Study of Δ excitations in medium-mass nuclei with peripheral heavy ion charge-exchange reactions

J L Rodríguez-Sánchez ,H Weick,E Casarejos,C Scheidenberger,J Benlliure,J Atkinson,H Lenske,T Aumann,K Boretzky,M Caamaño,S Beceiro-Novo,M Takechi,C Paradela,E Haettner,A Kelić-Heil,D Cortina-Gil,Y Ayyad,H Álvarez‐Pol ,Y K Tanaka ,D Pérez–Loureiro ,P Fernåndez ,H Geißel ,Yu A Litvinov ,S Piétri ,A Procházka ,Isaac Vidaña ,J E Ramirez Vargas ,A Estradé ,J S Winfield

doi:10.1016/j.physletb.2020.135565

Abstract

Isobaric single charge-exchange reactions, changing nuclear charges by one unit but leaving the mass partitions unaffected, have been for the first time investigated by peripheral collisions of 112Sn ions accelerated up to 1A GeV at the GSI facilities. The high-resolving power of the FRS spectrometer allows us to obtain (p,n)-type isobaric charge-exchange cross sections with an uncertainty of 3.5% and to separate quasi-elastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic component is associated to the excitation of the Δ(1232) isobar resonance and the emission of pions in s-wave both in the target and projectile nucleus, while the quasi-elastic contribution is associated to the nuclear spin-isospin response of nucleon-hole excitations. An apparent shift of the Δ-resonance peak of ∼63 MeV is observed when comparing the missing-energy spectra obtained from the measurements with proton and carbon targets. A detailed analysis, performed with a theoretical model for the reactions, indicates that this observation can be simply interpreted as a change in the relative magnitude between the contribution of the excitation of the resonance in the target and in the projectile.

Highlights

In the past, many experimental and theoretical attempts have been made to clarify the complexities of the interplay of nucleons and excitations of the nucleon in a nuclear many-body environment
In-medium resonance physics is of central importance to understand the meson yields with and without strangeness observed in central heavy ion collisions, e.g. measured at the FOPI and HADES experiments at the GSI facility
Isobaric single charge-exchange reactions induced by ions of 112Sn at energies of 1 A GeV on different targets have been investigated at GSI using the FRS spectrometer

Summary

Introduction

Many experimental and theoretical attempts have been made to clarify the complexities of the interplay of nucleons and excitations of the nucleon in a nuclear many-body environment. We use isobaric single charge-exchange reactions induced by relativistic beams of stable medium-mass projectiles as a tool to study the excitation of nucleon resonances in nuclear matter. These reactions where the projectile and target nuclei exchange one nucleon and the projectile and ejectile contain the same number of nucleons guarantee that, with a large probability, the charge-exchange process is mediated by a quasi-free nucleon-nucleon collision [21,22]. We compare our experimental data to some sophisticated model calculations in order to understand the energy shift observed in the -peak

Experimental approach

Model calculations

Results and discussion

Summary and conclusions