The power of two: Assessing the impact of a second measurement of the weak-charge form factor of 208Pb

TL;DR

This paper evaluates how a second measurement of the weak-charge form factor of 208Pb can improve understanding of its neutron distribution and the equation of state of neutron-rich matter, using Bayesian calibration of a symmetrized Fermi model.

Contribution

It introduces a method to use two experimental points of the weak-charge form factor to accurately determine the neutron distribution in 208Pb with a symmetrized Fermi function.

Findings

Two measurements suffice to calibrate the model accurately.

A second measurement significantly constrains the neutron distribution.

The approach links weak-charge form factor data to nuclear matter properties.

Abstract

[Background] Besides its intrinsic value as a fundamental nuclear-structure observable, the weak-charge density of 208Pb - a quantity that is closely related to its neutron distribution - is of fundamental importance in constraining the equation of state of neutron-rich matter. [Purpose] To assess the impact that a second electroweak measurement of the weak-charge form factor of 208Pb may have on the determination of its overall weak-charge density. [Methods] Using the two putative experimental values of the form factor, together with a simple implementation of Bayes' theorem, we calibrate a theoretically sound - yet surprisingly little known - symmetrized Fermi function, that is characterized by a density and form factor that are both known exactly in closed form. [Results] Using the charge form factor of 208Pb as a proxy for its weak-charge form factor, we demonstrate that using only two experimental points to calibrate the symmetrized Fermi function is sufficient to accurately reproduce the experimental charge form factor over a significant range of momentum transfers. [Conclusions] It is demonstrated that a second measurement of the weak-charge form factor of 208Pb supplemented by a robust theoretical input in the form of the symmetrized Fermi function, would place significant constraints on the neutron distribution of 208Pb and, ultimately, on the equation of state of neutron-rich matter.