CLAS physics database search results Measurement E151M668 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.65 222 0.2359 0.8051 0.0333 0.75 198 0.2101 0.8103 0.0326 0.75 210 0.2373 0.8063 0.0333 0.85 126 -0.4372 0.7271 0.0402 0.85 138 -1.0057 0.6306 0.0684 0.85 222 1.0185 0.691 0.0691