arXiv subjects

R. González-Jiménez

Publications and source records attributed to R. González-Jiménez.

At least 19 recordsLinked to original sources

arXiv2026

Interplay between final-state nucleon distortion, nuclear transparency and intranuclear cascade models in neutrino event generators

We present an overview of the relativistic distorted-wave impulse approximation (RDWIA) for lepton-nucleus scattering, with emphasis on its use as an elementary-vertex model in event generators. In the intermediate-energy regime, neutrino-nucleus event generators typically follow a two-step scheme: an elementary neutrino-hadron interaction is first generated, and the outgoing hadrons are then propagated through the nuclear medium using an intranuclear cascade (INC) model. Using exclusive and inclusive $(e,e'p)$ and $(e,e')$ data for several nuclei, we assess how nuclear effects should be distributed between these two stages. In particular, we identify which effects should be included in the elementary-vertex description and which can be treated more effectively by the INC, while addressing the consistency required between both components. We also discuss nuclear transparency in quasielastic scattering. We show that it is directly connected to $(e,e'p)$ data below the two-nucleon knockout threshold; and depends on the full nuclear density distribution and the initial position of the nucleon, therefore, it varies substantially with the shell from which the nucleon is removed. We demonstrate that this shell dependence can be incorporated straightforwardly into the INC component of event generators.

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arXiv2026

Relativistic distorted-wave analysis of the missing-energy spectrum measured with monochromatic $ν_μ$-$^{12}$C interactions at JSNS$^{2}$

Recently, the JSNS$^2$ collaboration measured for the first time the missing-energy distribution of $^{12}$C using a monochromatic neutrino beam coming from kaon decays at rest. In this work we present the results of an analysis of this spectrum using the relativistic distorted-wave approach. A new parameterization of the spectral function for neutrons in $^{12}$C, which incorporates detailed information from $\left(e,e'p\right)$ experiments with high missing-energy resolution has been used. The role of the recoil of the residual nucleus, final-state interactions, and neutrino event generators are discussed.

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arXiv2026

Two-body current and axial form factor effects in charged-current quasielastic neutrino-nucleus scattering within the NEUT event generator

We present a charged-current quasielastic neutrino-nucleus scattering model based on an unfactorized representation of the spectral function, employing relativistic momentum distributions for bound nucleons and the relativistic distorted-wave impulse approximation with an energy-dependent relativistic potential to describe the scattered nucleon. The model incorporates two-body meson-exchange currents contributing to one-particle-one-hole final states and tests several axial form factor parametrizations, including recent LQCD and MINERvA fits. It is implemented in the NEUT event generator and benchmarked against T2K and MINERvA $ν_μ$-$^{12}$C CC0$π$ measurements. We find that two-body meson-exchange currents lead to a sizeable increase of the total cross section, arising from an enhancement of the transverse response, which is the dominant component in charged-current neutrino scattering. On the other hand, recent fits of the axial form factor predict larger values than the standard dipole form, yielding a systematic enhancement of the cross section. The LQCD+MINERvA parametrization tends to overestimate the data, while the MINERvA-only fit provides a more moderate increase. Overall, no single configuration consistently provides the best agreement with the different datasets.

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arXiv2026

Optimizing the description of the Delta region in the Ghent Hybrid model for single-pion production

Single-pion production is an important contribution to the total neutrino-nucleus interaction cross section in accelerator-based neutrino oscillation experiments. The goal of this paper is to improve the Ghent model in the Delta resonance region by incorporating as many physical constraints as possible while keeping the number of fitted parameters as low as possible. A multipole decomposition of the model is performed allowing the use of $K$-matrix theory to unitarize the background contributions. Watson's theorem is enforced by consistently modifying both the Delta and background contributions across all multipoles. Furthermore, the decay width and form factors of the Delta contribution are modified to ensure compliance with Watson's theorem, while the model is extended to include $ρ$- and $ω$-exchange diagrams. These adjustments are compared with other pion production models, as well as with CLAS pion electroproduction data on the nucleon. The results show considerable improvement in the description of the Delta peak region.

