Cross sections for the reactions $\gamma p\to K^{+}\Lambda$ and $\gamma p\to K^{+}{\Sigma }^0$ have been measured at squared four-momentum transfer ($-t$) from 0.005 to 2 ${\mathrm{GeV}}^2$, at photon energies 5, 8, 11, and 16 GeV. For $-t>\mathrm{}0.2\mathrm{}$ ${\mathrm{GeV}}^2$ each of the $K^{+}$ cross sections is about ⅓ of the ${\pi }^{+}n$ photoproduction cross section, having nearly the same energy and momentum-transfer dependence. The $K^{+}$ cross sections fall off at small $\mathrm{}\left|t\right|\mathrm{}$, however, in contrast to the sharp forward spike seen in ${\pi }^{+}n$; this leads to a disagreement with an SU(3) prediction for $-t<\mathrm{}0.1\mathrm{}$ ${\mathrm{GeV}}^2$. The ratio of $K^{+}{\Sigma }^0$ to $K^{+}\Lambda$ cross sections is typically between 0.5 and 1.0.

• Received 1 April 1969

DOI:https://doi.org/10.1103/PhysRevLett.22.1131