KN scattering amplitude revisited in a chiral unitary approach and a possible broad resonance in S=+1 channel

Abstract

We revisit the $KN$ scattering amplitude in order to investigate the possibility for the existence of a broad resonance in the $I=0$ $KN$ channel around the energy of 1617 MeV with 305 MeV width. We use the chiral unitary model to describe the $KN$ scattering amplitudes and determine the model parameters so as to reproduce the differential cross sections of the $K^{+}N$ scatterings and the $I=0$ and 1 total cross sections up to $p_{lab} = 800$ MeV/c, from which inelastic contributions start to be significant. Performing analytic continuation of the determined amplitude to the complex energy plane, we find a pole for a broad resonance state. We point out that the rapid increase appearing in the $I=0$ total cross section around $p_{lab}=500$ MeV/c is a hint of the possible broad resonance of strangeness $S=+1$.