Electromagnetic structure of octet baryons

Abstract

A numerical simulation of quenched QCD on a 24 X 12 X 12 X 24 lattice at /3= 5.9 is used to calculate the electric and magnetic form factors of the baryon octet. General forms of the baryon interpolating fields are considered. Magnetic moments, electric radii, magnetic radii, and magnetic transition moments are extracted from the form factors. The electric properties are found to be consistent with a quark-model picture involving spin-dependent forces. The lattice results for the magnetic properties show a mass and spin dependence of the effective quark moments which is not accounted for in conventional quark models. Lattice calculations underestimate the magnitude of electric radii, magnetic radii, and magnetic moments compared to experimental measurements. The finite volume of the periodic lattice may be responsible for the discrepancies. The pattern of electromagnetic radii in the lattice results are seen to be generally reproduced in the model results that are considered. The only exception is that of Z-which proves to be a sensitive probe of the quark dynamics. Lattice calculations indicate a positive value for the normalized square magnetic radius in Z-which contrasts Skyrme model results. Ratios of the magnetic moments allow a more detailed comparison with the experimental measurements. The lattice calculations are seen to better reproduce the experimental ratios than the model calculations.

Nucleon electromagnetic form factors

“…In an early pioneering work 6 of Leinweber, Woloshyn and Draper [Lei91], this was done in the so-called fixed current approach, which requires the current to have a fixed direction and to carry a fixed momentum. This method allows one to use different initial or final states without requiring further inversions, which is the time-consuming part of the calculation.…”

Electromagnetic form factors with FLIC fermions

“…The technique used for constructing the three-point functions follows the procedure outlined in detail in Refs. [13,14]. In particular, we use the sequential source technique at the current insertion.…”

Chiral extrapolation and physical insights

“…The best lattice calculations of the electromagnetic structure of baryons have so far been restricted to the quenched model of QCD [21,22]. Because of the absence of qq pair-creation, pion loop effects are typically suppressed in the quenched approximation [23,24,25].…”