Investigating the link between proton reaction cross sections and the quenching of proton spectroscopic factors in 48Ca

M.C Atkinson,W.H Dickhoff

doi:10.1016/j.physletb.2019.135027

Abstract

The nucleon self-energies of 40Ca and 48Ca are determined using a nonlocal dispersive optical model (DOM). By enforcing the dispersion relation connecting the real and imaginary part of the self-energy, scattering and structure data are used to constrain these self-energies. The ability to calculate both bound and scattering states simultaneously puts these self-energies in a unique position to consistently describe exclusive knockout reactions such as (e,e′p). The present analysis reveals the importance of high-energy proton reaction cross-section data in constraining spectroscopic factors required for the description of the (e,e′p) cross sections. In particular, it is imperative that high-energy proton reaction cross-section data are measured for 48Ca in the near future so that the quenching of the spectroscopic factors in the 48Ca(e,e′p)47K reaction can be unambiguously constrained using the DOM. Measurements of proton reaction cross sections in inverse kinematics employing rare isotope beams with large neutron excess will provide corresponding constraints on proton spectroscopic factors for exotic nuclei. Moreover, DOM generated spectral functions indicate that the quenching of spectroscopic factors compared to 40Ca is not only due to long-range correlation, but also partly due to the increase in high-momentum protons in 48Ca on account of the strong neutron-proton interaction. Single-particle momentum distributions of protons and neutrons in 48Ca calculated from these spectral functions confirm that neutron excess causes a higher fraction of high-momentum protons than neutrons.

Highlights

Independent particle models (IPMs) provide a simplified picture of the nucleus in which correlations are neglected and all orbitals are 100% filled up to the Fermi level according to the Pauli principle and those above it are empty
The dispersive optical model (DOM) analysis of the 40,48Ca(e, e p)39,47K reactions demonstrates that the addition of eight neutrons to 40Ca leads to a quenching of the proton spectroscopic factors, in agreement with the trend observed in Ref. [10] but with a reduced slope
The increase in the high-momentum content of protons in 48Ca is consistent with the np dominance picture, it contributes to the quenching of the spectroscopic factors

Summary

Introduction

Independent particle models (IPMs) provide a simplified picture of the nucleus in which correlations are neglected and all orbitals are 100% filled up to the Fermi level according to the Pauli principle and those above it are empty. The spectroscopic factors of orbitals are closely linked with the reaction cross section. This high-momentum content can be calculated in the DOM framework, which provides another means of investigating the quenching of the spectroscopic factor and many-body correlations in 40Ca and 48Ca. The Dyson equation determines the single-particle propagator or Green’s function G j(r, r ; E) from which bound-state and scattering observables can be deduced.

Results

Conclusion