Is there an eta-3He quasi--bound state ?

TL;DR

This paper investigates the rapid change in the eta-3He interaction near threshold, suggesting the possible existence of a quasi-bound or virtual eta-3He state based on cross section and phase variation analysis.

Contribution

It provides evidence for a quasi-bound eta-3He state by analyzing the phase variation of the s-wave amplitude near threshold.

Findings

Rapid fall of s-wave amplitude magnitude near threshold

Strong phase variation consistent with a quasi-bound state

Recommendations for further spin-dependent measurements

Abstract

The observed variation of the total cross section for the dp -> 3He eta reaction near threshold means that the magnitude of the s--wave amplitude falls very rapidly with the eta centre--of--mass momentum. It is shown here that recent measurements of the momentum dependence of the angular distribution imply a strong variation also in the phase of this amplitude. Such a behaviour is that expected from a quasi--bound or virtual eta-3He state. The interpretation can be investigated further through measurements of the deuteron or proton analysing powers and/or spin--correlations.