CLAS physics database search results Measurement E151M2153 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 270 -0.7553 0.8057 0.0756 0.85 102 0.6543 1.1717 0.0672 0.85 114 0.3569 1.0014 0.0445 0.65 138 -0.4117 0.7367 0.0402 0.65 210 -0.4482 0.7842 0.0418 0.85 102 -1.5398 0.666 0.1046