CLAS physics database search results Measurement E151M1566 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 234 -0.1434 1.2355 0.0311 0.75 246 1.0733 1.2196 0.0692 0.85 258 0.7866 0.9797 0.0547 0.65 246 1.633 0.9202 0.1024 0.75 246 1.075 0.9472 0.0711 0.85 258 -0.3139 0.8446 0.0354 0.85 270 -0.0944 0.9244 0.0305 0.95 258 0.0435 0.6961 0.0301