CLAS physics database search results Measurement E151M1203 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 102 0.7695 1.0149 0.0637 0.85 222 -0.6508 0.8306 0.0562