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

TL;DR

This study confirms the Lambda(1405) resonance at approximately 1405.5 MeV/c2 through analysis of K- absorption in helium isotopes, challenging recent higher-mass predictions and proposing further tests with 3He.

Contribution

It provides experimental confirmation of the Lambda(1405) resonance mass and width, using a coupled-channel analysis of old bubble chamber data, and refutes recent chiral-SU(3) model predictions.

Findings

Lambda(1405) mass confirmed at ~1405.5 MeV/c2

Width of the resonance determined as ~26 MeV

Results challenge recent chiral-SU(3) predictions

Abstract

The Sigma-pi 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 (Gamma). A chi2 analysis of old 4He bubble chamber data shows a dominance of the s-orbit absorption, and yielded M = 1405.5 ^(+1.4)_(-1) MeV/c2 and Gamma = 26 ^(+4)_(-3) MeV, where a possible population of Sigma0(1385) and also a small p-orbit capture contribution are taken into account. This result confirms the Lambda(1405) ansatz, whereas recent chiral-SU(3) predictions (M ~ 1420 MeV/c2) are excluded. A more stringent test by using a 3He target is proposed .