CLAS physics database search results Measurement E151M3603 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 66 -0.0077 0.2754 0.03 0.85 246 -0.0182 0.2275 0.03 0.95 270 0.1922 0.2819 0.0302