Fully coupled-channel study of K− pp resonance in a chiral SU(3)-based Kbar N potential

Nuclear systems with antikaons, so-called kaonic nuclei, have been a longstanding issue in strange nuclear physics and hadron physics, because they might have exotic nature; In particular, they could be a doorway to the dense matter due to the strong attraction between antikaon and nucleon. Among kaonic nuclei, the three-body system composed of two protons and a single K− meson, K− pp, is the most essential. In this article, we will report on the recent situation of K− pp studies in both theoretical and experimental sides. Afterwards, we will explain our latest study of the K− pp with a fully coupled-channel complex scaling method (Full ccCSM) using a chiral SU(3)-based KN(-πY) potential. In Full ccCSM, the K− pp is completely treated as a resonant state of a KNN-πΣN-πΛN coupled-channel system. The energy dependence involved in the chiral potential is handled with a self-consistent calculation in which two extreme ansatzes are examined: field picture and particle picture. With our chiral SU(3)-based potential constrained by the precise data of kaonic hydrogen atom (SIDDHARTA experiment), the K− pp resonance is obtained as a shallowly bound state measured from the KNN threshold with a narrow width, if the field picture is employed in the calculation: the binding energy is 14 – 28 MeV and the half value of the mesonic decay width is 8 – 15 MeV. On the other hand, if the particle picture is employed, it is found that the binding energy could be as large as about 50 MeV, even though such a chiral potential is used. Based on these results of Full ccCSM calculation, we have discussed on the possibility for kaonic nuclei to form a dense matter and on the latest experimental result reported by J-PARC E15 collaboration.