CLAS physics database search results Measurement E151M3231 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 114 -0.0923 0.2569 0.0301 0.75 258 -0.0709 0.1702 0.0304 0.85 270 -0.0593 0.1706 0.03 0.85 294 0.2057 0.2365 0.0303