Understanding Neutrons in Neutrino Experiments

Neutrons pose a significant challenge in neutrino experiments where energy reconstruction is critical. The behavior of neutrons is particularly model-dependent because they can take away interaction energy that is largely unseen owing to their non-ionizing nature. As a result, we must devise systematic uncertainties to quantify our understanding of both neutron production from a neutrino interaction and neutron propagation through the detector medium. Here, I will discuss two experiments based at Fermilab that seek to constrain both of these uncertainties: 1) the long-baseline neutrino oscillation experiment NOvA and 2) the Accelerator Neutrino Neutron Interaction Experiment (ANNIE). In NOvA, we have implemented a supplementary neutron-on-carbon inelastic scattering model for medium energy neutrons that has shown an improved agreement between data and simulation. While ANNIE is a gadolinium-doped water Cherenkov detector with a rich R&D program and a primary physics goal of measuring neutron production from neutrino interactions.