Two-component model for the axial form factor of the nucleon

Abstract

The axial form factor of the nucleon is studied in a two-component model consisting of a three-quark intrinsic structure surrounded by a meson cloud. The experimental data in the space-like region are well reproduced with a minimal number of parameters. The results are similar to those obtained from a dipole fit up to 1 GeV${}^2$, but they surprisingly show a zero between 2 and 3 GeV${}^2$. Such behavior, predicted by the present model completely disagrees with the dipole parametrization. The theoretical expression for the form factor is then analytically extrapolated to the time-like region, giving the first predictions in this regime. This kinematical region is especially interesting for present and future colliders.

Comments: 12 pages 2 figures Final version to appear in Phys. Rev. C