CLAS physics database search results Measurement E151M3258 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.85 270 -0.1096 0.2499 0.0301 0.75 270 0.3477 0.2381 0.0308 0.85 258 -0.0306 0.2569 0.03