CLAS physics database search results Measurement E151M1421 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 258 -0.2866 0.7341 0.0343 0.65 270 -0.397 0.6978 0.0379 0.85 162 -0.29 0.7168 0.0344 0.85 198 -0.7091 0.6999 0.051 0.55 270 -0.5832 0.5967 0.0461 0.75 174 -0.1241 0.5488 0.0309 0.75 258 -0.0705 0.6062 0.0303 0.85 186 -0.0598 0.5572 0.0302