Evidence for the Jp=1/2+ narrow state at 1650 MeV in the photoproduction of KΛ

We have investigated the existence of the Jp=1/2+ narrow resonance predicted by the chiral soliton model by utilizing the kaon photoproduction process γ+p→K++Λ. For this purpose we have constructed two phenomenological models based on our previous effective Lagrangian model, which are able to describe kaon photoproduction from threshold up to W=1730 MeV. By varying the mass (width) of an inserted P11 resonance from 1620 to 1730 MeV (0.1 to 1 MeV and 1 to 10 MeV) a number of fits have been performed in order to search for the resonance mass. Our result indicates that the most promising candidate mass (width) of this resonance is 1650 MeV (5 MeV). Although our calculation does not exclude the possibility of narrow resonances with masses of 1680, 1700, and 1720 MeV, the mass of 1650 MeV is obtained for all phenomenological models used in this investigation. Variations of the resonance width and KΛ branching ratio are found to have a mild effect on the χ2. The possibility that the obtained result originates from other resonance states is also discussed.