CLAS physics database search results Measurement E151M2696 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.65 246 0.0269 0.2223 0.03 0.75 234 -0.4144 0.2726 0.0311 0.65 258 -0.9528 0.1404 0.0355 0.75 246 -0.3811 0.3421 0.031 0.75 258 -0.2812 0.3847 0.0305 0.85 246 0.1431 0.4096 0.0301