CLAS physics database search results Measurement E151M3348 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 114 -0.0565 0.2597 0.03 0.75 210 0.2202 0.2488 0.0303 0.85 210 -0.2831 0.2283 0.0305 0.85 246 -0.2332 0.2547 0.0304