Article

# Polarization Components in pi(0) Photoproduction at Photon Energies up to 5.6 GeV

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(Impact Factor: 7.51). 09/2011; 108(22). DOI: 10.1103/PhysRevLett.108.222004
Source: arXiv

ABSTRACT 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.

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Available from: John Robert Arrington, Jul 27, 2015
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##### Article: Measurement of the $^{1}H$($\vec{\gamma}$, $\vec{p}$)$\pi^{0}$ reaction using a novel nucleon spin polarimeter
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ABSTRACT: We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon, pioneering a novel polarimetry technique with wide application to future nuclear and hadronic physics experiments. The commissioning measurement of polarization transfer in the $^{1}H$($\vec{\gamma}$,$\vec{p}$)$\pi^{0}$ reaction in the range $0.4<E_{\gamma}<1.4$ GeV is highly selective regarding the basic parameterizations used in partial wave analyses to extract the nucleon excitation spectrum. The new data strongly favor the recently proposed Chew-Mandelstam formalism.