CLAS physics database search results Measurement E151M3170 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 114 -0.0941 0.2589 0.0301 0.85 222 -0.2827 0.2566 0.0305