Chiral limit of nucleon lattice electromagnetic form factors

Abstract

We calculate electric and magnetic form factors of protons and neutrons in quenched Monte Carlo lattice QCD on a ${16}^3$ × 24 lattice at $\beta =6.0\mathrm{}$ using Wilson fermions. We employ a method which characterizes one of the nucleon fields as a fixed zero-momentum secondary source. Extrapolating the overall data set to the chiral limit, we find acceptable fits for either dipole or monopole forms and extract proton and neutron magnetic moments, the magnitude of which are 10 to 15% low compared to experiment. In the extrapolation of the dipole fit of the form factors, we find that the dipole-to-nucleon mass ratio is about 7% low compared to experiment. In addition, we obtain positive values of the neutron electric form factor, which, however, are poorly represented by a popular phenomenological form at intermediate to small $\kappa$ values. A zero-momentum technique for extracting hadron magnetic moments is briefly discussed and shown to yield unrealistically small magnetic moment values.