Helicity Asymmetry E Measurement for single π0 Photoproduction with a Frozen Spin Target

The helicity asymmetry for single neutral pion photoproduction was measured using the CLAS detecter in Hall B at the Thomas Jefferson National Accelerator Facility. This measurement used longitudinally polarized protons and circularly polarized photons with photon energies between 0.35 GeV to 2.4 GeV. The target was frozen-spin butanol (C4H9OH) target, polarized at about 85%. The helicity asymmetry E for gamma p -> p pi(0) was measured with missing-mass technique at the high statistics of about 12 x 10(6) events. The experimental results are compared to three available theoretical predictions, SAID, MAID, and EBAC. The preliminary results are in good agreement with the model calculations at low E-gamma energy bins. However, a significant deviation is observed at high energy bins. Therefore, the new data will help to constrain the parameters of the theoretical models.