arXiv subjects

Raúl González-Jiménez

Publications and source records attributed to Raúl González-Jiménez.

15 recordsLinked to original sources

arXiv2026

Electromagnetic responses induced by one- and two-body nuclear currents in inclusive electron-nucleus scattering

The longitudinal and transverse nuclear response functions encode information about the electromagnetic behavior of the nuclear target probed in inclusive electron-nucleus scattering. We present a microscopic calculation based on an independent-particle model, where a non-relativistic nuclear mean-field potential governs both the initial and final hadronic states of the interaction. We add dynamically generated short-range nucleon-nucleon correlations (SRCs), as well as meson-exchange currents (MECs) derived from one-pion exchange and intermediate $Δ$-resonance excitation. We evaluate the contributions from one- and two-nucleon knock-out reactions to nuclear responses in inclusive electron scattering from $^{12}\mathrm{C}$ in the quasielastic and dip regions. We demonstrate that for quasielastic kinematics, SRCs quench both nuclear responses, while the MECs enhance the transverse signal, substantially improving the predicted transverse-to-longitudinal ratio. In the dip region between the quasielastic and the $Δ$-resonance peaks, we find that the observed excess of transverse strength originates mainly from explicit two-nucleon knock-out following a $Δ$-resonance excitation.

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arXiv2026

Lectures on lepton-nucleus quasielastic scattering with relativistic models

In these notes, basic concepts and necessary formulas for the modeling of elastic lepton-nucleon and quasielastic lepton-nucleus scattering using relativistic models are discussed. Certain theoretical developments are presented in meticulous detail, particularly those rarely found in papers or standard textbooks. In order to highlight the discrepancies between models and evaluate the impact of various nuclear effects, theoretical predictions are compared with inclusive electron scattering data. These notes are designed for Master's or PhD students embarking on their research in the field of neutrino-nucleus interactions at intermediate energies (ranging from several hundred MeV to a few GeV). They are intended to serve as a supplemental guide, never as a substitute for traditional textbooks on Scattering Theory and Quantum Field Theory. Currently, these notes are included in the course `Relativistic Quantum Theory: Nuclear Processes', which is integrated into both the Interuniversity Master in Nuclear Physics (https://master.us.es/fisicanuclear/index.php/) and the Erasmus Mundus Joint Master Degree in Nuclear Physics (https://www.emm-nucphys.eu/en), with the University of Seville as one of the partner institutions. Previously, this material was part of the course `Weak Interactions', within the same Master's programs.

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arXiv2026

Charged-Current Neutrino-Induced Single-Pion Production in the Superscaling Approach and Relativistic Distorted-Wave Impulse Approximation

In this work, we present a detailed comparison of the SuSAv2 (SuperScaling Approach version 2) and RDWIA (Relativistic Distorted-Wave Impulse Approximation) models with measurements of charged-current neutrino-induced single-pion production from different experiments (T2K, MINERvA and MiniBooNE), studying the differences between the two theoretical descriptions. The neutrino energy range in these experiments spans from hundreds of MeV to roughly 20 GeV, and the nuclear targets are mainly composed of $^{12}$C. The SuSAv2 model uses the single-nucleon inelastic structure functions from the ANL-Osaka DCC model, which allows for a separation of pion production channels, distinguishing between the $π^+$, $π^-$ and $π^0$ final states. In the RDWIA approach, the Hybrid model developed by the Ghent group is used for the description of the boson-pion-nucleon vertex.

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arXiv2025

Factorized distorted wave calculations for electron, neutrino, and BSM processes

We point out that, under certain conditions, the nuclear currents that couple to vector bosons can be written as the trace of the product of two matrices. One contains `nucleon dynamics', e.g. form factors, the other contains the overlaps of nuclear wavefunctions. This factorized form may always be obtained and viewed as a `local' approximation, in which particle four-momenta that enter in the transition operator are fixed to their asymptotic values. We write the overlap matrix in a general form in terms of Dirac matrices. The current with arbitrary couplings to the nucleon can then be evaluated using standard trace identities. We show that this encompasses non-relativistic models as well. We have tabulated overlaps obtained in the relativistic distorted-wave impulse approximation, which can be used to compute the single-nucleon knockout cross section. We give a self-contained overview of the formulae. We discuss some properties of the overlap matrices which may be derived from general principles, and highlight differences with the commonly used plane-wave impulse approximation. The factorized form is attractive for (neutrino) event generators: it abstracts away the nuclear model and allows to easily modify couplings to the nucleon. This allows to consistently treat electron, neutrino and beyond Standard Model (BSM) processes.

