CLAS physics database search results Measurement E151M2911 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.95 114 -0.0042 0.2725 0.03 0.95 126 -0.3842 0.2694 0.031 0.95 138 -0.0446 0.2637 0.03