K ¯ + N → K + Ξ reaction and S = − 1 hyperon resonances

The K¯¯¯+N→K+Ξ reaction is studied for center-of-momentum energies ranging from threshold to 3 GeV in an effective Lagrangian approach that includes the hyperon s- and u-channel contributions as well as a phenomenological contact amplitude. The latter accounts for the rescattering term in the scattering equation and possible short-range dynamics not included explicitly in the model. Existing data are well reproduced and three above-the-threshold resonances were found to be required to describe the data, namely, the Λ(1890), Σ(2030), and Σ(2250). For the latter resonance we have assumed the spin-parity of JP=5/2− and a mass of 2265 MeV. The Σ(2030) resonance is crucial in achieving a good reproduction of not only the measured total and differential cross sections but also the recoil polarization asymmetry. More precise data are required before a more definitive statement can be made about the other two resonances, in particular, about the Σ(2250) resonance that is introduced to describe a small bump structure observed in the total cross section of K−+p→K++Ξ−. The present analysis also reveals a peculiar behavior of the total cross-section data in the threshold energy region in K−+p→K++Ξ−, where the P and D waves dominate instead of the usual S wave. Predictions for the target-recoil asymmetries of the K¯¯¯+N→K+Ξ reaction are also presented