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arXiv2024

The Ghent Hybrid Model in NuWro: a new neutrino single-pion production model in the GeV regime

Neutrino-induced single-pion production constitutes an essential interaction channel in modern neutrino oscillation experiments, with its products building up a significant fraction of the observable hadronic final states. Frameworks of oscillation analyses strongly rely on Monte Carlo neutrino event generators, which provide theoretical predictions of neutrino interactions on nuclear targets. Thus, it is crucial to integrate state-of-the-art single-pion production models with Monte Carlo simulations to prepare for the upcoming systematics-dominated landscape of neutrino measurements. In this work, we present the implementation of the Ghent Hybrid model for neutrino-induced single-pion production in the NuWro Monte Carlo event generator. The interaction dynamics includes coherently-added contributions from nucleon resonances and a non-resonant background, merged into the pythia branching predictions in the deep-inelastic regime, as instrumented by NuWro. This neutrino-nucleon interaction model is fully incorporated into the nuclear framework of the generator, allowing it to account for the influence of both initial- and final-state nuclear medium effects. We compare the predictions of this integrated implementation with recent pion production data from accelerator-based neutrino experiments. The results of the novel model show improved agreement of the generator predictions with the data and point to the significance of the refined treatment of the description of pion-production processes beyond the $Δ$ region.

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arXiv2023

From inclusive to semi-inclusive one-nucleon knockout in neutrino event generators

In neutrino event generators, for models for neutrino and electron scattering only inclusive cross sections are implemented. When these models are used to describe a semi-inclusive cross section, the event generator attaches the hadron variables based on some assumptions. In this work we compare the nucleon kinematics given by the method used in the GENIE event generator, e.g. in the implementation of the SuSAv2 model, to a fully unfactorized calculation using the relativistic distorted wave impulse approximation (RDWIA). We focus on kinematics relevant to the $e4ν$ analysis and show that observables obtained with RDWIA differ significantly from those of the approximate method used in GENIE, the latter should be considered unrealistic.

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arXiv2022

Assessing the theory-data tension in neutrino-induced charged pion production: the effect of final-state nucleon distortion

Pion production on nuclei constitutes a significant part of the total cross section in experiments involving few-GeV neutrinos. Combined analyses of data on deuterium and heavier nuclei points to tensions between the bubble chamber data and the data of the MINER$ν$A experiment, which are often ascribed to unspecified nuclear effects. To understand the origin of these tensions, a microscopic quantum mechanical framework is needed to compute nuclear matrix elements. We use the local approximation to the relativistic distorted wave impulse approximation (RDWIA) to assess the role of final-state nucleon distortion. To perform this comparison under conditions relevant to neutrino experiments, we compute cross sections for the MINER$ν$A and T2K charged pion production datasets. The inclusion of nucleon distortion leads to a reduction of the cross section up to 10\%, but to no significant change in shape of the flux-averaged cross sections. Results with and without distortion compare favorably to experimental data, with the exception of the low-$Q^2$ MINER$ν$A $π^+$ data. We point out that hydrogen target data from BEBC is also overpredicted at low-$Q^2$, and that the discrepancy is similar in shape and magnitude to what is found in comparison to MINER$ν$A data. Including nucleon distortion alone cannot explain the overprediction of low-$Q^2$ cross sections measured by MINER$ν$A. The similar overprediction of BEBC data on hydrogen means that it is impossible to ascribe this discrepancy solely to a nuclear effect. Axial couplings and their $Q^2$ dependence should ideally be derived from more precise data on hydrogen and deuterium.

