arXiv subjects

I. Ruiz Simo

Publications and source records attributed to I. Ruiz Simo.

At least 55 records · Page 3Linked to original sources

arXiv2016

Emission of neutron-proton and proton-proton pairs in electron scattering induced by meson-exchange currents

We use a relativistic model of meson-exchange currents to compute the proton-neutron and proton-proton yields in $(e,e')$ scattering from $^{12}$C in the 2p-2h channel. We compute the response functions and cross section with the relativistic Fermi gas model for a range of 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. 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 the effect of the exchange contribution and show that the direct/exchange interference strongly affects the determination of the np/pp ratio.

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arXiv2016

Nuclear medium effects in $F_{2A}^{EM}(x,Q^2)$ and $F_{2A}^{Weak}(x,Q^2)$ structure functions

Recent phenomenological analysis of experimental data on DIS processes induced by charged leptons and neutrinos/antineutrinos beams on nuclear targets by CTEQ collaboration has confirmed the observation of CCFR and NuTeV collaborations, that weak structure function $F_{2A}^{Weak} (x,Q^2)$ is different from electromagnetic structure function $F_{2A}^{EM} (x,Q^2)$ in a nucleus like iron, specially in the region of low $x$ and $Q^2$. In view of this observation we have made a study of nuclear medium effects on $F_{2A}^{Weak} (x,Q^2)$ and $F_{2A}^{EM} (x,Q^2)$ for a wide range of $x$ and $Q^2$ using a microscopic nuclear model. We have considered Fermi motion, binding energy, nucleon correlations, mesonic contributions from pion and rho mesons and shadowing effects to incorporate nuclear medium effects. The calculations are performed in a local density approximation using a relativistic nucleon spectral function which includes nucleon correlations. The numerical results in the case of iron nucleus are compared with the experimental data.

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arXiv2016

Nuclear medium effects in Drell-Yan process

We study the nuclear medium effects in Drell-Yan process using quark parton distribution functions calculated in a microscopic nuclear model which takes into account the effects of Fermi motion, nuclear binding and nucleon correlations through a relativistic nucleon spectral function. The contributions of $π$ and $ρ$ mesons as well as shadowing effects are also included. The beam energy loss is calculated using a phenomenological approach. The present theoretical results are compared with the experimental results of E772 and E886 experiments. These results are applicable to the forthcoming experimental analysis of E906 Sea Quest experiment at Fermi Lab.

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arXiv2016

Relativistic model of 2p-2h meson exchange currents in (anti)neutrino scattering

We develop a model of relativistic, charged meson-exchange currents (MEC) for neutrino-nucleus interactions. The two-body current is the sum of seagull, pion-in-flight, pion-pole and $Δ$-pole operators. These operators are obtained from the weak pion-production amplitudes for the nucleon derived in the non-linear $σ$-model together with weak excitation of the $Δ(1232)$ resonance and its subsequent decay into $Nπ$. With these currents we compute the five 2p-2h response functions contributing to $(ν_l,l^-)$ and $(\overlineν_l,l^+)$ reactions in the relativistic Fermi gas model. The total current is the sum of vector and axial two-body currents. The vector current is related to the electromagnetic MEC operator that contributes to electron scattering. This allows one to check our model by comparison with the results of De Pace {\em et al.,} Nuclear Physics A 726 (2003) 303. Thus our model is a natural extension of that model to the weak sector with the addition of the axial MEC operator. The dependences of the response functions on several ingredients of the approach are analyzed. Specifically we discuss relativistic effects, quantify the size of the direct-exchange interferences, and the relative importance of the axial versus vector current.

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arXiv2016

Electromagnetic and Weak Nuclear Structure Functions $F_{1,2}(x,Q^2)$ in the Intermediate Region of $Q^2$

We have studied nuclear structure functions $F_{1A}(x,Q^2)$ and $F_{2A}(x,Q^2)$ for electromagnetic and weak processes in the region of $1 GeV^2 < Q^2 <8 GeV^2$. The nuclear medium effects arising due to Fermi motion, binding energy, nucleon correlations, mesonic contributions and shadowing effects are taken into account using a many body field theoretical approach. The calculations are performed in a local density approximation using a relativistic nucleon spectral function. The results are compared with the available experimental data. Implications of nuclear medium effects on the validity of Callan-Gross relation are also discussed.

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arXiv2016

Effects of Nuclear Medium on the Sum Rules in Electron and Neutrino Scattering

In this work, we study the influence of nuclear medium effects on various parton model sum rules in nuclei and compare the results with the free nucleon case. We have used relativistic nucleon spectral function to take into account Fermi motion, binding and nucleon correlations. The pion and rho meson cloud contributions have been incorporated in a microscopic model. The effect of shadowing has also been considered.

