arXiv subjects

Marco Martini

Publications and source records attributed to Marco Martini.

16 recordsLinked to original sources

arXiv2025

Two-particle two-hole excitations in semi-inclusive neutrino-nucleus scattering

A calculation of the two-particle two-hole contribution to the semi-inclusive $(\nu_\mu,\mu^-N)$ cross section on carbon is performed in the framework of the relativistic Fermi gas model. The process is driven by meson-exchange currents encompassing all contributions involving the exchange of a single pion and the excitation of a $\Delta$ resonance. The calculation is validated against the inclusive $(\nu_\mu,\mu^-)$ response functions already existing in the literature, and then extended for the first time to the semi-inclusive channel. Results are presented both at fixed neutrino energy and folded with the T2K neutrino flux.

nucl-th↗

arXiv2025

Fragmentation of the IAR along the chains $ \boldsymbol{N=50} $ and $ \boldsymbol{Z=50} $

We study Isobaric Analog Resonances in even-even nuclei along the $ N=50 $ isotonic chain. First, Hartree-Fock-Bogoliubov calculations, using the Gogny D1M effective interaction, have been performed to provide energies and occupation probabilities of nucleon orbitals. The Isobaric Analog Resonances are calculated with the charge exchange QRPA approach on top of then HFB calculations. Fermi transition mechanism is interpreted with the existence of collective modes in the final nucleus. The fragmentation of the Fermi Strength results from the fractional occupation of nucleon shells, a direct consequence of nuclear pairing. The theoretical Fermi transition probabilities along the isotopic chain $ Z=50 $ are also analyzed and confirm our conclusions.

nucl-th↗

arXiv2025

Implementation of the Martini-Ericson-Chanfray-Marteau RPA-based neutrino and antineutrino cross-section model in the GENIE neutrino event generator

We discuss the first implementation of the Martini-Ericson-Chanfray-Marteau random phase approximation-based (anti)neutrino cross-section model for quasielastic (1p1h) and multinucleon (2p2h and 3p3h) excitations in the widely used GENIE neutrino event generator. Validation steps are presented, in particular, through direct comparisons of GENIE cross-section output with original calculations performed by the authors of the model. Predictions for $^{12}$C, $^{16}$O, and $^{40}$Ar are compared with some available T2K and MicroBooNE experimental measurements showing a reasonable agreement.

hep-ex↗

arXiv2025

Meson-Exchange Currents in Quasielastic Charged-Current Neutrino Reactions with Single-Nucleon Knockout

The effect of meson-exchange currents on charged-current quasielastic neutrino scattering with single-nucleon emission is computed and analyzed within the relativistic Fermi gas model. This contribution arises primarily from the interference between one-body and two-body currents, where the two-body operator excites a 1p1h state in the presence of a second, spectator nucleon. The results obtained show a reduction of the vector, axial and vector-axial transverse response functions and, consequently, a decrease in the total neutrino cross section. In addition to a comparison with the non-relativistic limit, other models are also explored, such as the relativistic mean field model for nuclear matter and the superscaling analysis with relativistic effective mass, both of which yield qualitatively similar results.

hep-ph↗

arXiv2025

Interference between Meson Exchange and One-Body Currents in Quasielastic Electron Scattering

In this work, we present a detailed analysis of the interference between meson exchange currents (MEC) and one-body currents in quasielastic electron scattering, with a focus on the sign of this interference in the transverse response for one-particle emission. We prove that the interference of both the Delta and pion-in-flight currents with the one-body current is negative, leading to a partial cancellation with the seagull current. This is mathematically demonstrated within the framework of the Fermi gas model. By comparing these interferences across various independent particle models, both relativistic and non-relativistic, our results indicate that all studied models display the same behavior. This consistency suggests that the interference is negative in models that do not incorporate tensor correlations in the nuclear wave function.

nucl-th↗

arXiv2025

From QCD phenomenology to nuclear physics phenomenology: the chiral confining model

We present a theoretical framework allowing to make an explicit connection between the phenomenology of QCD, namely the properties of the gluon correlator and Wilson loops, and a particular relativistic model for the description of nuclear matter and neutron stars, the chiral confining model. Starting with the Field Correlator Method, which incorporates explicitly and simultaneously confinement and chiral symmetry breaking, we describe how to obtain the response of the composite nucleon to the nuclear scalar field, the relative role of confinement and chiral symmetry breaking in the in-medium nucleon mass evolution, generating the three-body forces needed for the saturation mechanism.

