CLAS physics database search results Measurement E151M2693 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 114 -0.0442 0.2691 0.03 0.65 282 0.2496 0.3403 0.0304 0.85 270 0.5888 0.3466 0.0322