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

Abstract

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.