CLAS physics database search results Measurement E151M1058 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 258 0.2011 0.7145 0.0334 0.85 270 -0.0299 0.7069 0.0301 0.95 258 0.5443 0.7514 0.0498