CLAS physics database search results Measurement E151M2904 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 246 -0.4993 0.3408 0.0316 0.85 222 0.5304 0.3247 0.0318 0.65 234 0.1472 0.2826 0.0301 0.75 234 -0.1495 0.2737 0.0301