The Nucleon Axial Form Factor from Elementary Target Data

TL;DR

This paper evaluates constraints on the nucleon axial form factor from various datasets, highlighting tensions between hydrogen and deuterium data and providing improved parameterizations for use in neutrino physics.

Contribution

It offers a comprehensive analysis of elementary target data, lattice QCD, and recent hydrogen data to refine the nucleon axial form factor and address discrepancies in existing measurements.

Findings

Significant tension between hydrogen and deuterium data.

Deuterium data may underestimate the form factor's central value and uncertainty.

Provides $z$ expansion parameterizations for the axial form factor.

Abstract

Precise neutrino-nucleon amplitudes are essential ingredients for predicting neutrino event rates in current and upcoming long-baseline neutrino oscillation experiments. A common neutrino interaction with a low reaction threshold and with most of the energy carried by two final state particles is quasielastic scattering, for which the nucleon axial form factor, $F_{A}(Q^{2})$, is a dominant source of uncertainty. Improvements to the nucleon axial form factor rely on neutrino scattering data with elementary targets to reduce or eliminate the need for nuclear modeling systematics. This work examines constraints on the nucleon axial form factor that can be achieved from datasets of neutrino scattering on deuterium targets, Lattice QCD predictions, and from the recent hydrogen target data from the MINERvA Collaboration. Significant tension is found between hydrogen and deuterium target data, suggesting that extractions from deuterium underestimate both the central value and uncertainty of the form factor. Parameterizations for and uncertainties of the nucleon axial form factor using the $z$ expansion are provided.