CLAS physics database search results Measurement E151M3153 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.55 210 -0.1212 0.2781 0.0301 0.75 66 -0.3635 0.2704 0.0309 0.85 126 -0.0382 0.2805 0.03