arXiv subjects

I. Ruiz Simo

Publications and source records attributed to I. Ruiz Simo.

At least 37 records · Page 2Linked to original sources

arXiv2019

Nucleon and nuclear structure functions with non-perturbative and higher order perturbative QCD effects

We have studied the nucleon structure functions $F_{iN}^{EM} (x,Q^2);~i=1,2$, by including contributions due to the higher order perturbative QCD effect up to NNLO and the non-perturbative effects due to the kinematical and dynamical higher twist (HT) effects. The numerical results for $F_{iN}^{EM}(x,Q^2)$ are obtained using Martin, Motylinski, Harland-Lang, Thorne (MMHT) 2014 NLO and NNLO nucleon parton distribution functions (PDFs). The dynamical HT correction has been included following the renormalon approach as well as the phenomenological approach and the kinematical HT effect is incorporated using the works of Schienbein et al. These nucleon structure functions have been used as an input to calculate the nuclear structure functions $F_{iA}^{EM} (x,Q^2)$. In a nucleus, the nuclear corrections arise because of the Fermi motion, binding energy, nucleon correlations, mesonic contribution, shadowing and antishadowing effects. These nuclear corrections are taken into account in the numerical calculations to obtain the nuclear structure functions $F_{iA}^{EM} (x,Q^2)$, for the various nuclear targets like $^{12}C$, $^{27}Al$, $^{56}Fe$, $^{64}Cu$, $^{118}Sn$, $^{197}Au$ and $^{208}Pb$ which are of experimental interest. The effect of isoscalarity correction for nonisoscalar nuclear targets has also been studied. The results for the $F_{iA}^{EM} (x,Q^2)$ are compared with nCTEQ nuclear PDFs parameterization as well as with the experimental results from JLab, SLAC and NMC in the kinematic region of $0.1 \le x \le 0.8$ for several nuclei.

hep-ph↗

arXiv2019

Neutrino-Oxygen CC0$π$ scattering in the SuSAv2-MEC model

We present the predictions of the SuSAv2-MEC model for the double differential charged-current muonic neutrino (antineutrino) cross section on water for the T2K neutrino (antineutrino) beam. We validate our model by comparing with the available inclusive electron scattering data on oxygen and compare our predictions with the recent T2K $ν_μ$-$^{16}$O data, finding good agreement at all kinematics. We show that the results are very similar to those obtained for $ν_μ-^{12}$C scattering, except at low energies, and we comment on the origin of this difference. A factorized spectral function model of $^{16}$O is also included for purposes of comparison.

nucl-th↗

arXiv2018

A realistic spectral function model for charged-current quasielastic-like neutrino and antineutrino cross sections on $^{12}$C

A detailed study of charged current quasielastic neutrino and antineutrino scattering cross sections on a $^{12}$C target with no pions in the final state is presented. The initial nucleus is described by means of a realistic spectral function $S(p,{\cal E})$ in which nucleon-nucleon correlations are implemented by using natural orbitals through the Jastrow method. The roles played by these correlations and by final-state interactions are analyzed and discussed. The model also includes the contribution of weak two-body currents in the two-particle two-hole sector, evaluated within a fully relativistic Fermi gas. The theoretical predictions are compared with a large set of experimental data for double-differential, single-differential and total integrated cross sections measured by the MiniBooNE, MINER$ν$A and T2K experiments. Good agreement with experimental data is found over the whole range of neutrino energies. The results are also in global good agreement with the predictions of the superscaling approach, which is based on the analysis of electron-nucleus scattering data, with only a few differences seen at specific kinematics.

nucl-th↗

arXiv2018

Quasielastic charged-current neutrino scattering in the scaling model with relativistic effective mass

We use a recent scaling analysis of the quasielastic electron scattering data from $^{12}$C to predict the quasielastic charge-changing neutrino scattering cross sections within an uncertainty band. We use a scaling function extracted from a selection of the $(e,e')$ cross section data, and an effective nucleon mass inspired by the relativistic mean-field model of nuclear matter. The corresponding super-scaling analysis with relativistic effective mass (SuSAM*) describes a large amount of the electron data lying inside a phenomenological quasielastic band. The effective mass incorporates the enhancement of the transverse current produced by the relativistic mean field. The scaling function incorporates nuclear effects beyond the impulse approximation, in particular meson-exchange currents and short range correlations producing tails in the scaling function. Besides its simplicity, this model describes the neutrino data as reasonably well as other more sophisticated nuclear models.

