CLAS physics database search results Measurement E151M17 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Data errors Systematic errors degrees 0.45 282 -0.1327 0.4072 0.0336 0.55 282 -0.7796 0.3649 0.0936 0.65 282 -0.2315 0.4869 0.0399 0.95 162 -0.4289 0.3395 0.0573