Abstract
We present a model for the study of the excitation of Δ(1232) and N * (1440) resonances in isobaric charge-exchange ( A Z , A ( Z ± 1)) reactions of heavy nuclei. Quasi-elastic and inelastic elementary processes contributing to the double differential cross sections of the reactions are described in terms of the exchange of virtual pions. The inelastic channel includes processes where the resonances are excited both in the target and in the projectile nucleus. We present results for reactions of 112 Sn and 124 Sn on different targets. Our results confirm that the position of the Δ peak is insensitive to targets with mass number A ≥ 12, and show that the origin of the Δ peak shift towards low excitation energies, with respect to its position in reactions with a proton target, can be easily explained in terms of the superposition of the different excitation mechanisms contributing to the reaction.
Highlights
Determining the in-medium properties of nucleon resonances is essential for a better understanding of the underlying dynamics governing many nuclear reactions
Our results confirm that the position of the Δ peak is insensitive to targets with mass number A ≥ 12, and show that the origin of the Δ peak shift towards low excitation energies, with respect to its position in reactions with a proton target, can be explained in terms of the superposition of the different excitation mechanisms contributing to the reaction
Three elementary processes contribute to the total double differential cross section of this reaction, the process p(p, n)Δ++ where a Δ++ is excited in the target and it decays into pπ+, and the processes p(p, Δ+)n and p(p, P+11)n in which a Δ+ or are excited in the projectile the charge and after tshteaytedPe+1c1ayofitnhenπN+∗
Summary
Determining the in-medium properties of nucleon resonances is essential for a better understanding of the underlying dynamics governing many nuclear reactions. Isobaric charge-exchange reactions are interesting because, at low energy, they allow the investigation of spin-isospin nuclear excitations (Gamow–Teller, spindipole, spin-quadrupole, ...) and, at medium and high energies, the excitation of nucleon resonances such as e.g., the Δ(1232) isobar or the Roper N∗(1440) They can provide valuable information on the radial distribution of neutrons and protons in nuclei. A experimental program completely devoted to study the excitation of this resonance in reactions with light and medium mass projectiles was performed at the SATURNE accelerator in Saclay during those years [6] Those experiments showed that the position of the Δ peak was shifted towards low excitation energies by ∼ 70 MeV when using a target with mass number A ≥ 10 as compared to its position in reactions with a proton target. In the following we describe briefly these two pieces of the model
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