CLAS physics database search results Measurement E151M3657 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 186 -0.3792 0.2521 0.0309 0.85 114 0.431 0.205 0.0312 0.85 126 0.1675 0.2643 0.0302 0.85 198 0.2326 0.2586 0.0304