CLAS physics database search results Measurement E151M2901 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 222 -0.0577 0.2538 0.03 0.75 246 0.2232 0.2828 0.0303 0.65 234 0.3211 0.3574 0.0307 0.75 234 0.4355 0.3103 0.0312 0.85 222 0.7696 0.2101 0.0337