Eta-Mesic Nucleus and COSY-GEM Data

TL;DR

This paper reanalyzes COSY-GEM experimental data on eta-mesic nuclei formation, comparing theoretical predictions with observed spectra, and suggests interference effects and attractive N*(1535)-nucleus interactions are key to understanding the results.

Contribution

It provides a new interpretation of experimental data by including interference effects and offers insights into the eta-mesic nucleus and N*(1535)-nucleus interaction.

Findings

Spectrum explained with interference effects

Interaction between N*(1535) and nucleus is attractive

Data supports existence of eta-mesic nuclei

Abstract

The experimental data of the COSY-GEM Collaboration for the recoil-free transfer reaction p (27Al, 3He) \pi - p' X, leading to the formation of bound state of eta (\eta) meson in 25Mg nucleus, is reanalyzed in this paper. In particular, predicted values of binding energy and half-width of the \eta -mesic nucleus 25Mg\eta, given by different theoretical approaches, are compared with the ones obtained from the experimental missing mass spectrum. It is found that the spectrum can be explained reasonably well if interference effect of another process, where \eta is not bound in 25Mg but is scattered by the nucleus and emerge as a pion, is taken into account. The data also indicate that the interaction between N*(1535) and a nucleus is attractive in nature.