Strange Quark Magnetic Moment of the Nucleon at Physical Point

TL;DR

This paper presents a lattice QCD calculation of the strange quark contributions to the nucleon's magnetic moment and charge radius at the physical pion mass, providing the first direct determination of these form factors.

Contribution

It introduces a model-independent method to extract strange electromagnetic form factors at the physical point using lattice QCD with multiple lattice spacings and volumes.

Findings

Strange magnetic moment G^s_M(0) = -0.064(14)(09) μ_N

Strange charge radius ⟨r_s^2⟩_E = -0.0043(16)(14) fm^2

Achieved four-sigma statistical precision

Abstract

We report a lattice QCD calculation of the strange quark contribution to the nucleon's magnetic moment and charge radius. This analysis presents the first direct determination of strange electromagnetic form factors including at the physical pion mass. We perform a model-independent extraction of the strange magnetic moment and the strange charge radius from the electromagnetic form factors in the momentum transfer range of $0.051 \,\text{GeV}^2 \lesssim Q^2 \lesssim 1.31 \,\text{GeV}^2 $. The finite lattice spacing and finite volume corrections are included in a global fit with $24$ valence quark masses on four lattices with different lattice spacings, different volumes, and four sea quark masses including one at the physical pion mass. We obtain the strange magnetic moment $G^s_M(0) = - 0.064(14)(09)\, \mu_N$. The four-sigma precision in statistics is achieved partly due to low-mode averaging of the quark loop and low-mode substitution to improve the statistics of the nucleon propagator. We also obtain the strange charge radius $\langle r_s^2\rangle_E = -0.0043 (16)(14)\,$ $\text{fm}^2$.