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 Sigma pi invariant-mass spectra in the resonant capture of K- at rest in He-4, He-3 and d ire calculated by a coupled-channel procedure for a K-p quasi-bound state of ail arbitrary chosen mass (M) and width (Gamma) A X-2 analysis of old 4He bubble chamber data shows a dominance of the s-orbit absorption, and yielded M = 1405 5(-1)(+1 4) MeV/c(2) and Gamma = 24(-3)(+4) Mev, where a possible Population of Sigma(0)(1385) and also a small p-orbit capture contribution are taken into account This result confirms the A(1405) ansatz, whereas recent chiral-SU(3) predictions (M - 1420 MeV/c2) are excluded A more stringent lest by using a He-3 target is proposed (C) 2010 Elsevier BV All rights reserved.