CLAS physics database search results Measurement E151M3138 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.65 294 -0.2756 0.272 0.0305 0.85 102 -0.0992 0.2426 0.0301 0.85 246 0.0267 0.2496 0.03 0.85 258 -0.3627 0.2544 0.0309