CLAS physics database search results Measurement E151M2426 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 114 0.9994 0.9979 0.0784 0.75 210 -0.5897 0.9763 0.0522 0.75 282 -1.2046 0.8378 0.0924 0.85 126 -1.3879 1.0249 0.105 0.85 186 -1.7135 0.8608 0.1278 0.85 198 -0.834 0.8728 0.0675 0.85 270 -1.2793 0.833 0.0975