CLAS physics database search results Measurement E151M2437 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.75 270 1.2502 0.9816 0.0955 0.85 102 1.4372 0.8121 0.1084 0.85 114 -0.8202 0.9495 0.0666 0.85 126 -1.001 1.0668 0.0785 0.85 186 1.6623 0.9572 0.1242 0.85 198 -0.7593 1.091 0.0627