CLAS physics database search results Measurement E151M2414 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.85 90 -0.1431 1.0024 0.0317 0.85 222 -0.8916 1.0569 0.0713 0.95 198 -0.61 1.053 0.0534