CLAS physics database search results Measurement E151M1945 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 78 -1.5862 0.7743 0.1007 0.75 210 -2.1001 0.6732 0.1307 0.75 258 1.1323 0.8671 0.0749 0.75 270 0.0195 0.8382 0.03 0.75 282 -0.8765 0.8086 0.061