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We present our description of neutrino induced charged current quasielastic scattering (CCQE) in nuclei at energies relevant for the MiniBooNE experiment. In our framework, the nucleons, with initial momentum distributions according to the Local Fermi Gas model, move in a density- and momentum-dependent mean field potential. The broadening of the outgoing nucleons due to nucleon-nucleon interactions is taken into account by spectral functions. Long range (RPA) correlations renormalizing the electroweak strength in the medium are also incorporated. The background from resonance excitation events that do not lead to pions in the final state is also predicted by propagating the outgoing hadrons with the Giessen semiclassical BUU model in coupled channels (GiBUU). We achieve a good description of the shape of the CCQE Q2 distribution extracted from data by MiniBooNE, thanks to the inclusion of RPA correlations, but underestimate the integrated cross section when the standard value of MA = 1 GeV is used. Possible reasons for this mismatch are discussed.
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Neutrino oscillation probabilities, which are being measured in long-baseline experiments, depend on neutrino energy. The energy in a neutrino beam, however, is broadly smeared so that the neutrino energy in a particular event is not directly known, but must be reconstructed from final state properties. In this paper we investigate the contributions from different reaction mechanisms on the energy-reconstruction method widely used in long-baseline neutrino experiments. Difference between the true-QE and QE-like cross sections in MiniBooNE experiment is investigated in details. It is shown, that fake QE-like events lead to significant distortions in neutrino energy reconstruction. Flux-folded and unfolded cross sections for QE-like scattering are calculated as functions of both true and reconstructed energies. Flux-folded momentum transfer distributions are calculated as functions of both true and reconstructed momentum transfer. Distributions versus reconstructed values are compared with the experimental data. Also presented are the conditional probability densities of finding a true energy for a given reconstructed energy. It is shown, how the energy reconstruction procedure influences the measurement of oscillation parameters in T2K experiment. For the reconstruction procedure based on quasielastic (QE) kinematics, all other reaction channels beside true-QE scattering show a shift of the reconstructed energy towards lower values as compared to the true energy. On average in the MiniBooNE and T2K experiments the shift is 100 - 200 MeV and depends on energy. The oscillation signals are similarly affected. These uncertainties may limit the extraction of a CP violating phase from an oscillation result.
[Background] Meticulous modeling of neutrino-nucleus interactions is essential to achieve the unprecedented precision goals of present and future accelerator-based neutrino-oscillation experiments. [Purpose] Confront our calculations of charged-current quasielastic cross section with the measurements of MiniBooNE and T2K, and to quantitatively investigate the role of nuclear-structure effects, in particular, low-energy nuclear excitations in forward muon scattering. [Method] The model takes the mean-field (MF) approach as the starting point, and solves Hartree-Fock (HF) equations using a Skyrme (SkE2) nucleon-nucleon interaction. Long-range nuclear correlations are taken into account by means of the continuum random-phase approximation (CRPA) framework. [Results] We present our calculations on flux-folded double differential, and flux-unfolded total cross sections off $^{12}$C and compare them with MiniBooNE and (off-axis) T2K measurements. We discuss the importance of low-energy nuclear excitations for the forward bins. [Conclusions] The CRPA predictions describe the gross features of the measured cross sections. They underpredict the data (more in the neutrino than in the antineutrino case) because of the absence of processes beyond pure quasielastic scattering in our model. At very forward muon scattering, low-energy nuclear excitations ($omega < $ 50 MeV) account for nearly 50% of the flux-folded cross section.
We investigate charged and neutral current neutrino induced incoherent pion production off nuclei at MiniBooNE and K2K energies within the GiBUU model. We assume impulse approximation and treat the nucleus as a local Fermi gas of nucleons bound in a mean-field potential. In-medium spectral functions are also taken into account. The outcome of the initial neutrino nucleon reaction undergoes complex hadronic final state interactions. We present results for neutral current pi^0 and charged current pi^+ production and compare to MiniBooNE and K2K data.
We apply the GiBUU model to questions relevant for current and future neutrino long-baseline experiments, we address in particular the relevance of charged-current reactions for neutrino disappearance experiments. A correct identification of charged-current quasielastic (CCQE) events - which is the signal channel in oscillation experiments - is relevant for the neutrino energy reconstruction and thus for the oscillation result. We show that about 20% of the quasielastic cross section is misidentified in present-day experiments and has to be corrected for by means of event generators. Furthermore, we show that also a significant part of 1pi+ (> 40%) events is misidentified as CCQE mainly caused by the pion absorption in the nucleus. We also discuss the dependence of both of these numbers on experimental detection thresholds. We further investigate the influence of final-state interactions on the neutrino energy reconstruction.
We present a model for electron- and neutrino-scattering off nucleons and nuclei focussing on the quasielastic and resonance region. The lepton-nucleon reaction is described within a relativistic formalism that includes, besides quasielastic scattering, the excitation of 13 N* and Delta resonances and a non-resonant single-pion background. Recent electron-scattering data is used for the state-of-the-art parametrizations of the vector form factors; the axial couplings are determined via PCAC and, in the case of the Delta resonance, the axial form factor is refitted using neutrino-scattering data. Scattering off nuclei is treated within the GiBUU framework that takes into account various nuclear effects: the local density approximation for the nuclear ground state, mean-field potentials and in-medium spectral functions. Results for inclusive scattering off Oxygen are presented and, in the case of electron-induced reactions, compared to experimental data and other models.
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