nucl-th↗

arXiv2024

Fine-Tuned 'Small' LLMs (Still) Significantly Outperform Zero-Shot Generative AI Models in Text Classification

Generative AI offers a simple, prompt-based alternative to fine-tuning smaller BERT-style LLMs for text classification tasks. This promises to eliminate the need for manually labeled training data and task-specific model training. However, it remains an open question whether tools like ChatGPT can deliver on this promise. In this paper, we show that smaller, fine-tuned LLMs (still) consistently and significantly outperform larger, zero-shot prompted models in text classification. We compare three major generative AI models (ChatGPT with GPT-3.5/GPT-4 and Claude Opus) with several fine-tuned LLMs across a diverse set of classification tasks (sentiment, approval/disapproval, emotions, party positions) and text categories (news, tweets, speeches). We find that fine-tuning with application-specific training data achieves superior performance in all cases. To make this approach more accessible to a broader audience, we provide an easy-to-use toolkit alongside this paper. Our toolkit, accompanied by non-technical step-by-step guidance, enables users to select and fine-tune BERT-like LLMs for any classification task with minimal technical and computational effort.

cs.CL↗

arXiv2024

Relativistic meson-exchange currents in semi-inclusive lepton scattering

We assess the impact of two-particle--two-hole excitations on the semi-inclusive electron scattering process (e,e'p) using a fully relativistic nuclear model calculation that precisely incorporates antisymmetrization. The calculation encompasses all contributions involving the exchange of a single pion and the excitation of a Delta resonance. Our results are compared with (e,e'p) data on carbon at kinematics where two-nucleon emission dominates. This work represents an essential step towards the microscopic computation of the two-particle--two-hole contribution to semi-inclusive neutrino reactions, crucial in the analysis of neutrino oscillation experiments.

nucl-th↗

arXiv2023

Nuclear models for inclusive lepton-nucleus scattering in the quasi-elastic region and beyond

High-precision measurements in neutrino oscillation experiments require a very accurate description of the lepton-nucleus scattering process. Several cross-section calculations are available, but important discrepancies are still present between different model predictions. For the quasi-elastic channel, dominated by one particle-one hole excitations, an overview over several nuclear models - specifically Relativistic Fermi Gas, SuperScaling Approach, Spectral Function, Hartree-Fock and Random Phase Approximation - is presented and compared with data for electron-nucleus scattering, a very important process for testing theoretical models validity, highlighting the specific features of each approach. Furthermore an ongoing microscopic calculation of the two particle-two hole excitations contribution to the electromagnetic response is presented, and some preliminary results are shown.

nucl-th↗

arXiv2023

The Interrelated Roles of Correlations in the Nuclear Equation of State and in Response Functions: Application to a Chiral Confining Theory

We study the role of short-range correlations, as well as pion and rho loops governing long-range RPA correlations, in nuclear matter properties and response functions. We use an adapted formulation of the Brueckner G-matrix approach to generate a pair correlation function satisfying the Beg--Agassi--Gal theorem, providing a natural cutoff to the loop integrals. We present results for the case of a relativistic chiral theory, including the effects of quark confinement and of the chirally broken vacuum in a version where parameters are directly connected to QCD observables or constrained by well-established hadron phenomenology. This provides a unified and coherent view of the nuclear matter equation of state and the effect of correlations on neutrino--nucleus scattering.

nucl-th↗

arXiv2019

Research and Development for Near Detector Systems Towards Long Term Evolution of Ultra-precise Long-baseline Neutrino Experiments

With the discovery of non-zero value of $θ_{13}$ mixing angle, the next generation of long-baseline neutrino (LBN) experiments offers the possibility of obtaining statistically significant samples of muon and electron neutrinos and anti-neutrinos with large oscillation effects. In this document we intend to highlight the importance of Near Detector facilities in LBN experiments to both constrain the systematic uncertainties affecting oscillation analyses but also to perform, thanks to their close location, measurements of broad benefit for LBN physics goals. A strong European contribution to these efforts is possible.

physics.ins-det↗

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.

