CLAS physics database search results Measurement E151M2392 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.85 198 -0.1446 1.0965 0.0318 0.85 234 0.3001 0.9744 0.0371 0.95 198 0.4602 0.9718 0.0449 0.95 210 -0.4724 1.0082 0.0455 0.95 222 0.3895 0.9872 0.0412 0.95 234 1.2291 0.9465 0.094