CLAS physics database search results Measurement E151M1683 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.55 222 -0.5684 1.0172 0.0454 0.65 222 -1.6507 0.8668 0.1034 0.55 234 0.2794 1.2141 0.0341 0.75 222 0.0714 1.1316 0.0303 0.75 234 -2.215 0.7443 0.1322 0.85 222 0.6516 1.2373 0.0483