Single-pole nature of Λ(1405) and structure of K−pp

We have studied the structure of K−pp by solving this system in a variational treatment, starting from Ansatz that Λ(1405) is a K−p quasi-bound state, Λ∗ with mass 1405 MeV/c2. The structure of K−pp reveals a molecular feature, namely, the K− in an “atomic center”, Λ∗, plays a key role in producing strong covalent bonding with the other proton. Deeply bound nuclear systems are formed by this “super-strong” nuclear force due to migrating real bosons, , a la Heitler-London-Heisenberg, which overcompensates the stiff nuclear incompressibility. Theoretical background of the Λ(1405) Ansatz is discussed in connection with the double-pole picture of Λ(1405) based on chiral SU(3) dynamics. Detailed analysis reveals single-pole nature of the observable Λ(1405). There are two kinds of Σπ invariant masses experimentally observable, the usual T22 invariant mass and the conversion T21 invariant mass. It is of virtual importance to determine whether the Λ∗ mass is 1405 MeV or 1420 MeV. The T21 invariant mass from K− absorption at rest in deuteron can provide decisive information about this Λ∗ mass problem.