Unified model of nucleon elastic form factors and implications for neutrino-oscillation experiments

TL;DR

This paper develops a light-front quark-diquark model with pion cloud to accurately predict nucleon form factors, revealing significant deviations from common approximations and implications for neutrino oscillation experiments.

Contribution

It introduces a novel light-front model calibrated to electromagnetic data to predict the axial form factor, improving the modeling of neutrino-nucleon interactions.

Findings

Predicted axial charge radius squared: 0.29 ± 0.03 fm².

Dipole approximation overestimates cross sections by 5-10%.

Implications for DUNE experiment flux-averaged cross sections.

Abstract

Precise knowledge of the nucleon's axial-current form factors is crucial for modeling GeV-scale neutrino-nucleus interactions. Unfortunately, the axial form factor remains insufficiently constrained to meet the precision requirements of upcoming long-baseline neutrino-oscillation experiments. This work studies the nucleon's axial and vector form factors using the light-front approach to build a quark-diquark model of the nucleon with an explicit pion cloud. The light-front wave functions in both the quark and pion-baryon Fock spaces are first calibrated to existing experimental information on the nucleon's electromagnetic form factors, and then used to predict the axial form factor. The resulting squared charge radius of the axial pseudo-vector form factor is predicted to be $r_A^2\! =\! 0.29\! \pm\! 0.03\, \mathrm{fm}^2$, where the small error accounts for the model's parametric uncertainty. We use our form factor results to explore the (quasi-)elastic scattering of neutrinos by (nuclei)nucleons, with the result that the the widely-implemented dipole ansatz is an inadequate approximation of the full form factor for modeling both processes. The approximation leads to a $5\!-\!10\%$ over-estimation of the total cross section, depending on the (anti)neutrino energy. We project over-estimations of similar size in the flux-averaged cross sections for the upcoming DUNE long-baseline neutrino-oscillation experiment.