The shape of the $Δ$ baryon in a covariant spectator quark model

Abstract

Using a covariant spectator quark model that describes the recent lattice QCD data for the $Δ$ electromagnetic form factors and all available experimental data on $γN \to Δ$ transitions, we analyze the charge and magnetic dipole distributions of the $Δ$ baryon and discuss its shape. We conclude that the quadrupole moment of the $Δ$ is a good indicator of the deformation and that the $Δ^+$ charge distribution has an oblate shape. We also calculate transverse moments and find that they do not lead to unambiguous conclusions about the underlying shape.

Extended introduction, references added, other small modifications. To appear in Phys. Rev. D. 14 pages, 8 figures