CLAS physics database search results Measurement E151M1692 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 282 -0.6949 0.5205 0.0517 0.75 270 0.4436 0.5681 0.0403 0.95 114 -0.6716 0.5074 0.0506 0.95 126 0.1967 0.484 0.0323 0.95 138 0.0858 0.5801 0.0304