Resonant formation of Lambda(1405) by stopped-K- absorption in deuteron

TL;DR

This paper proposes a method to measure the Sigma-pi invariant-mass spectrum in stopped-K- absorption in deuteron to clarify the nature and position of the Lambda(1405) resonance, distinguishing it from quasi-free background.

Contribution

It introduces a novel spectral analysis technique using a deviation spectrum to isolate the Lambda(1405) resonance in stopped-K- absorption experiments.

Findings

The spectrum features a narrow quasi-free component with an upper edge at 1430 MeV/c^2.

A significant high-momentum tail indicates potential resonant formation of Lambda(1405).

The deviation spectrum effectively isolates the resonant signal from non-resonant background.

Abstract

To solve the current debate on the position of the quasi-bound K^-p state, namely, "Lambda(1405) or Lambda*(1420)", we propose to measure the T_{21} = T_{Sigma-pi \leftarrow Kbar-N} Sigma-pi invariant-mass spectrum in stopped-K- absorption in deuteron, since the spectrum, reflecting the soft and hard deuteron momentum distribution, is expected to have a narrow quasi-free component with an upper edge of M = 1430 MeV/c^2, followed by a significant "high-momentum" tail toward the lower mass region, where a resonant formation of Lambda(1405) of any mass and width in a wide range is revealed. We introduce a "deviation" spectrum as defined by DEV = OBS (observed or calculated) / QF (non-resonant quasi-free), in which the resonant component can be seen as an isolated peak free from the QF shape.