Experimental confirmation of the Λ(1405) Ansatz from resonant formation of a K−p quasi-bound state in K− absorption by 3He and 4He

The Σπ invariant-mass spectra in the resonant capture of K− at rest in 4He, 3He and d are calculated by a coupled-channel procedure for a K−p quasi-bound state of an arbitrary chosen mass (M) and width (Γ). A χ2 analysis of old 4He bubble chamber data shows a dominance of the s-orbit absorption, and yielded and , where a possible population of Σ0(1385) and also a small p-orbit capture contribution are taken into account. It is pointed out that the target of d is even more interesting; we have proposed that an experiment with d target should determine the mass and width of Λ(1405).