CLAS physics database search results Measurement E151M346 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.85 126 1.3764 0.6556 0.0904 0.85 258 -0.4454 0.8179 0.0402 0.95 282 0.5658 1.0206 0.0454 0.85 270 -0.6262 0.6217 0.049