Precision calculation of the electromagnetic radii of the proton and neutron from lattice QCD

TL;DR

This paper uses lattice QCD to accurately compute the electromagnetic radii and magnetic moments of protons and neutrons, including all relevant contributions and systematic effects.

Contribution

It provides the first comprehensive lattice QCD calculation of both connected and disconnected contributions to nucleon electromagnetic form factors at the physical point.

Findings

Proton electric radius: 0.820(14) fm

Proton magnetic radius: 0.8111(89) fm

Proton magnetic moment: 2.739(66)

Abstract

We present lattice-QCD results for the electromagnetic form factors of the proton and neutron including both quark-connected and -disconnected contributions. The parametrization of the $Q^2$-dependence of the form factors is combined with the extrapolation to the physical point. In this way, we determine the electric and magnetic radii and the magnetic moments of the proton and neutron. For the proton, we obtain at the physical pion mass and in the continuum and infinite-volume limit $\sqrt{\langle r_E^2 \rangle^p} = 0.820(14)$ fm, $\sqrt{\langle r_M^2 \rangle^p} = 0.8111(89)$ fm, and $\mu_M^p = 2.739(66)$, where the errors include all systematics.