Electroweak single-pion production off the nucleon: From threshold to high invariant masses.

Neutrino-induced single-pion production (SPP) provides an important contribution to neutrino-nucleus interactions, ranging from intermediate to high energies. There exists a good number of low-energy models in the literature to describe the neutrino production of pions in the region around the Delta resonance. Those models consider only lowest-order interaction terms and, therefore, fail in the high-energy region (pion-nucleon invariant masses, W 2GeV). Our goal is to develop a model for electroweak SPP off the nucleon, which is applicable to the entire energy range of interest for present and future accelerator-based neutrino-oscillation experiments. We start with the low-energy model of [E. Hernández, J. Nieves, and M. Valverde, Phys. Rev. D 76, 033005 (2007).], which includes resonant contributions and background terms derived from the pion-nucleon Lagrangian of chiral-perturbation theory [S. Scherer and M. R. Schindler, A Primer for Chiral Perturbation Theory (Springer, Berlin, 2012), p. 1.]. Then, from the background contributions, we build a high-energy model using a Regge approach. The low-and high-energy models are combined, in a phenomenological way, into a hybrid model. The hybrid model is identical to the low-energy model in the low-W region, but, for W > 2 GeV, it implements the desired high-energy behavior dictated by Regge theory. We have tested the high-energy model by comparing with one-pion production data from electron and neutrino reactions. The hybrid model is compared with electron-proton scattering data, with neutrino SPP data and with the predictions of the NuWro Monte Carlo event generator. Our model is able to provide satisfactory predictions of the electroweak one-pion production cross section from pion threshold to high W. Further investigation and more data are needed to better understand the mechanisms playing a role in the electroweak SPP process in the high-W region, in particular, those involving the axial current contributions. [ABSTRACT FROM AUTHOR]