Helicity Asymmetry Measurement for pi0 Photoproduction with FROST
Open AccessThis thesis reports on the first helicity asymmetry measurement for single neutral pion photoproduction using the CLAS detector in Hall B at the Thomas Jefferson National Accelerator Facility (JLab).This measurement used longitudinally polarized protons and circularly polarized photons at energies between 350 MeV and 2400 MeV. The experimental results are compared to three available model calculations.The target used in this experiment was butanol (C4H9OH). The protons in the target were polarized via the Dynamical Nuclear Polarization (DNP) technique. During the experiment, the target polarization was kept between 78 % and 92 %. The relaxation time of the target polarization was about 2,000 hours during the experiment. The photon beam was produced by the photon tagging system in Hall B.Two different electron beam energies, 1,465 GeV and 2.478 GeV, with a longitudinal electron polarization between 80 ∼ 87 % were used to produce the circularly polarized photon beam on a thin gold radiator.An additional carbon target, positioned downstream of the butanol target, was used to subtract the background from bound-nucleon reactions.The helicity asymmetry E was measured with high statistics of about 12 Million events using the missing mass technique.The result is in good agreement with model calculations up to Ephoton = 1.35 GeV.However, significant deviations are observed at the backward pion scattering angles, -0.75 ≤ cos theta ≤ 0.The helicity asymmetry is very sensitive to various dynamical reaction effects, such as channel coupling and final state interactions. Therefore, the new data will help to constrain the parameters of the theoretical models.
- All rights reserved
Notice to Authors
If you are the author of this work and you have any questions about the information on this page, please use the Contact form to get in touch with us.