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arXiv2025

Electron-induced single-pion production to constrain the neutron structure in $^{40}$Ar. A proof of concept

We study electron-induced single-pion production as a way to constrain the neutron structure of $^{40}$Ar, information that is necessary for neutrino experiments using argon detectors. The proposed experimental signal consists in detecting in coincidence the scattered electron, a proton and a $π^-$. We performed simulations compatible with the experimental conditions of the MAMI (University of Mainz) and CLAS (Jefferson Lab) facilities. We have computed cross sections and evaluated the main backgrounds. MAMI is a three-spectrometer system with extremely good energy resolution and small acceptances. We found that, by choosing specific values of the final particle's momenta, the shell structure can be well resolved, with negligible background contributions. CLAS is a large solid angle detector with poorer energy resolution. In both cases, the background can be kept under control by performing cuts in missing energy and missing momentum; however, in CLAS, the shell structure cannot be resolved due to the energy resolution. We conclude that MAMI is particularly appropriate for the proposed experiment, whereas CLAS is better suited for other studies.

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arXiv2025

Implementation of a relativistic distorted wave impulse approximation model into the NEUT event generator

We describe the implementation of a model for charged-current quasi-elastic (CCQE) neutrino-nucleus scattering in the NEUT Monte Carlo event generator. This model employs relativistic momentum distributions obtained from mean field theory and relativistic distorted waves to describe the initial and final nucleon states. Final state interactions, both elastic and inelastic, are modelled by combining distorted waves with the NEUT intranuclear cascade, offering a more accurate representation of the interactions experienced by scattered nucleons. The model and its implementation in NEUT are described in detail and benchmarked against $ν_μ$-$^{12}$C scattering cross-section measurements from T2K and MINER$ν$A, as well as $ν_μ$-$^{40}$Ar measurements from MicroBooNE. Results, including transverse kinematic imbalance variables and scattered nucleon kinematics, show improved $χ^2$ values compared to other CCQE models in NEUT. Furthermore, the model consistently predicts lower cross sections in CCQE-dominated regions, indicating potential for further refinement, such as incorporating two-body currents or the use of more advanced nucleon axial form factors consistent with lattice QCD calculations.

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arXiv2024

Effects of two-body currents in the one-particle one-hole electromagnetic responses within a relativistic model

Longitudinal ($R_L$) and transverse ($R_T$) responses from inclusive electron scattering from carbon 12 and calcium 40 nuclei are computed within a fully relativistic and unfactorized model for the initial and final states, and one- and two-body current operators leading to the one-particle one-hole responses. We find that the two-body contributions have no effect on $R_L$ but they increase $R_T$ by up to 30%, depending on the energy and momentum transfer. Inclusive cross sections have also been computed. In this case, the increase of $R_T$ due to two-body currents will translate into an increase in the cross-sections depending on the degree of transversity of each kinematic. The comparison with carbon data is good for the responses and the cross sections. In the case of calcium, while the model compares well with the cross section data, the agreement with the responses is generally poor. However, the inconsistencies between different data sets for the separate responses in this nucleus points to uncertainties underlying the procedure to extract the responses that are not considered (or largely underestimated) in the experimental error bars. Our calculation is fully relativistic and considers within the full quantum mechanical description both the initial and final nucleon states involved in the process. We also show that it is essential to go beyond the plane-wave approach, since incorporating the distortion of the nucleons while making the initial and final states orthogonal, allows to reproduce both the shape and magnitude of the cross section data and carbon responses. The good agreement with the electron scattering experimental data supports the use of this approach to describe the analogous neutrino-induced scattering reaction.

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arXiv2024

Final-state interactions in neutrino-induced proton knockout from argon in MicroBooNE

Neutrino event generators make use of intranuclear cascade models (INCs), to predict the kinematics of hadrons produced in neutrino-nucleus interactions. We perform a consistent comparison of different INCs, by using the same set of events as input to the NEUT, NuWro, Achilles and INCL INCs. The inputs correspond to calculations of the fully differential single-proton knockout cross section, either in the distorted-wave impulse approximation (DWIA) or plane-wave impulse approximation (PWIA), both including realistic nuclear hole spectral functions. We compare the INC results to DWIA calculations with an optical potential, used extensively in the analysis of (e,e'p) experiments. We point out a systematic discrepancy between both approaches. We apply the INC results to recent MicroBooNE data. We assess the influence of the choice of spectral function, finding that large variations in realistic spectral functions are indistinguishable with present data. The data is underpredicted, with strength missing in the region where two-nucleon knockout and resonance production contribute. However, the data is underpredicted also in regions of low transverse missing momentum, where one-nucleon knockout dominates. The inclusion of the interference with two-body currents could lead to additional strength in this region.

