On the structure in the $\Lambda N$ cross section at the $\Sigma N$ threshold

TL;DR

This paper investigates the complex threshold phenomena in hyperon-nucleon interactions, analyzing the $ m \Lambda p$ cross section near the $ m \Sigma N$ threshold, identifying poles, and providing evidence for a strangeness $S=-1$ dibaryon.

Contribution

It offers a detailed analysis of the $ m \\Lambda p$ cross section structure at the $ m \\Sigma N$ threshold using hyperon-nucleon potentials and identifies a possible strangeness $S=-1$ dibaryon state.

Findings

Identification of poles near the $ m \\Sigma N$ threshold.

Evidence for a strangeness $S=-1$ dibaryon.

Predictions for $ m \\Sigma^-p$ atomic level shifts and widths.

Abstract

The complexity of threshold phenomena is exemplified on a prominent and long-known case - the structure in the $\Lambda p$ cross section (invariant mass spectrum) at the opening of the $\Sigma N$ channel. The mass splitting between the $\Sigma$ baryons together with the angular momentum coupling in the $^3S_1$-$^3D_1$ partial wave imply that, in principle, up to six channels are involved. Utilizing hyperon-nucleon potentials that provide an excellent description of the available low-energy $\Lambda p$ and $\Sigma N$ scattering data, the shape of the resulting $\Lambda p$ cross section is discussed and the poles near the $\Sigma N$ threshold are determined. Evidence for a strangeness $S=-1$ dibaryon is provided, in the form of a deuteron-like (unstable) $\Sigma N$ bound state. Predictions for level shifts and widths of $\Sigma^-p$ atomic states are given.