CLAS physics database search results Measurement E151M718 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.75 234 0.9199 0.7372 0.0638 0.75 282 -0.4306 0.6675 0.0399 0.85 222 1.9026 0.7422 0.1202