Are hyperon resonances required in the elementary $K^+\Lambda$ photoproduction?

We have investigated the role of hyperon resonances in the kaon photoproduction process, $\gamma p\to K^+\Lambda$, by using a covariant isobar model. To this end, new experimental data are used in the fitting process, whereas the old SAPHIR 1998 data are also used for comparison. The result indicates that the $\Lambda(1600)P_{01}$ and $\Lambda(1810)P_{01}$ hyperon resonances can significantly reduce the $\chi^2$ and, simultaneously, can increase the hadronic form factor cut-off in the background terms. This finding is different from the result of the previous studies, which showed that the $\Lambda(1800)S_{01}$ was important for this purpose, instead of the $\Lambda(1600)P_{01}$.