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arXiv2015

Scaling violation and relativistic effective mass from quasielastic electron scattering: implications for neutrino reactions

The experimental data from quasielastic electron scattering from $^{12}$C are reanalyzed in terms of a new scaling variable suggested by the interacting relativistic Fermi gas with scalar and vector interactions, which is known to generate a relativistic effective mass for the interacting nucleons. By choosing a mean value of this relativistic effective mass $m_N^* =0.8 m_N$, we observe that most of the data fall inside a region around the inverse parabola-shaped universal scaling function of the relativistic Fermi gas. This suggests a method to select the subset of data that highlight the quasielastic region, about two thirds of the total 2,500 data. Regardless of the momentum and energy transfer, this method automatically excludes the data that are not dominated by the quasielastic process. The resulting band of data reflects deviations from the perfect universality, and can be used to characterize experimentally the quasielastic peak, despite the manifest scaling violation. Moreover we show that the spread of the data around the scaling function can be interpreted as genuine fluctuations of the effective mass $M^* \equiv m^*_N/m_N \sim 0.8 \pm 0.1$. Applying the same procedure we transport the scaling quasielastic band into a theoretical prediction band for neutrino scattering cross section that is compatible with the recent measurements and slightly more accurate.

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arXiv2015

Parity violating asymmetry with nuclear medium effects in deep inelastic $\vec e$ scattering

Recently at JLab using polarised electron beam on unpolarised deuteron target measurements have been performed for the parity violating asymmetry($A_{PV}$) and there are future plans to measure this asymmetry using various nuclear targets. In this paper, we study $A_{PV}$ in nuclear targets like $^{12}C$, $^{56}Fe$ and $^{208}Pb$, in a local density approximation using spectral function which takes into account Fermi motion, binding energy correction and nucleon correlations. Furthermore, the pion and rho cloud contributions have also been taken into account. The present model has been used earlier to study medium effects in electromagnetic as well as weak interaction induced processes in the DIS region.

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arXiv2015

Nuclear medium effects in structure functions of nucleon at moderate $Q^2$

Recent experiments performed on inclusive electron scattering from nuclear targets have measured the nucleon electromagnetic structure functions $F_1(x,Q^2)$, $F_2(x,Q^2)$ and $F_L(x,Q^2)$ in $^{12}C$, $^{27}Al$, $^{56}Fe$ and $^{64}Cu$ nuclei. The measurements have been done in the energy region of $1 GeV^2 < W^2 < 4 GeV^2$ and $Q^2$ region of $0.5 GeV^2 < Q^2 < 4.5 GeV^2$. We have calculated nuclear medium effects in these structure functions arising due to the Fermi motion, binding energy, nucleon correlations, mesonic contributions from pion and rho mesons and shadowing effects. The calculations are performed in a local density approximation using relativistic nucleon spectral function which include nucleon correlations. The numerical results are compared with the recent experimental data from JLab and also with some earlier experiments.

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arXiv2015

Weak Production of Strange Particles and $η$ Mesons off the Nucleon

The strange particle production induced by (anti)neutrino off nucleon has been studied for $|ΔS|=0$ and $|ΔS|=1$ channels. The reactions those we have considered are for the production of single kaon/antikaon, eta and associated particle production processes. We have developed a microscopical model based on the SU(3) chiral Lagrangian. The basic parameters of the model are $f_π$, the pion decay constant, Cabibbo angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet. For antikaon production we have also included $Σ^*$(1385) resonance and for eta production $S_{11}$(1535) and $S_{11}$(1650) resonances are included.

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arXiv2015

2p-2h excitations in neutrino scattering: angular distribution and frozen approximation

We study the phase-space dependence of 2p-2h excitations in neutrino scattering using the relativistic Fermi gas model. We follow a similar approach to other authors, but focusing in the phase-space properties, comparing with the non-relativistic model. A careful mathematical analysis of the angular distribution function for the outgoing nucleons is performed. Our goals are to optimize the CPU time of the 7D integral to compute the hadron tensor in neutrino scattering, and to conciliate the different relativistic and non relativistic models by describing general properties independently of the two-body current. For some emission angles the angular distribution becomes infinite in the Lab system, and we derive a method to integrate analytically around the divergence. Our results show that the frozen approximation, obtained by neglecting the momenta of the two initial nucleons inside the integral of the hadron tensor, reproduces fairly the exact response functions for constant current matrix elements.

