High-precision calculation of the strange nucleon electromagnetic form factors

We report a direct lattice QCD calculation of the strange nucleon electromagnetic form factors $G_E^s$ and $G_M^s$ in the kinematic range $0 \leq Q^2 \lesssim 1.2\: {\rm GeV}^2$. For the first time, both $G_E^s$ and $G_M^s$ are shown to be nonzero with high significance. This work uses closer-to-physical lattice parameters than previous calculations, and achieves an unprecedented statistical precision by implementing a recently proposed variance reduction technique called hierarchical probing. We perform model-independent fits of the form factor shapes using the $z$-expansion and determine the strange electric and magnetic radii and magnetic moment. We compare our results to parity-violating electron-proton scattering data and to other theoretical studies.

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