A Lattice QCD Analysis of the Strangeness Magnetic Moment of the Nucleon

The outcome of the SAMPLE Experiment suggests that the strange-quark contribution to the nucleon magnetic moment, GM (0), may be greater than zero. This result is very difficult to reconcile with expectations based on the successful baryon magnetic-moment phenomenology of the constituent quark model. We show that careful consideration of chiral symmetry reveals some rather unexpected properties of QCD. In particular, it is found that the valence u-quark contribution to the magnetic moment of the neutron can differ by more than 50% from its contribution to the Ξ0 magnetic moment. This hitherto unforeseen result leads to the value GM (0) = −0.16± 0.18 with a systematic error, arising from the relatively large strange quark mass used in existing lattice calculations, that would tend to shift GM (0) towards small positive values. ∗[email protected] †[email protected]