CLAS physics database search results Measurement E151M1640 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 222 -1.0803 1.0161 0.0714 0.85 234 -0.4499 0.9136 0.0403 0.65 246 0.1904 1.1508 0.032 0.65 258 -0.2243 1.1972 0.0327 0.75 246 0.7368 1.2026 0.0523