Sea quarks contribution to the nucleon magnetic moment and charge radius at the physical point

摘要

We report a comprehensive analysis of the light and strange disconnected-sea quarks contribution to thenucleon magnetic moment, charge radius, and the electric and magnetic form factors. The lattice QCDcalculation includes ensembles across several lattice volumes and lattice spacings with one of theensembles at the physical pion mass.We adopt a model-independent extrapolation of the nucleon magneticmoment and the charge radius. We have performed a simultaneous chiral, infinite volume, and continuumextrapolation in a global fit to calculate results in the continuum limit. We find that the combined lightand strange disconnected-sea quarks contribution to the nucleon magnetic moment is μ_M(DI) =−0.022(11)(09) μ_N and to the nucleon mean square charge radius is _E(DI) = −0.019(05)(05) fm~2 which is about 1/3 of the difference between the _E of electron-proton scattering and that of a muonic atom and so cannot be ignored in obtaining the proton charge radius in the lattice QCD calculation. Themost important outcome of this lattice QCD calculation is that while the combined light-sea and strangequarks contribution to the nucleon magnetic moment is small at about 1%, a negative 2.5(9)% contributionto the proton mean square charge radius and a relatively larger positive 16.3(6.1)% contribution to theneutron mean square charge radius come from the sea quarks in the nucleon. For the first time, byperforming global fits, we also give predictions of the light and strange disconnected-sea quarkscontributions to the nucleon electric and magnetic form factors at the physical point and in the continuumand infinite volume limits in the momentum transfer range of 0 ≤ Q~2 ≤ 0.5 GeV~2.