Ab initio study of the radii of oxygen isotopes

TL;DR

This study uses nuclear lattice effective field theory with advanced algorithms to accurately compute charge and matter radii of oxygen isotopes, providing benchmarks and highlighting experimental ambiguities.

Contribution

It introduces the partial pinhole algorithm to improve Monte Carlo efficiency in ab initio nuclear radius calculations, extending capabilities to neutron-rich isotopes.

Findings

Computed charge radii match experimental data for several isotopes.

Predicted charge radius for $^{20}$O is 2.810(32) fm.

Calculated matter radii agree with scattering data but differ from cross section measurements.

Abstract

We present an {\em ab initio} study of the charge and matter radii of oxygen isotopes from $^{16}$O to $^{20}$O using nuclear lattice effective field theory (NLEFT) with high-fidelity N$^3$LO chiral interactions. To efficiently address the Monte Carlo sign problem encountered in nuclear radius calculations, we introduce the {\em partial pinhole algorithm}, significantly reducing statistical uncertainties and extending the reach to more neutron-rich and proton-rich isotopes. Our computed charge radii for $^{16}$O, $^{17}$O, and $^{18}$O closely match experimental data, and we predict a charge radius of $2.810(32)$ fm for $^{20}$O. The calculated matter radii show excellent agreement with values extracted from low-energy proton and electron elastic scattering data, but are inconsistent with those derived from interaction cross sections and charge-changing cross section measurements. These discrepancies highlight model-dependent ambiguities in the experimental extraction methods of matter radii and underscore the value of precise theoretical benchmarks from NLEFT calculations.