CLAS physics database search results Measurement E151M1666 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.55 222 -0.7839 0.9538 0.0557 0.75 234 -0.6346 0.8326 0.0484 0.85 222 0.2844 0.7342 0.0345 0.55 234 -2.2285 0.7728 0.133 0.65 234 -0.4541 1.024 0.04 0.75 234 -1.4402 0.9511 0.089 0.85 234 -1.8159 1.0869 0.1098 0.85 246 -0.2173 1.2653 0.0326