Photoproduction ofK+Mesons and Polarization ofΛ0Hyperons in the 1-GeV Range

Polarization of $\Lambda$ hyperons and differential cross sections for the reaction $\gamma +p\to K^{+}+\Lambda$ were measured at the $K^{+}$-meson center-of-mass angles around 45°, 70°, and 90° 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 $\Lambda$ was determined by measuring the up-down asymmetry of protons in the decay $\Lambda \to p{\pi }^{-}$ with respect to the production plane. The results show a dominant $sin\theta _K^{}{}_{}{}^{*}$ 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.