Polarization in hyperon photo- and electro-production

Multiple polarization observables must be measured to access the amplitude structure of pseudoscalar meson photoproduction off the proton. The hyperon-producing reactions are especially attractive to study, since the weak decays allow straightforward measurement of the induced and recoil polarization observables. In this paper we emphasize gamma + p -> K+ + Lambda , discussing recent measurements of C-x, C-z, and P for this reaction. An empirical constraint on the helicity amplitudes is obtained. A simplified model involving spin-flip and spin-non-flip amplitudes is presented. Finally, a semi-classical model of how the polarization may arise is presented.