CLAS physics database search results Measurement E151M2790 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 126 -0.55 0.2397 0.032 0.85 258 0.4378 0.3436 0.0313 0.95 282 0.1013 0.4188 0.0301 0.85 270 0.3203 0.2428 0.0307