CLAS physics database search results Measurement E151M1283 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LL Stat. error Syst. error degrees 0.65 246 -0.1812 0.6842 0.0363 0.75 234 0.7453 0.825 0.0892 0.75 246 0.2396 0.6945 0.0404 0.75 258 0.5091 0.7045 0.0648