CLAS physics database search results Measurement E151M3359 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 90 -0.0456 0.2617 0.03 0.85 222 -0.0644 0.2486 0.03 0.85 234 -0.3404 0.1567 0.0316