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

Abstract

Background: 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 neutrinoproduction 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 2 GeV).Purpose: 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.Method: We start with the low-energy model of Ref.[1], which includes resonant contributions and background terms derived from the pion-nucleon Lagrangian of chiral-perturbation theory [2]. Then, from the background contributions, we build a high-energy model using a Regge approach. The low-and highenergy models are combined, in a phenomenological way, into a hybrid model. Results: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. Conclusions: 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.

Nuclear effects in electron-nucleus and neutrino-nucleus scattering within a relativistic quantum mechanical framework

“…with V the nuclear volume and C the coupling constant of the hadronic vertex, defined in Ref. [30]. All along this work, the bound state wave function ψ mj κ (r), labeled with the quantum numbers κ and m j [32], is always computed in the same way, i.e., within the RMF model [21,24].…”

Angular distributions in electroweak pion production off nucleons: Odd parity hadron terms, strong relative phases, and model dependence

“…This is done to minimize the effect of higher order contributions in the chiral expansion not taken into account in the evaluation of the nonresonant background within the HNV model and, also, the possible unphysical behavior of the ∆ amplitudes far from the ∆ peak that would affect the HNV model (this unphysical behavior is discussed in Ref. [34]). Besides, below this W πN cut, contributions from higher mass resonances, not taken into account in the HNV model, should be negligible.…”

Neutral-current weak pion production off the nucleon in covariant chiral perturbation theory

“…Weak single pion production off the nucleon has been extensively studied at intermediate energies with various phenomenological models. Models accounting for the ∆(1232) resonance and higher nucleon excitations have been developed [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], with some studies specifically addressing the NC case [21,22]. In addition to nucleon excitation, most of these models incorporate non-resonant amplitudes with form factors in the vertices.…”