CLAS physics database search results Measurement E151M1984 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.85 258 0.1586 0.6678 0.0317 0.85 270 -0.1229 0.6292 0.031 0.75 282 1.8498 1.5755 0.1726 0.85 90 4.6034 1.9075 0.4241 0.85 306 0.7898 1.8888 0.0785