CLAS physics database search results Measurement E151M1022 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 270 -0.4471 0.6452 0.0444 0.85 306 -0.4265 0.6282 0.0433 0.85 318 -0.6086 0.6202 0.0537