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arXiv2022

Benchmarking intra-nuclear cascade models for neutrino scattering with relativistic optical potentials

The description of final-state interactions (FSI) in the large phase space probed in neutrino experiments poses a great challenge. In neutrino experiments, which operate under semi-inclusive conditions, cascade models are commonly used for this task, while under exclusive conditions FSI can be treated with relativistic optical potentials (ROP). We formulate conditions under which the ROP approach and cascade model can be directly compared. We feed the NEUT cascade with events from a relativistic distorted-wave impulse approximation calculation that uses the real part of an optical potential. Cuts on the missing energy of the resulting events are applied to define a set of events that can be directly compared to RDWIA calculations with the full optical potential. The NEUT cascade and ROP agree for proton kinetic energies $T_p > 150$ MeV for carbon, oxygen and calcium nuclei when a realistic nuclear density is used to introduce events in the cascade. For $T_p < 100$ MeV the ROP and NEUT cross sections differ in shape and differences in magnitude are larger than 50 \%. Single transverse variables allow to distinguish different approaches to FSI, but due to a large non-QE contribution the comparison to T2K data does not give an unambiguous view of FSI. We discuss electron scattering and argue that with a cut in missing energy FSI can be studied with minimal confounding factors in e.g. $e4ν$. The agreement of the ROP and NEUT for T2K conditions lends confidence to these models as a tool in oscillation analyses for sufficiently large nucleon kinetic energies. These results urge for caution when a cascade model is applied for small nucleon energies. The assessment of model assumptions relevant to this region are strongly encouraged. This paper provides novel constraints on cascade models from proton-nucleus scattering that can be easily applied to other neutrino event generators.

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arXiv2019

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

We study the impact of the description of the knockout nucleon wave function on electron- and neutrino-induced quasielastic and single-pion production cross sections. We work in a fully relativistic and quantum mechanical framework, where the relativistic mean-field model is used to describe the target nucleus. The focus is on Pauli blocking and the distortion of the final nucleon, these two nuclear effects are separated and analyzed in detail. We find that a proper quantum mechanical treatment of these effects is crucial to provide the correct magnitude and shape of the inclusive cross section. Also, this seems to be key to predict the right ratio of muon- to electron-neutrino cross sections at very forward scattering angles.

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arXiv2019

Neutrino-induced single-pion production: Kinematics and Cross Section

In the energy range of present and future accelerator-based neutrino-oscillation experiments, single-pion production (SPP) is one of the main contributions to the neutrino-nucleus scattering cross section. For these neutrino energies, ranging from several hundreds of MeV to a few GeV, the SPP on the nucleus is usually described by the reaction in which the incoming lepton couples to one bound nucleon in the nucleus, producing a pion and the knock-out nucleon, along with the residual system and the scattered lepton in the final state. Here, the kinematics and cross section formula for this process are discussed, although the formalism can be applied to other $2\rightarrow4$ processes.

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arXiv2019

Electron versus muon neutrino induced cross sections in charged current quasi-elastic processes

Differences between $ν_e$ and $ν_μ$ quasielastic cross sections are essential in neutrino oscillation analyses and CP violation searches for experiments such as DUNE and T2HK. The ratio of these is however poorly known experimentally and for certain kinematic regions theoretical models give contradictory answers. We use two independent mean-field based models to investigate this ratio using $^{40}$Ar and $^{12}$C targets. We demonstrate that a proper treatment of the final nucleon's wave function confirms the dominance of $ν_μ$ over $ν_e$ induced cross sections at forward lepton scattering.

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arXiv2018

Mean field approach to reconstructed neutrino energy distributions in accelerator-based experiments

The reconstruction of the neutrino energy is crucial in oscillation experiments that use interactions with nuclei to detect the neutrino. The common reconstruction procedure is based on the kinematics of the final-state lepton. The interpretation of the reconstructed energy in terms of the real neutrino energy must rely on a model for the neutrino-nucleus interaction. The Relativistic Fermi Gas (RFG) model is frequently used in these analyses. In the Hartree-Fock (HF) model for quasielastic nucleon knockout, the bound nucleon wave functions are obtained using an effective nucleon-nucleon force. The final-state wave function is constructed from continuum states in the same potential which have the correct asymptotic behavior. The Continuum Random Phase Approximation (CRPA) model extends the HF approach taking long range correlations into account in a self-consistent way. Considering only single-nucleon processes, the distributions of reconstructed neutrino energies obtained within the HF-CRPA approach are compared with the results of the RFG, an RPWIA calculation, and the RPA+np-nh model of Martini et al. We find that the distributions of reconstructed energies for a fixed incoming energy in the HF-CRPA display additional strength in the low reconstructed energy tails compared to models without elastic distortion of the outgoing nucleon. This asymmetry redistributes strength from higher to lower values of the reconstructed energy. The mean field description of the nuclear dynamics results in a reshaping of the reconstructed energy distribution that cannot be accounted for in a plane wave impulse approximation model, even by modifying ad hoc parameters such as the binding energy. In particular it is shown that in the RFG calculations there is no value of the binding energy which is able to reproduce the entire T2K $ν_μ$ oscillated spectrum as calculated in HF-CRPA.

