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    Cross sections for the reactions $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}$ and $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{0}$ have been measured at squared four-momentum transfer ($\ensuremath{-}t$) from 0.005 to 2 ${\mathrm{GeV}}^{2}$, at photon energies 5, 8, 11, and 16 GeV. For $\ensuremath{-}t>0.2$ ${\mathrm{GeV}}^{2}$ each of the ${K}^{+}$ cross sections is about ⅓ of the ${\ensuremath{\pi}}^{+}n$ photoproduction cross section, having nearly the same energy and momentum-transfer dependence. The ${K}^{+}$ cross sections fall off at small $|t|$, however, in contrast to the sharp forward spike seen in ${\ensuremath{\pi}}^{+}n$; this leads to a disagreement with an SU(3) prediction for $\ensuremath{-}t<0.1$ ${\mathrm{GeV}}^{2}$. The ratio of ${K}^{+}{\ensuremath{\Sigma}}^{0}$ to ${K}^{+}\ensuremath{\Lambda}$ cross sections is typically between 0.5 and 1.0.
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    Polarization of $\ensuremath{\Lambda}$ hyperons and differential cross sections for the reaction $\ensuremath{\gamma}+p\ensuremath{\rightarrow}{K}^{+}+\ensuremath{\Lambda}$ were measured at the ${K}^{+}$-meson center-of-mass angles around 45\ifmmode^\circ\else\textdegree\fi{}, 70\ifmmode^\circ\else\textdegree\fi{}, and 90\ifmmode^\circ\else\textdegree\fi{} for the incident photon energies of 1054, 1100, and 1160 MeV. The ${K}^{+}$ mesons were detected with a magnetic spectrometer and a velocity-selection system based on the energy loss and the time of flight. The polarization of $\ensuremath{\Lambda}$ was determined by measuring the up-down asymmetry of protons in the decay $\ensuremath{\Lambda}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{\ensuremath{-}}$ with respect to the production plane. The results show a dominant $sin\ensuremath{\theta}_{K}^{}{}_{}{}^{*}$ dependence of the polarization at the region of the third resonance and are consistent with a contribution of the ${P}_{11}$ resonance with a mass of about 1700 MeV.
    Citations (23)