Abstract
The role of the strange quarks on the low-energy interactions of the proton can be probed through the strange electromagnetic form factors. Knowledge of these form factors provides essential input for parity-violating processes and contributes to the understanding of the sea quark dynamics. We determine the strange electromagnetic form factors of the nucleon within the lattice formulation of Quantum Chromodynamics using simulations that include light, strange and charm quarks in the sea all tuned to their physical mass values. We employ state-of-the-art techniques to accurately extract the form factors for values of the momentum transfer square up to 0.8~GeV$^2$. We find that both the electric and magnetic form factors are statistically non-zero. We obtain for the strange magnetic moment $\mu^s=-0.017(4)$, the strange magnetic radius $\langle r^2_M \rangle^s=-0.015(9)$~fm$^2$, and the strange charge radius $\langle r^2_E \rangle^s=-0.0048(6)$~fm$^2$.
Highlights
Strange quarks are the lightest nonvalance quarks in the nucleon and the most likely constituents to contribute to sea-quark dynamics
We determine the strange electromagnetic form factors of the nucleon within the lattice formulation of quantum chromodynamics using simulations that include light, strange and charm quarks in the sea all tuned to their physical mass values
We obtain for the strange magnetic moment μs 1⁄4 −0.017ð4Þðþ0 1Þðþ0 5Þ, the strange magnetic radius hr2Mis 1⁄4 −0.015ð9Þðþ0 3Þðþ0 4Þ fm2, and the strange charge radius hr2Eis 1⁄4 −0.0048ð6Þð0−8Þðþ0 12Þ fm2, where the first error is statistical, and the second and third systematic
Summary
Strange quarks are the lightest nonvalance quarks in the nucleon and the most likely constituents to contribute to sea-quark dynamics. The experimental program to study the strangeness in the proton began with the SAMPLE experiment [11,12] and it has been continuing with the series of A4 experiments at the Mainz Microtron accelerator facility [13,14,15], and the HAPPEX [16,17,18,19] and G0 experiments [20,21] at JLab. to date, the experimental results, indicating nonzero values, carry large errors that make them inconclusive. The experimental results, indicating nonzero values, carry large errors that make them inconclusive This is confirmed by a recent global analysis of parity-violating elastic scattering data [22], where, a negative magnetic strange form factor is indicated, the large error still makes it consistent with zero. A review of the experimental program and results can be found in Ref. [23]
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