CLAS physics database search results Measurement E151M1903 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 246 0.0664 0.86 0.0303 0.85 210 -0.4566 0.9036 0.0408 0.85 234 0.0246 0.8125 0.03 0.95 102 0.7979 0.7724 0.0569