Strange nucleon electromagnetic form factors from lattice QCD

TL;DR

This paper uses lattice QCD to compute strange and light quark contributions to nucleon electromagnetic form factors, revealing non-zero disconnected contributions at the percent level with high precision.

Contribution

The study provides the first high-precision lattice QCD results for both connected and disconnected contributions to nucleon form factors at near-physical pion mass.

Findings

Disconnected light quark contributions are non-zero at a few percent.

Strange form factors are at the percent level with large statistical uncertainties.

Results are consistent with zero within errors.

Abstract

We evaluate the strange nucleon electromagnetic form factors using an ensemble of gauge configurations generated with two degenerate maximally twisted mass clover-improved fermions with mass tuned to approximately reproduce the physical pion mass. In addition, we present results for the disconnected light quark contributions to the nucleon electromagnetic form factors. Improved stochastic methods are employed leading to high-precision results. The momentum dependence of the disconnected contributions is fitted using the model-independent z-expansion. We extract the magnetic moment and the electric and magnetic radii of the proton and neutron by including both connected and disconnected contributions. We find that the disconnected light quark contributions to both electric and magnetic form factors are non-zero and at the few percent level as compared to the connected. The strange form factors are also at the percent level but more noisy yielding statistical errors that are typically within one standard deviation from a zero value.