nucl-th↗

arXiv2017

Status and challenges of neutrino cross sections

Neutrino oscillations physics entered in the precision era. In this context accelerator-based neutrino experiments need a reduction of systematic errors to the level of a few percent. Today one of the most important sources of systematic errors are the neutrino-nucleus cross sections. The status of our knowledge of these cross sections in the different open channels in the few-GeV region, i.e. the quasielastic, the pion production and the multinucleon emission, is reviewed. Special emphasis is devoted to the multinucleon emission channel, which attracted a lot of attention in the last few years. It is crucial to properly reconstruct the neutrino energy which enters the expression of the oscillation probability. This channel was not included in the generators used for the analyses of the neutrino cross sections and oscillations experiments.

hep-ph↗

arXiv2016

Neutrino-Nucleus Cross Sections for Oscillation Experiments

Neutrino oscillations physics is entered in the precision era. In this context accelerator-based neutrino experiments need a reduction of systematic errors to the level of a few percent. Today one of the most important sources of systematic errors are neutrino-nucleus cross sections which in the hundreds-MeV to few-GeV energy region are known with a precision not exceeding 20%. In this article we review the present experimental and theoretical knowledge of the neutrino-nucleus interaction physics. After introducing neutrino oscillation physics and accelerator-based neutrino experiments, we overview general aspects of the neutrino-nucleus cross sections, both theoretical and experimental views. Then we focus on these quantities in different reaction channels. We start with the quasielastic and quasielastic-like cross section, putting a special emphasis on multinucleon emission channel which attracted a lot of attention in the last few years. We review the main aspects of the different microscopic models for this channel by discussing analogies and differences among them.The discussion is always driven by a comparison with the experimental data. We then consider the one pion production channel where data-theory agreement remains very unsatisfactory. We describe how to interpret pion data, then we analyze in particular the puzzle related to the impossibility of theoretical models and Monte Carlo to simultaneously describe MiniBooNE and MINERvA experimental results. Inclusive cross sections are also discussed, as well as the comparison between the $ν_μ$ and $ν_e$ cross sections, relevant for the CP violation experiments. The impact of the nuclear effects on the reconstruction of neutrino energy and on the determination of the neutrino oscillation parameters is reviewed. A window to the future is finally opened by discussing projects and efforts in future detectors, beams, and analysis.

hep-ph↗

arXiv2016

Influence of short-range correlations in neutrino-nucleus scattering

Background: Nuclear short-range correlations (SRCs) are corrections to mean-field wave functions connected with the short-distance behavior of the nucleon-nucleon interaction. These SRCs provide corrections to lepton- nucleus cross sections as computed in the impulse approximation (IA). Purpose: We want to investigate the influence of SRCs on the one-nucleon (1N) and two-nucleon (2N) knockout channel for muon-neutrino induced processes on a $^{12}$C target at energies relevant for contemporary measurements. Method: The model adopted in this work, corrects the impulse approximation for SRCs by shifting the com- plexity induced by the SRCs from the wave functions to the operators. Due to the local character of the SRCs, it is argued that the expansion of these operators can be truncated at a low order. Results: The model is compared with electron-scattering data, and two-particle two-hole responses are presented for neutrino scattering. The contributions from the vector and axial-vector parts of the nuclear current as well as the central, tensor and spin-isospin part of the SRCs are studied. Conclusions: Nuclear SRCs affect the 1N knockout channel and give rise to 2N knockout. The exclusive neutrino-induced 2N knockout cross section of SRC pairs is shown and the 2N knockout contribution to the QE signal is calculated. The strength occurs as a broad background which extends into the dip region.

nucl-th↗

arXiv2016

Correlations in neutrino-nucleus scattering

We present a detailed study of charged-current quasielastic neutrino-nucleus scattering and of the influence of correlations on one- and two-nucleon knockout processes. The quasielastic neutrino-nucleus scattering cross sections, including the influence of long-range correlations, are evaluated within a continuum random phase approximation approach. The short-range correlation formalism is implemented in the impulse approximation by shifting the complexity induced by the correlations from the wave functions to the operators. The model is validated by confronting $(e,e^\prime)$ cross-section predictions with electron scattering data in the kinematic region where the quasielastic channel is expected to dominate. Further, the $^{12}$C$(ν,μ^-)$ experiments are studied. Double differential cross sections relevant for neutrino-oscillation $^{12}$C$(ν,μ^-)$ cross sections, accounting for long- and short-range correlations in the one-particle emission channel and short-range correlations in the two-particle two-hole channel, are presented for kinematics relevant for recent neutrino-nucleus scattering measurements.

nucl-th↗