CC and NC pion production

The disappearance searching experiments nu_mu ---> nu_x use charged current quasielastic (CCQE) reaction to detect an arriving neutrino and reconstruct its energy, while the CC1 pi^+ production can mimic the CCQE signal process. In nu_mu --->nu_e appearance experiments, the NC1 pi^0 production process can lead to a fake e^- event by the impossibility for the detector of distinguish an arriving electron or a photon. Here we present a consistent model, from the point of view of the construction of the elemental amplitude, for the mentioned pion production background processes including bounding, smearing and final state interaction (FSI) effects in a single fashion. Results are comparable with more evolved approaches based on Monte Carlo simulations.Fil: Mariano, Alejandro Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; ArgentinaFil: Barbero, César Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; ArgentinaFil: López Castro, Gabriel. Instituto Politécnico Nacional. Centro de Investigación y de Estudios Avanzados. Departamento de Física; Méxic

Weak decay processes in pre-supernova core evolution within the gross theory

The beta decay and electron capture rates are of fundamental importance in the evolution of massive stars in a pre-supernova core. The beta decay process gives its contribution by emitting electrons in the plasma of the stellar core, thereby increasing pressure, which in turn increases the temperature. From the other side, the electron capture removes free electrons from the plasma of the star core contributing to the reduction of pressure and temperature. In this work we calculate the beta decay and electron capture rates in stellar conditions for 63 nuclei of relevance in the pre-supernova stage, employing Gross Theory as the nuclear model. We use the abundances calculated with the Saha equations in the hypothesis of nuclear statistical equilibrium to evaluate the time derivative of the fraction of electrons. Our results are compared with other evaluations available in the literature. They have shown to be one order less or equal than the calculated within other models. Our results indicate that these differences may influence the evolution of the star in the later stages of pre-supernova. © 2014. The American Astronomical Society. All rights reserved..Fil: Ferreira, R. C.. Universidade Estadual Do Sudoeste Da Bahía; BrasilFil: Dimarco, A. J.. Universidade Estadual de Santa Cruz, Bahía, Brasil; BrasilFil: Samana, Arturo Rodolfo. Universidade Estadual de Santa Cruz, Bahía, Brasil; BrasilFil: Barbero, César Alberto. Universidad Nacional de La Plata. Facultad de Ciencias Exactas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Single photon production νlN→νlNγ in neutrino-nucleon scattering

The quasielastic charged current (CCQE) νen→e⎯pνen→e−p scattering is the dominant mechanism to detect appearance of a νe in an almost νμ flux at the 1 GeV scale. Actual experiments show a precision below 1% and between less known background contributions, but necessary to constraint the event excess, we have the radiative corrections. A consistent model recently developed for the simultaneous description of elastic and radiative πN scattering, pion-photoproduction and single pion production processes, both for charged and neutral current neutrino-nucleon scattering, is extended for the evaluation of the radiative νlN→νlNγνlN→νlNγ cross section. Our results are similar to a previous (but inconsistent) theoretical evaluation in the low energy region, and show an increment in the upper region where the Δ resonance becomes relevant.Facultad de Ciencias Exacta

2p2h effects on the weak pion production cross section

The νln → l−p QE reaction on the A-target is used as a signal event or/and to reconstruct the neutrino energy, using two-body kinematics. Competition of another processes could lead to misidentification of the arriving neutrinos, being important the fake events coming from the CC1π background. A precise knowledge of cross sections is a prerequisite in order to make simulations in event generators to substract the fake ones from the QE countings, and in this contribution we analyze the different nuclear effects on the CC1π channel. Our calculations also can be extended for the NC case.Instituto de Física La Plat

Decaimientos beta doble exóticos

Analizamos los decaimientos beta doble exóticos sin emisión de neutrinos, con (ββM) y sin emisión de majorón (ββ0ν) que son las potenciales ventanas hacia la nueva física más allá del modelo estándar de las interacciones electrobébiles. A saber: (i) Presentamos una derivación de la probabilidad de decaimiento (ββ0ν) especialmente adaptada para los cálculos de estructura nuclear. Mostramos que la expansión de Fourier- Bessel de las corrientes hadrónicas, junto con el reacoplamiento de impulsos angulares, lleva a expresiones finales muy simples para los factores de forma nucleares. El formalismo desarrollado es aplicado a los núcleos 48Ca, 76Ge, 82Se, 100Mo, 126Te y 130Te, dentro del modelo de fases al azar para cuasipartículas. Obtenemos las expresiones analíticas explícitas en el modelo de un solo nivel para el decaimiento (ββ0ν) de 48Ca. Estas son útiles tanto para verificar los cálculos numéricos como para estudiar analíticamente la consistencia con otros formalismos. Deducimos límites sobre los términos que violan el número leptónico en el Hamiltoniano débil. (ii) Examinamos en detalle las predicciones del modelo de ”majoron cargado” introducido por Burgess y Cline. Las probabilidades de transición calculadas son mucho más pequeñas que los límites experimentales superiores sobre posibles emisiones de majorón, excepto en una pequeña región del espacio de parámetros del modelo. (iii) Estudiamos la posible competencia de los procesos exóticos con el decaimiento beta doble estándar con dos-neutrinos (ββ2ν) Discutimos la contribución de términos de orden superior en el Hamiltoniano débil. Concluimos que es muy poco probable que sus efectos dificulten la detección de los decaimientos exóticos.Tesis digitalizada en SEDICI gracias a la Biblioteca de Física de la Facultad de Ciencias Exactas (UNLP).Facultad de Ciencias Exacta

Scattering of GeV electrons in the framework of the relativistic Hartree approximation

