CLAS physics database search results Measurement E151M724 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.75 210 -0.1374 0.7111 0.0312 0.75 270 -0.873 0.6418 0.0612 0.85 222 0.6681 0.7953 0.0507