CLAS physics database search results Measurement E151M3636 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 90 -0.1483 0.2575 0.0301 0.85 222 0.127 0.2758 0.0301 0.95 198 0.1044 0.2821 0.0301