nucl-th↗

arXiv2018

Meson-exchange currents and quasielastic predictions for neutrino-nucleus scattering

We review some recent progress in the study of electroweak interactions in nuclei within the SuSAv2-MEC model. The model has the capability to predict (anti)neutrino scattering observables on different nuclei. The theoretical predictions are compared with the recent T2K $ν_μ-^{16}$O data and good agreement is found at all kinematics. The results are very similar to those obtained for $ν_μ-^{12}$C scattering, except at low energies, where some differences emerge. The role of meson-exchange currents in the two-particle two-hole channel is analyzed in some detail. In particular it is shown that the density dependence of these contributions is different from what is found for the quasielastic response.

nucl-th↗

arXiv2018

Low energy peripheral scaling in Nucleon-Nucleon Scattering and uncertainty quantification

We analyze the peripheral structure of the nucleon-nucleon interaction for LAB energies below 350 MeV. To this end we transform the scattering matrix into the impact parameter representation by analyzing the scaled phase shifts $(L+1/2) δ_{JLS} (p)$ and the scaled mixing parameters $(L+1/2)ε_{JLS}(p)$ in terms of the impact parameter $b=(L+1/2)/p$. According to the eikonal approximation, at large angular momentum $L$ these functions should become an universal function of $b$, {\it independent} on $L$. This allows to discuss in a rather transparent way the role of statistical and systematic uncertainties in the different long range components of the two-body potential. Implications for peripheral waves obtained in chiral perturbation theory interactions to fifth order (N5LO) or from the large body of NN data considered in the SAID partial wave analysis are also drawn from comparing them with other phenomenological high-quality interactions, constructed to fit scattering data as well. We find that both N5LO and SAID peripheral waves disagree more than $5 σ$ with the Granada-2013 statistical analysis, more than $ 2 σ$ with the 6 statistically equivalent potentials fitting the Granada-2013 database and about $1 σ$ with the historical set of 13 high-quality potentials developed since the 1993 Nijmegen analysis.

nucl-th↗

arXiv2017

Fermi-momentum dependence of relativistic effective mass below saturation from superscaling of quasielastic electron scattering

The relativistic effective mass $M^*$, and Fermi momentum, $k_F$, are important ingredients in the determination of the nuclear equation of state, but they have rarely been extracted from experimental data below saturation density where translationally invariant nuclear matter becomes unstable against clusterization into the existing atomic nuclei. Using a novel kind of superscaling analysis of the quasielastic cross section electron scattering data involving a suitable selection criterion and $^{12}$C as a reference nucleus, the global scaling properties of the resulting set of data for 21 nuclei ranging from $^2$H to $^{238}$U are then analyzed. We find that a subset of a third of the about $20000$ data approximately scales to an universal superscaling function with a more constrained uncertainty band than just the reference $^{12}$C case and provides $M^*$ as a function of $k_F$.

nucl-th↗

arXiv2017

Nuclear dependence of the 2p2h electroweak response in the Relativistic Fermi Gas model

We present the results of a recent study of meson-exchange two-body currents in lepton-nucleus inclusive scattering at various kinematics and for different nuclei within the Relativistic Fermi Gas model. We show that the associated nuclear response functions at their peaks scale as $A k_F^2$, for Fermi momentum $k_F$ going from 200 to 300 MeV/c and momentum transfer $q$ from $2k_F$ to 2 GeV/c. This behavior is different from what is found for the quasielastic response, which scales as $A/k_F$. This result can be valuable in the analyses of long-baseline neutrino oscillation experiments, which need to implement these nuclear effects in Monte Carlo simulations for different kinematics and nuclear targets.

nucl-th↗

arXiv2017

Two-nucleon emission in neutrino and electron scattering from nuclei: the modified convolution approximation

