Ab initio charge form factors and radii of light isoscalar nuclei: Role of the two-body charge density

TL;DR

This study uses ab initio methods with chiral interactions to predict charge form factors and radii of light isoscalar nuclei, emphasizing the importance of two-nucleon charge densities for accurate results.

Contribution

It demonstrates the crucial role of two-nucleon charge operators in ab initio calculations of nuclear charge form factors and radii, improving agreement with experimental data.

Findings

Good agreement of FFs and radii with experimental data

Two-nucleon charge density contributions are essential at intermediate and large momentum transfers

Two-nucleon charge operators are key to resolving underestimation of charge radii

Abstract

We make \textit{ab initio} predictions of charge form factors (FFs) and radii for the isoscalar nuclei $^6$Li and $^8$Be using the Jacobi-coordinate No-Core Shell Model. The calculations employ chiral semilocal momentum-space regularized two- and three-nucleon interactions, together with consistently regularized one- and two-nucleon electromagnetic charge operators. With the short-range charge density fixed to the $^4$He charge radius, the predicted FFs and the $^6$Li radius show good agreement with available experimental data. We find that two-nucleon charge density contributions are essential for describing the FFs, particularly at intermediate and large momentum transfers. Although their influence on the charge radii is limited, these contributions remain crucial for attaining accurate predictions. The present results highlight the importance of two-nucleon charge operators in addressing the long-standing underestimation of nuclear charge radii in \textit{ab initio} calculations based on modern chiral interactions.