CLAS physics database search results Measurement E151M2844 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 138 -0.1554 0.2538 0.0302 0.85 246 0.1959 0.2684 0.0303 0.85 270 -0.3468 0.2824 0.0308