CLAS physics database search results Measurement E151M723 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.75 78 1.2518 0.8133 0.0822 0.75 210 0.6682 0.7447 0.0507 0.75 258 -0.6345 0.6854 0.0491 0.75 270 -1.1283 0.5715 0.0752 0.75 282 0.8553 0.7485 0.0603