CLAS physics database search results Measurement E151M3646 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 90 -0.4677 0.2311 0.0314 0.85 186 -0.3085 0.2519 0.0306 0.85 210 0.1043 0.2479 0.0301 0.95 222 -0.2137 0.2635 0.0303