CLAS physics database search results Measurement E151M2126 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 114 -1.1734 0.8569 0.082 0.75 210 -2.1443 0.8258 0.1427 0.85 210 0.071 1.0279 0.0304 0.85 246 0.2384 1.0027 0.0338