Spectroscopic factors, overlaps, and isospin symmetry from an $R$-matrix point of view

TL;DR

This paper uses $R$-matrix theory to derive relationships among spectroscopic factors, overlaps, and isospin symmetry, clarifying their connections and applying the methods to nuclear mirror states, with implications for astrophysical reaction rates.

Contribution

It provides a systematic derivation of relationships among key nuclear structure quantities using $R$-matrix theory, including a new approach to multi-level mirror symmetry.

Findings

Relationships among spectroscopic factors, overlaps, and isospin symmetry are established.

Application to mirror nuclei demonstrates significant differences in asymptotic normalization constants.

Implications for astrophysical reaction rates, notably in novae, are identified.

Abstract

Background: Spectroscopic factors, overlaps, and isospin symmetry are often used in conjunction with single-particle wave functions for the phenomenological analysis of nuclear structure and reactions. Many differing prescriptions for connecting these quantities to physically relevant asymptotic normalization constants or widths are available in the literature, but their relationship and degree of validity are not always clear. Purpose: This paper derives relationships among the above quantities of interest using well-defined methodology and starting assumptions. Method: $R$-matrix theory is used as the primary tool to interoperate between the quantities of interest to this work. Particular attention is paid to effects arising from beyond the nuclear surface, where isospin symmetry is strongly violated. Results: Relationships among the quantities of interest are derived. Example applications of these methods to mirror levels in nucleon+${}^{12}{\rm C}$, nucleon+${}^{16}{\rm O}$, and nucleon+${}^{26}{\rm Al}$ are presented. A new approach to multi-level mirror symmetry is derived and applied to the first three $2^+$ states of ${}^{18}{\rm O}$ and ${}^{18}{\rm Ne}$. Conclusions: The relationship between the quantities of interest is clarified and certain procedures are recommended. It is found that the asymptotic normalization constant of the second $2^+$ state in ${}^{18}{\rm Ne}$ deduced from the mirror state in ${}^{18}{\rm O}$ is significantly larger than found in previous work. This finding has the effect of increasing the ${}^{17}{\rm F}(p,\gamma){}^{18}{\rm Ne}$ reaction rate in novae.