Ab Initio Study of the Radii of Oxygen Isotopes

We present an 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 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.