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arXiv2014

Neutrino-nucleus CCQE-like scattering

RPA correlations, spectral function and 2p2h (multi-nucleon) effects on charged-current neutrino-nucleus reactions without emitted pions are discussed. We pay attention to the influence of RPA and multi-nucleon mechanisms on the MiniBooNE and MINERvA flux folded differential cross sections, the MiniBooNE flux unfolded total cross section and the neutrino energy reconstruction.

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arXiv2014

Testing nuclear models via neutrino scattering

Recent progresses on the relativistic modeling of neutrino-nucleus reactions are presented and the results are compared with high precision experimental data in a wide energy range.

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arXiv2014

Angular distribution in two-particle emission induced by neutrinos and electrons

The angular distribution of the phase space arising in two-particle emission reactions induced by electrons and neutrinos is computed in the laboratory (Lab) system by boosting the isotropic distribution in the center of mass (CM) system used in Monte Carlo generators. The Lab distribution has a singularity for some angular values, coming from the Jacobian of the angular transformation between CM and Lab systems. We recover the formula we obtained in a previous calculation for the Lab angular distribution. This is in accordance with the Monte Carlo method used to generate two-particle events for neutrino scattering\cite{Sob12}. Inversely, by performing the transformation to the CM system, it can be shown that the phase-space function, which is proportional to the two particle-two hole (2p-2h) hadronic tensor for a constant current operator, can be computed analytically in the frozen nucleon approximation, if Pauli blocking is absent. The results in the CM frame confirm our previous work done using an alternative approach in the Lab frame. The possibilities of using this method to compute the hadronic tensor by a boost to the CM system are analyzed.

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arXiv2014

Relativistic effects in two-particle emission for electron and neutrino reactions

Two-particle two-hole contributions to electroweak response functions are computed in a fully relativistic Fermi gas, assuming that the electroweak current matrix elements are independent of the kinematics. We analyze the genuine kinematical and relativistic effects before including a realistic meson-exchange current (MEC) operator. This allows one to study the mathematical properties of the non-trivial seven-dimensional integrals appearing in the calculation and to design an optimal numerical procedure to reduce the computation time. This is required for practical applications to CC neutrino scattering experiments, where an additional integral over the neutrino flux is performed. Finally we examine the viability of this model to compute the electroweak 2p-2h response functions.

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arXiv2014

Nuclear medium effects in Drell-Yan process

We study nuclear medium effects in Drell-Yan processes at small target x using quark parton distribution functions and nucleon structure functions for a bound nucleon calculated in a microscopic nuclear model which takes into account the effect of Fermi motion, nuclear binding and nucleon correlations through a relativistic spectral function. The contributions of $π$ and $ρ$ mesons, target mass corrections and nuclear shadowing are also included. The results are compared with the theoretical and experimental results. The model is able to successfully explain the low target x results of E772 and E866 Drell-Yan experiments and is applicable to the forthcoming experimental analysis of E906 Sea Quest experiment at Fermi Lab.

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arXiv2013

Weak Strangeness and Eta Production

We have studied strange particle production off nucleons through $ΔS =0 $ and $|ΔS| = 1$ channels, and specifically single kaon/antikaon, eta, associated particle production for neutrino/antineutrino induced processes as well as antineutrino induced single hyperon production processes. We have developed a microscopical model based on the SU(3) chiral Lagrangians. The basic parameters of the model are $f_π$, the pion decay constant, Cabibbo angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet. For antikaon production we have also included $Σ^*(1385)$ resonance and for eta production $S_{11}(1535)$ and $S_{11}(1650)$ resonances are included.

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arXiv2013

CCQE, 2p2h excitations and ν-energy reconstruction

We analyze the MiniBooNE muon neutrino CCQE-like dσ/dT_μ/dcosθ_μdata using a theoretical model that, among other nuclear effects, includes RPA correlations and 2p2h (multinucleon) mechanisms. These corrections turn out to be essential for the description of the data. We find that MiniBooNE CCQE-like data are fully compatible with former determinations of the nucleon axial mass M_A ~ 1.05 GeV. This is in sharp contrast with several previous analysis where anomalously large values of M_A ~ 1.4 GeV have been suggested. We also show that because of the the multinucleon mechanism effects, the algorithm used to reconstruct the neutrino energy is not adequate when dealing with quasielastic-like events. Finally, we analyze the MiniBooNE unfolded cross section, and show that it exhibits an excess (deficit) of low (high) energy neutrinos, which is an artifact of the unfolding process that ignores 2p2h mechanisms.

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