Formation of eta-mesic nuclei by (pi,N) reaction and N^*(1535) in medium

TL;DR

This paper calculates eta-mesic nuclei formation spectra via (pi,N) reactions to explore in-medium properties of N^*(1535) and eta-nucleus interactions, providing guidance for future experiments at facilities like J-PARC.

Contribution

It presents theoretical formation spectra calculations for eta-mesic nuclei in (pi,N) reactions, linking in-medium N^*(1535) properties to observable spectra, which is a novel approach.

Findings

Clear formation spectra can reveal in-medium N^* and eta-nucleus interactions.

Experimental feasibility is demonstrated with specific reaction spectra.

Coincident pi N measurements can reduce background signals.

Abstract

We calculate formation spectra of eta-nucleus systems in (pi,N) reactions with nuclear targets, which can be performed at existing and/or forthcoming facilities, including J-PARC, in order to investigate eta-nucleus interactions. Based on the N^*(1535) dominance in the eta N system, eta-mesic nuclei are suitable systems for study of in-medium properties of the N^*(1535) baryon resonance, such as reduction of the mass difference of N and N^* in nuclear medium, which affects level structure of the eta and N^*-hole modes. We find that clear information on the in-medium N^*- and eta-nucleus interactions can be obtained through the formation spectra of the eta-mesic nuclei. We also discuss the experimental feasibilities by showing several spectra of (pi,N) reactions calculated with possible experimental settings. Coincident measurements of pi N pairs from the N^* decays in nuclei help us to reduce backgrounds.