CLAS physics database search results Measurement E151M2484 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.55 258 -0.446 0.2201 0.0313 0.55 270 -0.2367 0.2408 0.0304 0.65 246 -0.1046 0.2498 0.0301 0.75 246 0.1801 0.245 0.0302