CLAS physics database search results Measurement E151M471 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.75 270 0.4897 0.5336 0.0424 0.95 102 -0.0284 0.4597 0.0301 0.95 114 0.5499 0.5467 0.0451