ΛPolarization at 90° inK+ΛPhotoproduction

The $\Lambda$ polarization and the differential cross section for the reaction $\gamma +p\to K^{+}+\Lambda$ have been measured, using the Caltech synchrotron, at 90° in the c.m. system and at laboratory photon energies of 1100, 1200, and 1300 MeV. Protons from the asymmetric decay of the $\Lambda$ were detected by counters placed above and below the production plane. Kaons were identified by their behavior in a thick range telescope. Polarization results were $P_{\Lambda }=+0.34\mathrm{}\pm 0.09$ at 1100 MeV, $+0.30\mathrm{}\pm 0.07$ at 1200 MeV, and $+0.08\mathrm{}\pm 0.07$ at 1300 MeV, where $P_{\Lambda }$ was measured in the ${\hat{p}}_{\gamma }\times {\hat{p}}_{\Lambda }$ direction. The differential cross section was constant with energy at 0.14±0.01 μb/sr. Although the apparent bump in the polarization at 90° at a total energy of $\approx 1700$ MeV adds support to models which invoke a resonance here, no really new conclusions can be reached.