CLAS physics database search results Measurement E151M2168 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.45 282 -0.2291 0.7599 0.0343 0.55 282 0.1697 0.6873 0.0324 0.55 294 0.7784 0.7075 0.0639 0.75 90 0.7406 0.7543 0.0615 0.75 270 -1.7924 0.642 0.1334 0.75 294 -0.2622 0.7445 0.0355 0.85 66 -0.2435 0.7925 0.0348 0.85 78 1.0371 0.6984 0.081