Zemach and Friar radii of the proton and neutron from lattice QCD

Abstract

We present the first lattice-QCD result for the Zemach and Friar radii of the proton and neutron. Our calculation includes both quark-connected and -disconnected diagrams and assesses all sources of systematic uncertainties arising from excited-state contributions, finite-volume effects, and the continuum extrapolation. At the physical point, we obtain for the proton rZp=(1.013±0.010(stat)±0.012(syst))  fm and rFp=(1.301±0.012(stat)±0.014(syst))  fm. These numbers suggest small values of the Zemach and Friar radii of the proton but are compatible with most of the experimental studies. Published by the American Physical Society 2024