CLAS physics database search results Measurement E151M3466 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 270 0.4159 0.23 0.0311 0.85 306 0.2682 0.2535 0.0305 0.85 318 0.2463 0.2614 0.0304