Electromagnetic7Li form factors including meson-exchange contributions

Abstract

We have studied the transversal and longitudinal form factors of the7Li ground-state doublet within a microscopic triton + α model allowing for specific distortion effects in the internal triton cluster. Meson-exchange contributions were taken into account in form of the dominant isovector pion- and rho-meson-exchange currents. For the derivation of the respective two-body operators we have used a consistent microscopic formalism developed by Riska which guarantees that the continuity equation is satisfied. The consideration of meson-exchange contributions brings our calculation in better agreement with the data. We find that only the longitudinal inelastic form factor has a diffraction minimum belowq≈4fm−1, in agreement with the data. Although our approach reproduces the low-q form factors qualitatively well, we underestimate the data at the higher momentum transfers noticeably. Finally we find that the isoscalar part of the central force gives the dominant contribution to the exchange currents while the tensor force plays only a minor role due to cancellation effects between the pion- and rho-meson-exchange contributions.