CLAS physics database search results Measurement E151M1928 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 210 -2.0698 2.0698 0.129 0.75 294 0.9824 0.6786 0.0667 0.85 222 0.0385 0.6569 0.0301 0.85 234 0.04 0.6082 0.0301 0.85 246 0.6304 0.6074 0.0486