Faddeev calculations of the $\bar{K}NN$ system with chirally-motivated $\bar{K}N$ interaction. II. The $K^- pp$ quasi-bound state

Abstract: New calculations of the quasi-bound state in the $K^- pp$ system using Faddeev-type equations in AGS form with coupled $\bar{K}NN$ and $\pi \Sigma N$ channels were performed. A chiral $\bar{K}N$ potential together with phenomenological models of $\bar{K}N$ interaction with one- and two-pole structure of the $\Lambda(1405)$ resonance were used. All three potentials reproduce experimental data on low-energy $K^- p$ scattering and kaonic hydrogen with the same level of accuracy. New method of calculating the subthreshold resonance position and width in a three-body system was proposed and used together with the direct search of the resonance pole. We obtained binding energy of the $K^-pp$ quasi-bound state $\sim 32$ MeV with the chirally motivated and $47 - 54$ MeV with the phenomenological $\bar{K}N$ potentials. The width is about $50$ MeV for the two-pole models of the interaction, while the one-pole potential gives $\sim 65$ MeV width. The question of using an energy dependent potential in few-body calculations is discussed in detail. It is shown that ``self-consistent'' variational calculations using such a potential are unable to produce a reasonable approximation to the exact result.