CLAS physics database search results Measurement E151M2445 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.95 150 -0.1541 0.2401 0.0302 0.95 210 0.1822 0.2435 0.0302