CLAS physics database search results Measurement E151M2403 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.85 90 1.0594 1.0349 0.0825 0.85 210 0.8695 1.098 0.0698 0.95 198 0.1832 1.0359 0.0328 0.95 222 -0.8143 0.9858 0.0662 0.95 246 -0.3289 0.9463 0.0383