The high momentum transfer electron-nucleus scattering cross section is evaluated within the plane wave impulse approximation (PWIA) supplemented by the relativistic Hartree approximation (RHA). Binding effects on the struck nucleon are introduced through the scalar and vector meson-exchange fields within the framework of quantum hadrodynamics. This model naturally satisfies the current conservation, with the off-shell nucleons behaving as being on the mass shell but having an effective mass. The nucleon inelastic response is included via different parameterizations of the structure function measured at SLAC, while the smearing of the Fermi surface is introduced through a momentum distribution obtained from a perturbative nuclear matter calculation. Recent CEBAF data on inclusive scattering of 4.05 GeV electrons on 56Fe are well reproduced for all measured geometries by the first time. Scaling effects are analyzed as well, and the scaling properties of the nuclear response in terms of the y variable associated to the PWIA within the RHA framework are discussed. The theoretical scaling function obtained in our approach also significantly improves previous PWIA calculations within the multi-GeV electron scattering regime, and describes properly the CEBAF scaling data.Facultad de Ciencias Exacta

Simple analytical expression for vector hypernuclear asymmetry in nonmesonic decay of 5Λ He and 12Λ C

We present general explicit expressions for a shell-model calculation of the vector hypernuclear parameter in nonmesonic weak decay. We use a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (π, η, K, ρ, ω, K*). In contrast to the approximated formula widely used in the literature, we correctly treat the contribution of transitions originated from single-proton states beyond the s-shell. Exact and simple analytical expressions are obtained for the particular cases of 5ΛHe and 12ΛC, within the one-pion-exchange model. Numerical computations of the asymmetry parameter, aΛ, are presented. Our results show a qualitative agreement with other theoretical estimates but also a contradiction with recent experimental determinations. Our simple analytical formulas provide a guide in searching the origin of such discrepancies, and they will be useful for helping to solve the hypernuclear weak decay puzzle.Facultad de Ciencias Exacta

Asymmetry parameter for the nonmesonic decay of Λ5He

We report the preliminary result of an exact calculation of the asymmetry parameter, aΛ, in the nonmesonic hypernuclear decay, based on a one-meson-exchange (OME) model. For the case of Λ 5He and including one-pion-exchange only, the result is shown not to differ considerably from the one obtained with the approximate formula widely used in the literature. In particular, the sign of aΛ remains negative, in disagreement with its most recent experimental determination. Whether these facts remain true for heavier hypernuclei and in a more complete OME model is still under investigation.Facultad de Ciencias Exacta

Decaimientos beta doble exóticos

Analizamos los decaimientos beta doble exóticos sin emisión de neutrinos, con (ββM) y sin emisión de majorón (ββ0ν) que son las potenciales ventanas hacia la nueva física más allá del modelo estándar de las interacciones electrobébiles. A saber: (i) Presentamos una derivación de la probabilidad de decaimiento (ββ0ν) especialmente adaptada para los cálculos de estructura nuclear. Mostramos que la expansión de Fourier- Bessel de las corrientes hadrónicas, junto con el reacoplamiento de impulsos angulares, lleva a expresiones finales muy simples para los factores de forma nucleares. El formalismo desarrollado es aplicado a los núcleos 48Ca, 76Ge, 82Se, 100Mo, 126Te y 130Te, dentro del modelo de fases al azar para cuasipartículas. Obtenemos las expresiones analíticas explícitas en el modelo de un solo nivel para el decaimiento (ββ0ν) de 48Ca. Estas son útiles tanto para verificar los cálculos numéricos como para estudiar analíticamente la consistencia con otros formalismos. Deducimos límites sobre los términos que violan el número leptónico en el Hamiltoniano débil. (ii) Examinamos en detalle las predicciones del modelo de ”majoron cargado” introducido por Burgess y Cline. Las probabilidades de transición calculadas son mucho más pequeñas que los límites experimentales superiores sobre posibles emisiones de majorón, excepto en una pequeña región del espacio de parámetros del modelo. (iii) Estudiamos la posible competencia de los procesos exóticos con el decaimiento beta doble estándar con dos-neutrinos (ββ2ν) Discutimos la contribución de términos de orden superior en el Hamiltoniano débil. Concluimos que es muy poco probable que sus efectos dificulten la detección de los decaimientos exóticos.Tesis digitalizada en SEDICI gracias a la Biblioteca de Física de la Facultad de Ciencias Exactas (UNLP).Facultad de Ciencias Exacta

Scattering of GeV electrons in the framework of the relativistic Hartree approximation

The high momentum transfer electron-nucleus scattering cross section is evaluated within the plane wave impulse approximation (PWIA) supplemented by the relativistic Hartree approximation (RHA). Binding effects on the struck nucleon are introduced through the scalar and vector meson-exchange fields within the framework of quantum hadrodynamics. This model naturally satisfies the current conservation, with the off-shell nucleons behaving as being on the mass shell but having an effective mass. The nucleon inelastic response is included via different parameterizations of the structure function measured at SLAC, while the smearing of the Fermi surface is introduced through a momentum distribution obtained from a perturbative nuclear matter calculation. Recent CEBAF data on inclusive scattering of 4.05 GeV electrons on 56Fe are well reproduced for all measured geometries by the first time. Scaling effects are analyzed as well, and the scaling properties of the nuclear response in terms of the y variable associated to the PWIA within the RHA framework are discussed. The theoretical scaling function obtained in our approach also significantly improves previous PWIA calculations within the multi-GeV electron scattering regime, and describes properly the CEBAF scaling data.Facultad de Ciencias Exacta