Variational calculation of the ppK^- system based on chiral SU(3) dynamics

The ppK^- system, as a prototype for possible quasibound K̅ nuclei, is investigated using a variational approach. Several versions of energy-dependent effective K̅ N interactions derived from chiral SU(3) dynamics are employed as input, together with a realistic NN potential (Av18). Taking into account theoretical uncertainties in the extrapolations below the K̅ N threshold, we find that the antikaonic dibaryon ppK^- is not deeply bound. With the driving s-wave K̅ N interaction the resulting total binding energy is B(ppK^-)=20±3 MeV and the mesonic decay width involving K̅ N→πY is expected to be in the range 40–70 MeV. Properties of this quasibound ppK^- system (such as density distributions of nucleons and antikaon) are discussed. The Λ(1405), as an I=0 quasibound state of K̅ and a nucleon, appears to survive in the ppK^- cluster. Estimates are given for the influence of p-wave K̅ N interactions and for the width from two-nucleon absorption (K̅ NN→YN) processes. With inclusion of these effects and dispersive corrections from absorption, the ppK^- binding energy is expected to be in the range 20–40 MeV, whereas the total decay width can reach 100 MeV but with large theoretical uncertainties.