95 258 0.1734 0.5862 0.0318