CLAS physics database search results Measurement E151M2547 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.55 246 -0.6065 0.1751 0.0324 0.65 234 0.0248 0.2444 0.03 0.65 246 -0.1328 0.2534 0.0301 0.75 246 0.1499 0.2297 0.0301