CLAS physics database search results Measurement E151M3502 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 258 -0.0978 0.2527 0.0301 0.85 270 0.1303 0.266 0.0301 0.95 258 0.0952 0.2719 0.0301