Polarization components in $\pi^{0}$ photoproduction at photon energies   up to 5.6 GeV
  We present new data for the polarization observables of the final state proton in the $^{1}H(\vec{\gamma},\vec{p})\pi^{0}$ reaction. These data can be used to test predictions based on hadron helicity conservation (HHC) and perturbative QCD (pQCD). 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$^{\circ}$ in center-of-mass (c.m.) frame. The data extend the polarization measurements data base for neutral pion photoproduction up to $E_{\gamma}=5.6 GeV$. The results show non-zero induced polarization above the resonance region. The polarization transfer components vary rapidly with the photon energy and $\pi^{0}$ scattering angle in c.m. frame. This indicates that HHC does not hold and that the pQCD limit is still not reached in the energy regime of this experiment. 
W. Luo, E. J. Brash, R. Gilman, M. K. Jones, M. Meziane, L. Pentchev,   C. F. Perdrisat, A. J. R. Puckett, V. Punjabi, F. R....
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