$K^+ \Lambda$ Photoproduction in the $u$-channel

Photoproduction of the $\gamma p \to K^+ \Lambda$ reaction at backward center-of-mass angles has been measured by detecting the $\Lambda$ at forward angles using the LEPS spectrometer. The $K^+$ was identified by the missing mass technique. The data cover center-of-mass angles beyond 145$^\circ$ for six photon energy bins between 1.5 and 2.4 GeV. The results are sensitive to $u$-channel diagrams, especially at the most backward angles, where a neutral hyperon is propagated between the kaon and photon verticies. These data provide the first stringent test of $u$-channel diagrams in hyperon photoproduction. If available, calculations using a full coupled-channels model will be compared with photon energy- dependence of the data.