CLAS physics database search results Measurement E151M3162 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 234 0.2894 0.2593 0.0306 0.75 282 -0.2912 0.2554 0.0306 0.85 222 0.2353 0.2704 0.0304