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 $\Delta$-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.Comment: 8 pages, 5 figures and 1 tabl

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.Comment: 35 pages, 13 figure

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 $\Delta$ 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.Comment: 5 pages, 6 figure

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.Comment: 11 pages, 6 figures, Proccedings of the Workshop "Advanced Aspects in Nuclear Structure and Reactions at Different Energy Scales", 25-28 April 2017, Arbanasi, Bulgari

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.Comment: 9 pages, 8 figure

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 $(\nu_\mu,\mu^-)$ 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 $(\omega,q)$-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 $\Delta$ isobar current. We also analyze other effects including exchange contributions and the effect of the axial and vector currents.Comment: 9 pages and 8 figure

Neutrino-Oxygen CC0π\pi 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 $\nu_\mu$-$^{16}$O data, finding good agreement at all kinematics. We show that the results are very similar to those obtained for $\nu_\mu-^{12}$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.Comment: 28 pages, 10 figures, JLAB-THY-17-2586. Version 2 accepted for publication in Journal of Physics G: Nucl. Part. Phy

Análisis multisensor para el estudio de los patrones de turbidez en el estuario del Guadalquivir

Revista oficial de la Asociación Española de Teledetección[EN] A detailed study of the mechanisms generated through the turbidity plume and its variability at the Guadalquivir estuary has been carried out with remote sensing and in situ data. Several sensors with different characteristics have been required (spatial, temporal and spectral resolution), thereby providing information for a multi-sensor analysis. The main objective was to determine the water quality parameters (suspended solids and chlorophyll) and implement the methodology to define the empirical and semi-analytical algorithms from satellite data (MODIS, METIS, Deimos-1). The processes occurred in the estuary and adjacent region have been examined identifying those involved in the different variability scales. The forcings associated with rainfall and discharge from Alcalá del Río dam in addition to the climatic NAO index control seasonal and inter-annual fluctuations, while tide effects (semi-daily and fortnightly cycles) modulate the plume at the mouth throughout the year with significant variability. Special emphasis is focused on diagnosing the role of these mechanisms on the continental shelf ecosystems, constituting a powerful tool for the water quality management and coastal resources.[ES] En este trabajo se ha realizado un estudio detallado de los mecanismos que se desarrollan a través de la generación de la pluma de turbidez en la desembocadura del estuario del Guadalquivir, determinando su variabilidad mediante el uso conjunto de técnicas de teledetección y datos in situ. La investigación que se aborda ha requerido el uso de numerosos sensores con diferentes características (resolución espacial, temporal y espectral), proporcionando de esta manera información para realizar un análisis multisensor. El principal objetivo ha sido describir los parámetros de calidad de las aguas (sólidos en suspensión y clorofila) e implementar la metodología para generar los algoritmos empíricos y semianalíticos a partir de datos satelitales de distinta índole (MODIS, MERIS, Deimos-1). Se han exami-nado los procesos que acontecen en el estuario y región adyacente caracterizando los patrones espacio-temporales e identificando los agentes implicados en las diversas escalas de variabilidad. El forzamiento océano-meteorológico asociado a las precipitaciones, las descargas de la presa de Alcalá del Río y el índice climático NAO controlan las fluctuaciones estacionales e inter-anuales, mientras que el efecto de la marea (ciclo semi-diario y quincenal) en la desembocadura modula la pluma de turbidez a lo largo de todo el año, exhibiendo una variabilidad significativa. Se hace un especial énfasis en diagnosticar el papel que tienen dichos procesos de turbidez sobre los ecosistemas en el entorno de la plataforma continental y golfo de Cádiz, constituyendo, de tal manera, una potente herramienta para los programas de gestión integral de calidad del agua y de los recursos litorales.Este trabajo ha sido realizado gracias a la concesión de una Beca de Formación de Personal Investigador del Proyecto de Excelencia de la Junta de Andalucía titulado “Estudio de los eventos de turbidez en la desembocadura del Guadalquivir mediante teledetección y su conexión con procesos meteorológicos y oceanográficos” (P09-RNM-4853) y PIE201530I012. Nos gustaría agradecer a la ESA, NASA y Deimos-Imaging por la distribución de los datos de satélite utilizados en este estudio.Caballero, I.; Navarro, G. (2016). Multi-sensor analysis to study turbidity patterns in the Guadalquivir estuary. Revista de Teledetección. (46):1-17. https://doi.org/10.4995/raet.2016.5717SWORD1174