CLAS physics database search results Measurement E151M2504 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.65 234 0.3646 0.2156 0.0309 0.65 246 -0.2432 0.1888 0.0304 0.75 246 -0.2591 0.234 0.0304