The theoretical formalism of inclusive lepton-nucleus scattering in the two-nucleon emission channel is discussed in the context of a simplified approach, the modified convolution approximation. This allows one to write the 2p2h responses of the relativistic Fermi gas as a folding integral of two 1p1h responses with the energies and momenta transferred to each nucleon. The idea behind this method is to introduce different average momenta for the two initial nucleons in the matrix elements of the two-body current, with the innovation that they depend on the transferred energies and momenta. This method treats exactly the two-body phase space kinematics, and reduces the formulae of the response functions from seven-dimensional integrals over momenta to much simpler three-dimensional ones. The applicability of the method is checked by comparing with the full results within a model of electroweak meson-exchange currents. The predictions are accurate enough, especially in the low-energy threshold region where the average momentum approximation works the best.

nucl-th↗

arXiv2017

Nuclear dependence of $R=\frac{σ_L}{σ_T}$ and Callan-Gross relation in nuclei

The electromagnetic nuclear structure functions $F_{1A} (x,Q^2)$, $F_{2A} (x,Q^2)$ and $F_{LA} (x,Q^2)$ have been calculated using a microscopic model of nucleus to study the nuclear medium effects on the ratio $R_A(x,Q^2)=\frac{σ_{LA} (x,Q^2)}{σ_{TA} (x,Q^2)} = \frac{F_{LA} (x,Q^2)}{2xF_{1A} (x,Q^2)}$ and the Callan-Gross relation(CGR) in nuclei. The nuclear medium effects due to the Fermi motion, binding energy, nucleon correlations, mesonic contribution and shadowing have been taken into account. The theoretical results for the nuclear dependence of $R_{A} (x,Q^2)$ and its impact on CGR have been presented and compared with the available experimental data on the various nuclear targets. The predictions have been made for $R_{A} (x,Q^2)$ in the kinematic region of $x$ and $Q^2$ for some nuclei relevant for the future experiments to be performed at the JLab.

hep-ph↗

arXiv2017

Coarse grained short-range correlations

We develop a scheme to take into account the effects of short-range nucleon-nucleon correlations in the nucleon-pair wave function by solving the Bethe-Goldstone equation for a coarse grained delta shell potential in S-wave configuration. The S-wave delta shell potential has been adjusted to reproduce the $^1$S$_0$ phase shifts of the AV18 potential for this partial wave up to 2 GeV in the laboratory kinetic energy. We show that a coarse grained potential can describe the high momentum tail of the back-to-back correlated pairs and the $G$-matrix in momentum space. We discuss the easiness and robustness of the calculation in coordinate space and the future improvements and utilities of this model. This work suggests the possibility of using perturbation theory for describing the short-range correlations, and related to this, to substitute the $G$-matrix by an appropriate coarse-grained potential.

nucl-th↗

arXiv2017

Density dependence of 2p-2h meson-exchange currents

We analyze the density dependence of the contribution of meson-exchange currents to the lepton-nucleus inclusive cross section in the two-particle two-hole channel. The model is based on the Relativistic Fermi Gas, where each nucleus is characterized by its Fermi momentum $k_F$. We find that the 2p-2h nuclear response functions at their peaks scale as $A k_F^2$ for Fermi momentum going from 200 to 300 MeV/c and momentum transfer $q$ from $2k_F$ to 2 GeV/c. This behavior is different from what is found for the quasielastic response, which scales as $A/k_F$. Additionally, the deep scaling region is also discussed and there the usual scaling behavior is found to be preferable.

nucl-th↗

arXiv2017

The frozen nucleon approximation in two-particle two-hole response functions

We present a fast and efficient method to compute the inclusive two-particle two-hole (2p-2h) electroweak responses in the neutrino and electron quasielastic inclusive cross sections. The method is based on two approximations. The first neglects the motion of the two initial nucleons below the Fermi momentum, which are considered to be at rest. This approximation, which is reasonable for high values of the momentum transfer, turns out also to be quite good for moderate values of the momentum transfer $q\gtrsim k_F$. The second approximation involves using in the "frozen" meson-exchange currents (MEC) an effective $Δ$-propagator averaged over the Fermi sea. Within the resulting "frozen nucleon approximation", the inclusive 2p-2h responses are accurately calculated with only a one-dimensional integral over the emission angle of one of the final nucleons, thus drastically simplifying the calculation and reducing the computational time. The latter makes this method especially well-suited for implementation in Monte Carlo neutrino event generators.

