CLAS physics database search results Measurement E151M1159 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.85 66 1.6804 1.025 0.1264 0.85 246 2.8258 2.8258 0.2087 0.95 270 -0.3931 0.7517 0.0415