Single pion-production and pion propagation in Achilles

TL;DR

This paper enhances the Achilles neutrino interaction simulator by incorporating detailed single-pion production and propagation mechanisms, validated against various experimental data, to improve accuracy in modeling neutrino-nucleus interactions.

Contribution

It introduces a fully exclusive modeling of single-pion production in Achilles using advanced dynamical coupled-channels and realistic nuclear spectral functions.

Findings

Validated against pion-nucleon and pion-nucleus scattering data.

Compared with electron- and neutrino-nucleus measurements from multiple experiments.

Demonstrated improved modeling of pion production and propagation processes.

Abstract

We extend the applicability of Achilles (A CHIcagoLand Lepton Event Simulator) by incorporating the single-pion production mechanism in a fully exclusive fashion. The electroweak interaction vertex is modeled by combining the state-of-the-art Dynamical Coupled-Channels approach with realistic hole spectral functions, which account for correlations in both the initial target state and the residual spectator system. Final-state interactions are treated using a semi-classical intranuclear cascade that leverages nuclear configurations to determine the correlated spatial distribution of protons and neutrons. The meson-baryon scattering amplitudes used in the cascade are computed within the Dynamical Coupled-Channels framework, consistent with the electroweak vertex. To model pion absorption, we employ the optical potential approach of Oset and Salcedo. As an alternative approach, we explicitly model the production and propagation of resonances which mediate pion-nucleon scattering and pion absorption. We validate out approach against pion-nucleon and pion-nucleus scattering data, and present comparisons with electron- and neutrino-nucleus measurements from e4$\nu$, T2K, MINER$\nu$A, and MicroBooNE.