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arXiv2024

New model comparison for semi-inclusive charged-current electron and muon neutrino scattering by $^{40}$Ar in the energy range of the MicroBooNE experiment

In this work we present a comparison of semi-inclusive muon and electron neutrino cross sections with $^{40}$Ar target measured by the MicroBooNE Collaboration with the predictions of an unfactorized model based on the relativistic distorted wave impulse approximation (RDWIA) and the SuSAv2-MEC model implemented in the neutrino event generator GENIE. The predictions based on the RDWIA approach, with a realistic description of the initial state and a phenomenological relativistic complex optical potential for the description of final state interactions, better describe the measured cross sections than GENIE-SuSAv2 and RDWIA with a purely real potential.

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arXiv2023

Towards a more complete description of nucleon distortion in lepton-induced single-pion production at low-$Q^2$

Theoretical predictions for lepton-induced single-pion production (SPP) on $^{12}$C are revisited in order to assess the effect of different treatments of the current operator. On one hand we have the asymptotic approximation, which consists in replacing the particle four-vectors that enter in the operator by their asymptotic values, i.e., their values out of the nucleus. On the other hand we have the full calculation, which is a more accurate approach to the problem. We also compare with results in which the final nucleon is described by a relativistic plane wave, to rate the effect of the nucleon distortion. The study is performed for several lepton kinematics, reproducing inclusive and semi-inclusive cross sections belonging to the low-$Q^2$ region (between 0.05 and 1 GeV$^2$), which is of special interest in charged-current (CC) neutrino-nucleus 1$π$ production. Inclusive electron results are compared with experimental data. We find non-trivial corrections comparable in size with the effect of the nucleon distortion, namely, corrections up to 6\%, either increasing or diminishing the asymptotic prediction, and a shift of the distributions towards higher energy transfer. For the semi-inclusive cross sections, we observe the correction to be prominent mainly at low values of the outgoing nucleon kinetic energy. Finally, for CC neutrino-induced 1$π^+$ production, we find a reduction at low-$Q^2$ with respect to both the plane-wave approach and the asymptotic case.

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arXiv2023

Relativistic two-body currents for one-nucleon knockout in electron-nucleus scattering

We present a detailed study of the contribution from two-body currents to the one-nucleon knockout process induced by electromagnetic interaction. The framework is a relativistic mean-field model (RMF) in which bound and scattering nucleons are consistently described as solutions of Dirac equation with potentials. We show results obtained with the most general expression of the two-body operator, in which the intermediate nucleons are described by relativistic mean-field bound states; then, we propose two approximations consisting in describing the intermediate states as nucleons in a relativistic Fermi gas, preserving the complexity and consistency in the initial and final states. These approximations simplify the calculations considerably, allowing us to provide outcomes in a reasonable computational time. The results obtained under these approximations are validated by comparing with those from the full model. Additionally, the theoretical predictions are compared with experimental data of the longitudinal and transverse responses of carbon 12. The agreement with data is outstanding for the longitudinal response, where the contribution from the two-body operator is negligible. In the transverse sector, the two-body current increases the response from 30 to 15%, depending on the approximations and kinematics, in general, improving the agreement with data.

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arXiv2022

Final state interactions in semi-inclusive neutrino-nucleus scattering: Application to T2K and MINER$ν$A experiments

We present a complete comparison of semi-inclusive $ν_μ$-$^{12}$C cross-section measurements by T2K and MINER$ν$A collaborations with the predictions from the SuSAv2-MEC model implemented in the neutrino-nucleus event generator GENIE and an unfactorized approach based on the relativistic distorted wave impulse approximation (RDWIA). Results, that include cross sections as function of the final muon and proton kinematics and correlations between both, show that the agreement with data obtained by the RDWIA approach, that accounts for final-state interactions, matches or improves GENIE-SuSAv2 predictions for very forward angles where scaling violations are relevant.

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arXiv2021

Neutrino energy reconstruction from semi-inclusive samples

We study neutrino-nucleus charged-current reactions on finite nuclei for the situation in which an outgoing muon and a proton are detected in coincidence, i.e., we focus on semi-inclusive cross sections. We limit our attention to one-body current interactions (quasielastic scattering) and assess the impact of different nuclear effects in the determination of the neutrino energy. We identify the regions in phase space where the neutrino energy can be reconstructed relatively well, and study whether the cross section in those regions is significant. Our results indicate that it is possible to filter more than 50% of all events according to the muon and proton kinematics, so that for the DUNE and T2K fluxes the neutrino energy can be determined with an uncertainty of less than 1% and 3%, respectively. Furthermore, we find that the reconstructed neutrino energy does not depend strongly on how one treats the final-state interactions and is not much affected by the description of the initial state. On the other hand, the estimations of the uncertainty on the neutrino energy show important sensitivity to the modeling of the initial state.