nucl-th↗

arXiv2017

Superscaling analysis of quasielastic electron scattering with relativistic effective mass

We provide a parametrization of a new phenomenological scaling function obtained from a chi-square fit to a selected set of (e,e') cross section data expanding a band centered around the quasielastic peak. We start from a re-analysis of quasielastic electron scattering from nuclear matter within the relativistic mean field model. The cross section depends on the relativistic effective mass of the nucleon, $m_N^*$, and it scales with respect to a new scaling variable, $ψ^*$. This suggests a new superscaling approach with effective mass (SuSAM*) for predicting quasielastic cross sections within an uncertainty band. The model reproduces previously established results on the enhancement of the transverse response function as compared to the traditional relativistic Fermi gas.

nucl-th↗

arXiv2016

Medium effects in the deep-inelastic charged lepton/neutrino-A scattering

In this work, we have discussed the recent developments that have taken place to understand the differences in the weak $F_{2A}^{Weak} (x,Q^2)$ and electromagnetic $F_{2A}^{EM} (x,Q^2)$ nuclear structure functions. Also we present the results of our work on nuclear medium effects on $F_{2A}^{Weak} (x,Q^2)$ and $F_{2A}^{EM} (x,Q^2)$ for a wide range of $x$ and $Q^2$. These results have been obtained using a microscopic nuclear model, where to incorporate nuclear medium effects, Fermi motion, binding energy, nucleon correlations, mesonic contributions from pion and rho mesons and shadowing effects are considered. The calculations are performed in local density approximation using relativistic nucleon spectral function. We have also compared the theoretical results with the recent experimental data on electromagnetic and weak structure functions. Furthermore, we have studied the nuclear medium effects in Drell-Yan(DY) process and present the results for differential cross section, and the results are compared with the data of E772 experiment.

nucl-th↗

arXiv2016

The role of meson exchange currents in charged current (anti)neutrino-nucleus scattering

We present our recent progress in the description of neutrino-nucleus interaction in the GeV region, of interest for ongoing and future oscillation experiments. In particular, we discuss the weak excitation of two-particle-two-hole states induced by meson exchange currents in a fully relativistic framework. We compare the results of our model with recent measurements of neutrino scattering cross sections, showing the crucial role played by two-nucleon knockout in the interpretation of the data.

nucl-th↗

arXiv2016

Charged-current neutrino-nucleus reactions within the SuSAv2-MEC approach

We present a detailed study of charged-current (CC) neutrino-nucleus reactions in a fully relativis- tic framework and comparisons with recent experiments spanning an energy range from hundreds of MeV up to 100 GeV within the SuperScaling Approach, which is based on the analysis of electron- nucleus scattering data and has been recently improved with the inclusion of Relativistic Mean Field theory effects. We also evaluate and discuss the impact of two-particle two-hole meson-exchange currents (2p-2h MEC) on neutrino-nucleus interactions through the analysis of two-particle two-hole axial and vector contributions to weak response functions in a fully relativistic Fermi gas. The results show a fairly good agreement with experimental data over the whole range of neutrino energies.

nucl-th↗

arXiv2016

Emission of neutron-proton and proton-proton pairs in neutrino scattering

We use a recently developed model of relativistic meson-exchange currents to compute the neutron-proton and proton-proton yields in $(ν_μ,μ^-)$ scattering from $^{12}$C in the 2p-2h channel. We compute the response functions and cross sections with the relativistic Fermi gas model for different kinematics from intermediate to high momentum transfers. We find a large contribution of neutron-proton configurations in the initial state, as compared to proton-proton pairs. In the case of charge-changing neutrino scattering the 2p-2h cross section of proton-proton emission ({\it i.e.,} np in the initial state) is much larger than for neutron-proton emission ({\it i.e.,} two neutrons in the initial state) by a $(ω,q)$-dependent factor. The different emission probabilities of distinct species of nucleon pairs are produced in our model only by meson-exchange currents, mainly by the $Δ$ isobar current. We also analyze other effects including exchange contributions and the effect of the axial and vector currents.

nucl-th↗