Physical Review Letters
We present new data for the polarization observables of the final state proton in the H-1((gamma) over right arrow, (p) over right arrow)pi(0) reaction. These data can be used to test predictions based on hadron helicity conservation and perturbative QCD. These data have both small statistical and systematic uncertainties and were obtained with beam energies between 1.8 and 5.6 GeV and for pi(0) scattering angles larger than 75 degrees in the center-of-mass frame. The data extend the polarization measurements database for neutral pion photoproduction up to E-gamma = 5.6 GeV. The results show a nonzero induced polarization above the resonance region. The polarization transfer components vary rapidly with the photon energy and pi(0) scattering angle in the center-of-mass frame. This indicates that hadron helicity conservation does not hold and that the perturbative QCD limit is still not reached in the energy regime of this experiment.
Luo, W., Brash, E. J., Gilman, R., Jones, M. K., Meziane, M., Pentchev, L., ... & Ahmidouch, A. (2012). Polarization Components in π 0 Photoproduction at Photon Energies up to 5.6 GeV. Physical review letters, 108(22), 222004.