CLAS physics database search results Measurement E151M3160 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 210 -0.1845 0.2458 0.0302 0.85 222 0.3064 0.2271 0.0306