CLAS physics database search results Measurement E151M2461 EG4 Xiaochao Zheng 2016 cos(theta_pi+) phi(pi+) A_LU Stat. error Syst. error degrees 0.45 282 -0.0024 0.2088 0.03 0.55 282 -0.0662 0.2225 0.03 0.65 282 0.2683 0.2447 0.0305 0.95 162 -0.0791 0.2319 0.03