CLAS physics database search results Measurement E151M3110 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 246 -0.2715 0.2794 0.0305 0.85 78 -0.0789 0.2673 0.03 0.85 90 -0.1131 0.2725 0.0301 0.85 246 -0.2895 0.2332 0.0306