CLAS physics database search results Measurement E151M1587 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.55 222 -0.8098 0.9948 0.0558 0.55 234 0.2292 0.6831 0.0401 0.65 222 0.6761 0.7985 0.0504 0.65 234 -0.84 0.6715 0.064 0.75 222 -1.7775 0.7118 0.1076 0.75 234 -0.1013 0.8706 0.0306