CLAS physics database search results Measurement E151M3168 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 210 -0.1526 0.2602 0.0302 0.75 270 -0.0058 0.2813 0.03 0.85 222 0.4332 0.2497 0.0312