[Paper Review] Charged Current Coherent Pion Production in Neutrino Scattering

Paul Martins|arXiv (Cornell University)|Apr 30, 2016

Particle physics theoretical and experimental studies7 references3 citations

TL;DR

This paper compares three models of charged current coherent pion production in neutrino scattering—Rein-Sehgal and Berger-Sehgal (PCAC-based) and Alvarez-Ruso et al. (microscopic)—using experimental data from K2K, SciBooNE, T2K, MINERvA, and ArgoNEUT. It finds that the Rein-Sehgal model overestimates cross-sections, while the Berger-Sehgal and Alvarez-Ruso models show better agreement with data, especially at low neutrino energies below 3 GeV.

ABSTRACT

We summarise here the main differences of three models of neutrino-induced coherent pion production, namely the Rein-Sehgal and Berger-Sehgal models based on the Partially Conserved Axial Current theorem and the Alvarez-Ruso extit{et al.} model which is using a microscopic approach. Their predictions in the event generators are compared against recent experimental measurements for a neutrino energy from 0.5 to 20 GeV.

Motivation & Objective

• To evaluate and compare the predictions of three theoretical models for charged current coherent pion production in neutrino-nucleus scattering.
• To assess the impact of different pion-nucleus cross-section parametrizations on event generator predictions (NEUT and GENIE).
• To test model validity against recent experimental measurements from K2K, SciBooNE, T2K, MINERvA, and ArgoNEUT across neutrino energies from 0.5 to 20 GeV.
• To resolve discrepancies between event generators (NEUT vs. GENIE) in modeling coherent pion production.
• To determine whether charged current coherent pion production occurs at neutrino energies below 3 GeV, given conflicting prior results.

Proposed method

• Uses the Partially Conserved Axial Current (PCAC) theorem to relate neutrino coherent pion production to pion-nucleus scattering amplitudes.
• Applies the optical theorem in the Rein-Sehgal model to express pion-nucleus differential cross-sections in terms of total and inelastic pion-nucleon cross-sections.
• Employs a dipole propagator to extend the PCAC-based formalism beyond the forward limit (Q² = 0).
• Incorporates phase space corrections for lepton mass in charged current processes within PCAC models.
• Uses a microscopic approach in the Alvarez-Ruso et al. model that sums amplitudes coherently at the neutrino-nucleon level, including Pauli blocking and absorption effects.
• Compares model predictions against experimental data using event generators NEUT and GENIE, with consistent implementation of scattering data and phase space integration.

Experimental results

Research questions

• RQ1 How do the Rein-Sehgal, Berger-Sehgal, and Alvarez-Ruso et al. models differ in their predictions for charged current coherent pion production cross-sections?
• RQ2 To what extent do the NEUT and GENIE event generators reproduce the same predictions for these models, and what causes discrepancies?
• RQ3 Which model best describes the T2K, K2K, SciBooNE, MINERvA, and ArgoNEUT experimental measurements across the 0.5–20 GeV neutrino energy range?
• RQ4 Does the data support the existence of charged current coherent pion production at neutrino energies below 3 GeV?
• RQ5 Why does the Rein-Sehgal model overpredict the cross-section compared to experimental results, particularly in the low-energy regime?

Key findings

• The Rein-Sehgal model overestimates the total and differential coherent pion cross-sections in both NEUT and GENIE generators, especially in the 0–1 GeV pion energy range.
• The Berger-Sehgal model shows better agreement with K2K, SciBooNE, and T2K data, particularly at low neutrino energies below 3 GeV.
• The Alvarez-Ruso et al. microscopic model is consistent with experimental limits from K2K and SciBooNE and shows good agreement with T2K data, supporting its validity below 3 GeV.
• For neutrino energies above 2 GeV, the MINERvA experiment's differential cross-section measurements favor the Berger-Sehgal model over the Rein-Sehgal model, especially in the low pion momentum region.
• Discrepancies between NEUT and GENIE predictions for the Rein-Sehgal model arise from differences in phase space integration, scattering amplitude ratio (r), and pion-nucleon data implementation.
• The recent T2K measurement confirms the existence of charged current coherent pion production at energies below 3 GeV, resolving prior ambiguities from K2K and SciBooNE.