CLAS physics database search results Measurement E151M3272 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.75 90 -0.1117 0.2523 0.0301 0.75 246 0.3178 0.2336 0.0307 0.85 282 -0.0543 0.2528 0.03