paper

Form Factors of the Nucleon Axial Current

arXiv:2011.14026 · doi:10.1016/j.physletb.2021.136150

Abstract

A symmetry-preserving PoincarÃ©-covariant quark+diquark Faddeev equation treatment of the nucleon is used to deliver parameter-free predictions for the nucleon's axial and induced pseudoscalar form factors, $G_{A}$ and $G_{P}$ , respectively. The result for $G_{A}$ can reliably be represented by a dipole form factor characterised by an axial charge $g_{A} = G_{A} (0) = 1.25 (3)$ and a mass-scale $M_{A} = 1.23 (3) m_{N}$ , where $m_{N}$ is the nucleon mass; and regarding $G_{P}$ , the induced pseudoscalar charge $g_{p}^{*} = 8.80 (23)$ , the ratio $g_{p}^{*} / g_{A} = 7.04 (22)$ , and the pion pole dominance Ansatz is found to provide a reliable estimate of the directly computed result. The ratio of flavour-separated quark axial charges is also calculated: $g_{A}^{d} / g_{A}^{u} = - 0.16 (2)$ . This value expresses a marked suppression of the size of the $d$ -quark component relative to that found in nonrelativistic quark models and owes to the presence of strong diquark correlations in the nucleon Faddeev wave function -- both scalar and axial-vector, with the scalar diquark being dominant. The predicted form for $G_{A}$ should provide a sound foundation for analyses of the neutrino-nucleus and antineutrino-nucleus cross-sections that are relevant to modern accelerator neutrino experiments.

8 pages, 6 figures, 2 tables. Accepted for publication in Phys. Lett. B