Spin-orbital structure of the nucleon magnetic moment

How the nucleon magnetic moment originates from the quark spin and orbital motions is an important issue of the nucleon structure. The Gordon decomposition separates the quark vector current and magnetic moment into a spin and an orbital parts. We show that the spin part is related to the quark tensor charge, thus can be determined experimentally and computed reliably by lattice QCD. Knowledge of the spin-orbital structure of the nucleon magnetic moment would also shed light on the nucleon spin problem. As an example, we show that the spin part of the nucleon strangeness magnetic moment ${\ensuremath{\mu}}_{s}$ is negative. If the experimental result of a positive ${\ensuremath{\mu}}_{s}$ is confirmed, then the orbital motion of strange quarks must be important in the nucleon.