CLAS physics database search results Measurement E151M2753 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.65 234 -0.2315 0.2427 0.0304 0.75 222 0.0369 0.2808 0.03 0.75 246 0.0473 0.2799 0.03