CLAS physics database search results Measurement E151M1681 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.55 234 -0.5199 1.393 0.0426 0.65 222 1.2101 1.1226 0.0765 0.75 222 0.6069 1.0933 0.0463 0.75 246 -1.1312 1.0191 0.0723