CLAS physics database search results Measurement E151M2233 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 78 -0.3103 0.7914 0.0375 0.75 90 -0.2262 0.9417 0.0342 0.75 258 -0.7442 0.8303 0.0617 0.75 306 -0.5464 0.7932 0.0497 0.85 270 0.5266 0.8527 0.0486 0.85 282 -0.2398 0.8385 0.0347