CLAS physics database search results Measurement E151M2974 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 234 0.0482 0.2733 0.03 0.75 246 0.0051 0.2394 0.03 0.85 246 0.0899 0.2831 0.0301