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| Rein–Sehgal | |
|---|---|
| Name | Rein–Sehgal model |
| Year | 1981 |
| Authors | David Rein; Lawrence M. Sehgal |
| Field | Particle physics; Neutrino physics |
| Topics | Resonance (particle physics) production; Pion production; Weak interaction models |
| Related | Adler model; Feynman diagram; PCAC; Delta resonance; Quark model |
Rein–Sehgal
The Rein–Sehgal model is a phenomenological model for baryon resonance–mediated meson production in weak interactions, developed to describe single-pion and multi-pion production induced by neutrino and antineutrino scattering. It integrates inputs from hadronic spectroscopy, current algebra, and resonance phenomenology to provide cross-section predictions used by experimental collaborations and event generators. The model has been influential for analyses at facilities such as K2K, MINOS, T2K, MicroBooNE, and NOvA and remains a reference against approaches based on chiral effective field theory and lattice Quantum chromodynamics.
The Rein–Sehgal model originated in a 1981 paper by David Rein and Lawrence M. Sehgal responding to needs from CERN bubble-chamber experiments and emerging proton accelerator neutrino beams at Brookhaven National Laboratory and Fermilab. Influences cited in its development include the Feynman–Gell-Mann current algebra ideas, the partially conserved axial current (PCAC) hypothesis promoted by Stephen Adler, and the baryon resonance cataloging of the Particle Data Group. Subsequent iterations and implementations were driven by requirements of the Super-Kamiokande atmospheric-neutrino programme, the MiniBooNE anomaly studies, and simulation needs within the GENIE and NEUT event generators. Collaborations such as T2K collaboration and MiniBooNE collaboration adapted the model parameters to fit data from bubble chamber archives and modern detector results.
The model treats weak single-pion production as dominated by intermediate baryon resonances listed by the Particle Data Group such as the Delta(1232), N(1440), N(1520), and higher states. Vector current contributions are connected to electromagnetic resonance transition form factors constrained by electron scattering and photo-production data from facilities like Jefferson Lab and SLAC, invoking vector-meson-dominance considerations linked to rho meson phenomenology. Axial current form factors are modeled using PCAC and pion-pole dominance with axial masses motivated by fits to Bubble chamber measurements at ANL and BNL. The Rein–Sehgal approach combines relativistic Breit–Wigner parametrizations for resonance propagators with isospin Clebsch–Gordan factors associated with SU(2) multiplets and helicity amplitudes informed by quark model expectations from Isgur–Karl model–style analyses.
Rein–Sehgal expresses the differential cross section dσ/dQ^2dW in terms of resonance contributions summed over spin-parity states, where Q^2 denotes the four-momentum transfer squared and W the hadronic invariant mass. Resonance amplitudes use relativistic Breit–Wigner forms similar to those in Höhler-type analyses, with width Γ(W) and mass M_R parameters taken from the Particle Data Group listings. Vector transition form factors F_V(Q^2) are linked via conserved vector current (CVC) to electromagnetic helicity amplitudes A_1/2 and A_3/2 measured in electron scattering experiments at DESY and Jefferson Lab. Axial form factors F_A(Q^2) adopt dipole shapes with axial mass M_A values constrained by deuterium bubble-chamber fits from ANL and BNL. Interference between resonances and nonresonant backgrounds is often neglected or modeled phenomenologically, and isospin decomposition uses standard Clebsch–Gordan coefficients to convert resonance couplings to specific pion charge channels.
The model has been implemented in neutrino event generators used by long-baseline oscillation experiments like NOvA and T2K, short-baseline experiments such as MicroBooNE and MiniBooNE, and atmospheric analyses at Super-Kamiokande. It provides predictions for charged-current single-pion (CC1π) and neutral-current single-pion (NC1π) channels, informs background estimates for charged-current quasi-elastic (CCQE) selections, and supplies inputs for detector simulation chains at CNGS and NuMI beams. Rein–Sehgal outputs feed flux-integrated cross sections used in global fits performed by collaborations like NuFit and influence sensitivity projections for CP violation searches in Hyper-Kamiokande and DUNE.
Comparisons between Rein–Sehgal predictions and data have been performed using historical bubble-chamber datasets from ANL and BNL, modern measurements from MINERvA, T2K near detector complex (including ND280), and inclusive pion-production results from MiniBooNE. Discrepancies have been noted in absolute cross-section normalizations, Q^2 distributions, and angular spectra, leading to retuning of axial mass parameters and ad hoc modifications to nonresonant backgrounds. Validation efforts have also involved comparisons with electron-scattering–based models validated at Jefferson Lab and with theoretical calculations from chiral perturbation theory near threshold and lattice Quantum chromodynamics for form-factor inputs.
Extensions include implementations with explicit nonresonant background terms informed by Sato–Lee model and hybrid schemes combining Rein–Sehgal resonance sums with chiral low-energy amplitudes. Modifications introduced by later authors address shortcomings such as the treatment of lepton mass effects for tau neutrino channels, refined kinematic thresholds, and updated resonance branching ratios from successive Particle Data Group reviews. Criticisms focus on neglect of final-state interactions treated in transport models like GiBUU, oversimplified interference between resonances and background, and limited consistency with chiral-symmetry constraints emphasized by Bernard, Kaiser, Meißner-type analyses. Despite limitations, the model remains widely used for practical simulation, benchmarking, and historical continuity in neutrino-scattering studies.
Category:Neutrino interaction models