Deuteron properties of the coupled nucleon and isobar channels model

Abstract

The system of NN, NΔ, ΔΔ, and ${\mathrm{NN}}^{\mathrm{*}}$(1440) channels, coupled by long-range meson exchange forces and a short-range boundary condition, has been successfully applied to medium energy NN scattering. The deuteron system includes the NN${(}^3$ ${\mathit{S}}_1$, ${}_{}{}^3{}_{}{}^{}$ ${\mathit{D}}_1$), ΔΔ${(}^3$ ${\mathit{S}}_1$, ${}_{}{}^3{}_{}{}^{}$ ${\mathit{D}}_1$, ${}_{}{}^7{}_{}{}^{}$ ${\mathit{D}}_1$), and NN*${(}^3$ ${\mathit{S}}_1$) channels. The scattering data for nucleon $T_{\mathrm{lab}<1\mathrm{}}$ GeV put strong restrictions on the short-range parameters of the model, imposing ∼2% total isobar content in the deuteron, but do not determine the relative strength of coupling among the isobar channels. In contrast, the deuteron elastic magnetic form factor is sensitive to the mixture of isobars. Adding meson exchange current contributions, a good fit to these data can be achieved, including a nontrivial prediction of a minimum near $q^2$=50 ${\mathrm{fm}}^{\mathrm{-}2}$, by a balance between ΔΔ${(\mathrm{}}^3$ $D_1$,${\mathrm{}}^7$ $D_1$) components. Balancing ΔΔ${(\mathrm{}}^3$ $S_1$,${\mathrm{}}^7$ $D_1$) with ${\mathrm{NN}}^{\mathrm{*}}$ ${(\mathrm{}}^3$ ${\mathrm{S}}_1$), assuming a negative ${\mathrm{N}}^{\mathrm{*}}$ isoscalar magnetic moment, is only adequate for $q^2$${\mathrm{fm}}^{\mathrm{-}2}$. The static properties of the deuteron are well fitted, and the electric and tensor polarization form factors are consistent with the data. The inclusion of the lowest six-quark state, with cloudy bag model dynamics, increases the boundary radius, requiring ∼7% isobar content proportioned as above to approximately fit the data.