CLAS physics database search results Measurement E151M2959 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.65 78 -0.2451 0.2494 0.0304 0.75 102 0.2479 0.2743 0.0304 0.75 294 -0.0102 0.2734 0.03 0.85 102 -0.1792 0.277 0.0302