Forbidden transitions in neutral and charged current interactions between low-energy neutrinos and Argon

Background: The study of low-energy neutrinos and their interactions with atomic nuclei is crucial to several open problems in physics, including the neutrino mass hierarchy, CP-violation, candidates of Beyond Standard Model physics and supernova dynamics. Examples of experiments include CAPTAIN at SNS as well as DUNE's planned detection program of supernova neutrinos. Purpose: We present cross section calculations for quasielastic charged current and neutral current neutrinos at low energies, with a focus on $^{40}$Ar. We also take a close look at pion decay-at-rest neutrino spectra, which are used in e.g. the SNS experiment at Oakridge. Method and results: We employ a Hartree Fock + Continuum Random Phase Approximations (HF+CRPA) framework, which allows us to model the responses and include the effects of long-range correlations. It is expected to provide a good framework to calculate forbidden transitions, whose contribution which we show to be non-negligible. Conclusions: Forbidden transitions can be expected to contribute sizeably to the reaction strength at typical low-energy kinematics, such as DAR neutrinos. Modeling and Monte Carlo simulations need to take all due care to account for the influence of their contributions.