CLAS physics database search results Measurement E151M1182 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 234 -0.4737 0.8593 0.0458 0.95 210 1.6528 1.0216 0.1245