Nuclear de-excitations in low-energy charged-current νe scattering on 40Ar

Background: Large argon-based neutrino detectors, such as those planned for the Deep Underground Neutrino Experiment, have the potential to provide unique sensitivity to low-energy (few to tens of MeV) electron neutrinos produced by core-collapse supernovae. Despite their importance for neutrino energy reconstruction, nuclear de-excitations following charged-current nu(e) absorption on Ar-40 have never been studied in detail at supernova energies. Purpose: I develop a model of nuclear de-excitations that occur following the Ar-40(nu(e), e(-))K-40+ reaction. This model is applied to the calculation of exclusive cross sections. Methods: A simple expression for the inclusive differential cross section is derived under the allowed approximation. Nuclear de-excitations are described using a combination of measured gamma-ray decay schemes and the Hauser-Feshbach statistical model. All calculations are carried out using a novel Monte Carlo event generator called MARLEY (Model of Argon Reaction Low Energy Yields). Results: Various total and differential cross sections are presented. Two de-excitation modes, one involving only gamma rays and the other including single neutron emission, are found to be dominant at few tens-of-MeV energies. Conclusions: Nuclear de-excitations have a strong impact on the achievable energy resolution for supernova nu(e) detection in liquid argon. Tagging events involving neutron emission, though difficult, could substantially improve energy reconstruction. Given a suitable calculation of the inclusive cross section, the MARLEY nuclear de-excitation model may readily be applied to other scattering processes.

Automated summary

This study develops a model for nuclear de-excitations following the reaction of Ar-40(nu(e), e(-))K-40+ and applies it to calculate exclusive cross sections, revealing the significant impact of nuclear de-excitations on energy resolution in liquid argon for supernova nu(e) detection, especially at energies of a few tens of MeV. The MARLEY nuclear de-excitation model, with suitable inclusive cross section calculations, can be readily applied to other scattering processes.