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arXiv2018

$A$-dependence of quasielastic charged-current neutrino-nucleus cross sections

Background: 12C has been and is still widely used in neutrino-nucleus scattering and oscillation experiments. More recently, 40Ar has emerged as an important nuclear target for current and future experiments. Liquid argon time projection chambers (LArTPCs) possess various advantages in measuring electroweak neutrino-nucleus cross sections. Concurrent theoretical research is an evident necessity. Purpose: 40Ar is larger than 12C, and one expects nuclear effects to play a bigger role in reactions. We present inclusive differential and total cross section results for charged-current neutrino scattering on 40Ar and perform a comparison with 12C, 16O and 56Fe targets, to find out about the A-dependent behavior of model predictions. Method: Our model starts off with a Hartree-Fock description of the nucleus, with the nucleons interacting through a mean field generated by an effective Skyrme force. Long-range correlations are introduced by means of a continuum random phase approximation (CRPA) approach. Further methods to improve the accuracy of model predictions are also incorporated in the calculations. Results: We present calculations for 12C, 16O, 40Ar and 56Fe, showcasing differential cross sections over a broad range of kinematic values in the quasielastic regime. We furthermore show flux-folded results for 40Ar and we discuss the differences between nuclear responses. Conclusions: At low incoming energies and forward scattering we identify an enhancement in the 40Ar cross section compared to 12C, as well as in the high $ω$ (low $T_μ$ ) region across the entire studied $E_ν$ range. The contribution to the folded cross section of the reaction strength at values of $ω$ lower than 50 MeV for forward scattering is sizeable.

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arXiv2018

Modeling neutrino-induced charged pion production on water at T2K kinematics

Pion production is a significant component of the signal in accelerator-based neutrino experiments. Over the last years, the MiniBooNE, T2K and MINERvA collaborations have reported a substantial amount of data on (anti)neutrino-induced pion production on the nucleus. However, a comprehensive and consistent description of the whole data set is still missing. We aim at improving the current understanding of neutrino-induced pion production on the nucleus. To this end, the comparison of experimental data with theoretical predictions, preferably based on microscopic models, is essential to disentangle the different reaction mechanisms involved in the process. To describe single-pion production (SPP) we use a hybrid model that combines a low- and a high-energy approach. The low-energy model (LEM) contains resonances and background terms. At high invariant masses, a high-energy model based on a Regge approach is employed. The model is implemented in the nucleus using the relativistic plane wave impulse approximation (RPWIA). We present a comparison of the hybrid-RPWIA and LEM with the recent neutrino-induced charged current $1π^+$ production cross section on water reported by T2K. In order to judge the impact of final-state interactions (FSI) we confront our results with those of the NuWro Monte Carlo generator. The hybrid-RPWIA model and NuWro compare favorably to the data, albeit that FSI are not included in the former. These results complement our previous work [Phys. Rev. D 97, 013004 (2018)] where we compared the models to the MINERvA and MiniBooNE $1π^+$ data. The hybrid-RPWIA model tends to overpredict both the T2K and MINERvA data in kinematic regions where the largest suppression due to FSI is expected, and agrees remarkably well with the data in other kinematic regions. On the contrary, the MiniBooNE data is underpredicted over the whole kinematic range.

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arXiv2015

Estimate of the theoretical uncertainty of the cross sections for nucleon knockout in neutral-current neutrino-oxygen interactions

Free nucleons propagating in water are known to produce gamma rays, which form a background to the searches for diffuse supernova neutrinos and sterile neutrinos carried out with Cherenkov detectors. As a consequence, the process of nucleon knockout induced by neutral-current quasielastic interactions of atmospheric (anti)neutrinos with oxygen needs to be under control at the quantitative level in the background simulations of the ongoing and future experiments. In this paper, we provide a quantitative assessment of the uncertainty associated with the theoretical description of the nuclear cross sections, estimating it from the discrepancies between the predictions of different models.

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