CLAS physics database search results Measurement E151M3313 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.95 234 -0.0104 0.2579 0.03 0.85 114 -0.2741 0.2312 0.0305