Reliable models of neutrino pion production on nuclei
In plain words
In the few-GeV range many neutrino collisions make a pion, often through a short-lived excited nucleon called the Delta. Measurements from different experiments and the models used to describe them do not agree, especially for slow pions and small momentum transfers.
Precise statement
Construct a model of charged- and neutral-current single-pion production on 12C, 16O and 40Ar for $E_{\nu} = 0.5\ \text{to}\ 5\ \mathrm{GeV}$ that simultaneously reproduces MiniBooNE, MINERvA and T2K pion kinematic distributions, including the low-$Q^2$ suppression and the pion absorption and charge exchange in the nucleus. The answer must identify the physics (in-medium $\Delta$ properties, nonresonant background, final-state interactions, flux normalization) responsible for the inter-experiment tension.
What would settle it
A single model, constrained by pion electroproduction and hydrogen or deuterium neutrino data, that fits all nuclear-target pion data within quoted uncertainties.