CLAS physics database search results Measurement E151M1857 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 114 -0.2218 0.921 0.0329 0.75 102 1.6742 0.8092 0.1058 0.75 246 0.5865 0.8505 0.0465 0.75 258 -1.4676 0.7726 0.0939 0.85 234 1.1711 0.8943 0.077 0.85 246 -0.0245 0.7369 0.03 0.85 258 -0.2586 0.7518 0.0338 0.95 78 0.5617 0.8366 0.0454 0.95 258 0.5477 0.7939 0.0447 0.95 270 -0.3994 0.7501 0.0385 0.95 282 0.1818 0.6512 0.032 0.95 294 0.0259 0.7656 0.03