CLAS physics database search results Measurement E151M252 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.65 246 -0.3404 0.3518 0.0555 0.75 234 1.2093 0.5151 0.0807 0.65 258 -0.3408 0.7343 0.0363 0.75 246 -0.7595 0.523 0.0547 0.75 258 -0.6286 0.603 0.0483 0.85 246 -0.1596 0.7316 0.0315