Two-body current and axial form factor effects in charged-current quasielastic neutrino-nucleus scattering within the NEUT event generator

TL;DR

This paper develops a detailed model for charged-current quasielastic neutrino-nucleus scattering, incorporating two-body currents and various axial form factors, and benchmarks it against experimental data.

Contribution

It introduces an improved spectral function model with meson-exchange currents in the NEUT generator, tested against T2K and MINERvA data, highlighting the impact of two-body currents and form factor choices.

Findings

Two-body meson-exchange currents significantly increase the total cross section.

Different axial form factor parametrizations yield varying cross section predictions.

The LQCD+MINERvA fit overestimates the experimental data, while the MINERvA-only fit aligns better.

Abstract

We present a charged-current quasielastic neutrino-nucleus scattering model based on an unfactorized representation of the spectral function, employing relativistic momentum distributions for bound nucleons and the relativistic distorted-wave impulse approximation with an energy-dependent relativistic potential to describe the scattered nucleon. The model incorporates two-body meson-exchange currents contributing to one-particle-one-hole final states and tests several axial form factor parametrizations, including recent LQCD and MINERvA fits. It is implemented in the NEUT event generator and benchmarked against T2K and MINERvA ${\nu}_{\mu}$-$^{12}$C CC0${\pi}$ measurements. We find that two-body meson-exchange currents lead to a sizeable increase of the total cross section, arising from an enhancement of the transverse response, which is the dominant component in charged-current neutrino scattering. On the other hand, recent fits of the axial form factor predict larger values than the standard dipole form, yielding a systematic enhancement of the cross section. The LQCD+MINERvA parametrization tends to overestimate the data, while the MINERvA-only fit provides a more moderate increase. Overall, no single configuration consistently provides the best agreement with the different datasets.