CLAS physics database search results Measurement E151M1927 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 210 -0.4841 0.6786 0.042 0.75 234 -1.1263 0.6036 0.0746 0.85 222 -0.1621 0.7076 0.0316 0.85 246 -0.9058 0.7061 0.0626