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arXiv2020

Angular distributions in Monte Carlo event generation of weak single-pion production

One of the substantial sources of systematic errors in neutrino oscillation experiments that utilize neutrinos from accelerator sources stems from a lack of precision in modeling single-pion production (SPP). Oscillation analyses rely on Monte Carlo event generators (MC), providing theoretical predictions of neutrino interactions on nuclear targets. Pions produced in these processes provide a significant fraction of oscillation signal and background on both elementary scattering and detector simulation levels. Thus, it is of critical importance to develop techniques that will allow us to accommodate state-of-the-art theoretical models describing SPP into MCs. In this work, we investigate various algorithms to implement single-pion production models in Monte Carlo event generators. Based on comparison studies, we propose a novel implementation strategy that combines satisfactory efficiency with high precision in reproducing details of theoretical models predictions, including pion angular distributions. The proposed implementation is model-independent, thereby providing a framework that can include any model for SPP. We have tested the new algorithm with the Ghent Low Energy Model for single-pion production implemented in the NuWro Monte Carlo event generator.

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arXiv2020

Electron- versus neutrino-nucleus scattering

We illustrate the connection between electron and neutrino scattering off nuclei and show how the former process can be used to constrain the description of the latter. After reviewing some of the nuclear models commonly used to study lepton-nucleus reactions, we describe in detail the SuSAv2 model and show how its predictions compare with the available electron- and neutrino-scattering data over the kinematical range going from the quasi-elastic peak to pion-production and highly inelastic scattering.

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arXiv2020

Modeling neutrino-nucleus interaction at intermediate energies

We present the current status of the research activities of the Ghent group on neutrino-nucleus interactions. These consist in the modeling of some of the relevant neutrino-nucleus reaction channels at intermediate energies: low-energy nuclear excitations, quasielastic scattering, two-nucleon knockout processes and single-pion production. The low-energy nuclear excitations and the quasielastic peak are described using a Hartree-Fock-CRPA (continuum random phase approximation) model that takes into account nuclear long-range correlations as well as the distortion of the outgoing nucleon wave function. We include two-body current mechanisms through short-range correlations and meson-exchange currents. Their influence on one- and two-nucleon knockout responses is computed. Bound and outgoing nucleons are treated within the same mean-field framework. Finally, for modeling of the neutrino-induced single-pion production, we use a low-energy model that contains resonances and the background contributions required by chiral symmetry. This low-energy model is combined with a Regge approach into a Hybrid model, which allows us to make predictions beyond the resonance region.

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arXiv2020

Constraints in modeling the quasielastic response in inclusive lepton-nucleus scattering

We show that the quasielastic (QE) response calculated with the SuSAv2 (superscaling approach) model, that relies on the scaling phenomenon observed in the analysis of (e,e') data and on the relativistic mean-field theory, is very similar to that from a relativistic distorted wave impulse approximation model when only the real part of the optical potentials is employed. The coincidence between the results from these two completely independent approaches, which satisfactorily agree with the inclusive data, reinforces the reliability of the quasielastic predictions stemming from both models and sets constraints for the QE response. We also study the low energy and momentum transfer region of the inclusive response by confronting the results of the relativistic mean-field model with those of the Hartree-Fock continuum random-phase approximation model, which accounts for nuclear long-range correlations. Finally, we present a comparison of our results with the recent JLab (e,e') data for argon, titanium and carbon, finding good agreement with the three data sets.

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arXiv2019

Mean field and two-body nuclear effects in inclusive electron scattering on argon, carbon and titanium: the superscaling approach

We compare the predictions of the SuSAv2 model including two-particle two-hole meson-exchange currents with the recent JLab data for inclusive electron scattering on three different targets (C, Ar and Ti). The agreement is very good over the full energy spectrum, with some discrepancy seen only in the deep inelastic region. The 2p2h response, peaked in the dip region between the quasielastic and $Δ$-resonance peak, is essential to reproduce the data. We also analyze the $k_F$ (Fermi momentum) dependence of the data in terms of scaling of second kind, showing that the 2p2h response scales very differently from the quasielastic one, in full accord with what is predicted by the model. The results represent a valuable test of the applicability of the model to neutrino scattering processes on different nuclei.

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