CLAS physics database search results Measurement E151M787 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_UL Stat. error Syst. error degrees 0.75 114 -0.1326 0.6239 0.0312 0.75 258 0.3729 0.5288 0.0615 0.85 270 -0.4889 0.4848 0.0454 0.85 294 -0.7112 0.497 0.0555