CLAS physics database search results Measurement E151M3361 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 90 -0.2784 0.2487 0.0305 0.85 210 -0.32 0.2198 0.0307