1,619 research outputs found
Decay of Hypernuclei
We present a nonrelativistic transition potential for the weak
strangeness-changing reaction . The potential is based on a
one meson exchange model (OME), where, in addition to the long-ranged pion, the
exchange of the pseudoscalar , as well as the vector mesons is considered. Results obtained for different hypernuclear decay
observables are compared to the available experimental data.Comment: 8 pages. Invited talk given at the KEK-Tanashi International
Symposium on Physics of Hadrons and Nuclei. Tokyo, Japan, December 14-17,
1998. In honor of Prof. K. Yazaki. Submitted to Nucl. Phys. A. LateX file
(uses espcrc1.sty
Nonmesonic Weak Decay of Hypernuclei within a Nuclear Matter Formalism
The nonmesonic weak decay of hypernuclei using nonrelativistic
nuclear matter is studied. As the basic building block we use the Polarization
Propagator Method developed by Oset and Salcedo.
It is shown that the exact calculation of exchange terms is required. Using
the Local Density Approximation we evaluate the nonmesonic decay width for
and compare the result with a finite nucleus calculation,
obtaining a qualitative agreement.Comment: 28 pages, 3 figure
Quantum interference terms in nonmesonic weak decay of -hypernuclei within a RPA formalism
Single and double coincidence nucleon spectra in the -hypernuclei
weak decay are evaluated and discussed using a microscopic formalism. Nuclear
matter is employed together with the local density approximation which allows
us to analyze the hypernucleus non-mesonic weak decay. Final
state interactions (FSI) are included via the first order (in the nuclear
residual interaction) terms to the RPA, where the strong residual interaction
is modelled by a Bonn potential. At this level of approximation, these FSI are
pure quantum interference terms between the primary decay
and , where the strong interaction is responsible
for the last piece in the second reaction. Also the Pauli exchange
contributions are explicitly evaluated. We show that the inclusion of Pauli
exchange terms is important. A comparison with data is made. We conclude that
the limitations in phase space in the RPA makes this approximation inadequate
to reproduce the nucleon spectra. This fact, does not allow us to draw a
definite conclusion about the importance of the interference terms.Comment: 39 pages, 10 figure
The Weak Decay of Hypernuclei
The nonmesonic weak decay of hypernuclei is studied in a shell
model framework. A complete strangeness-changing weak
transition potential, based on one boson exchange, is constructed by including
the exchange of the pseudoscalar mesons , K, as well as the vector
mesons , and K, whose weak coupling constants are obtained
from soft meson theorems and SU(6). General expressions for nucleons in
arbitrary shells are obtained. The transition matrix elements include realistic
N short-range correlations and NN final state interactions based on
the Nijmegen baryon-baryon potential. The decay rates are found to be
especially sensitive to the inclusion of the strange mesons, K and K, even
though the role of kaon exchange is found to be reduced with recent couplings
obtained from next-to-leading order Chiral Perturbation Theory. With the weak
couplings used in this study the rates remain dominated by the pion-exchange
mechanism since the contributions of heavier mesons either cancel each other or
are suppressed by form factors and short-range correlations. The total decay
rate therefore remains in agreement with present measurements. However, the
partial rates which are even more sensitive to the inclusion of heavier mesons
cannot be reconciled with the data. The proton asymmetry changes by 50% once
heavier mesons are included and agrees with the available data.Comment: 70 pages, 8 figures, epsf.tex, revtex, submitted to Phys. Rev.
Microscopic approach to the proton asymmetry in the non-mesonic weak decay of Lambda-hypernuclei
The non--mesonic weak decay of polarized -hypernuclei is studied
with a microscopic diagrammatic formalism in which one- and two-nucleon induced
decay mechanisms, and , are
considered together with (and on the same ground of) nucleon final state
interactions. We adopt a nuclear matter formalism extended to finite nuclei via
the local density approximation. Our approach adopts different
one-meson-exchange weak transition potentials, while the strong interaction
effects are accounted for by a Bonn nucleon-nucleon interaction. We also
consider the two-pion-exchange effect in the weak transition potential. Both
the two-nucleon induced decay mechanism and the final state interactions reduce
the magnitude of the asymmetry. The quantum interference terms considered in
the present microscopic approach give rise to an opposite behavior of the
asymmetry with increasing energy cuts to that observed in models describing the
nucleon final state interactions semi-classically via the intranuclear cascade
code. Our results for the asymmetry parameter in C obtained
with different potential models are consistent with the asymmetry measured at
KEK
Kinematical and nonlocality effects on the nonmesonic weak hypernuclear decay
We derive in detail the transition potential for nonmesonic
lambda-hypernuclear decay in a one-meson-exchange model involving the full
pseudoscalar and vector meson octets and including two effects that have been
systematically omitted in the literature. These are the kinematical effects due
to the difference between the lambda and nucleon masses and the first-order
nonlocality corrections. Numerical results for C and
He are presented and they show that the combined kinematical plus
nonlocal corrections have an appreciable influence on the partial decay rates.
However, this is somewhat diminished in the main decay observables: the total
nonmesonic rate, the neutron-to-proton branching ratio, and the asymmetry
parameter. The latter two still cannot be reconciled with the available
experimental data. The existing theoretical predictions for the sign of the
asymmetry parameter in He are confirmed.Comment: 36 pages; LaTeX2e; 1 eps figure. Changes: 2 more tables and 14 new
references added; effects on asymmetry parameter calculated; discussions
expanded; more definite conclusions reache
La Cova del Cavall y unos enterramientos en urna de Liria
Dada la actualidad que están teniendo los estudios sobre la Primera Edad del Hierro y los orígenes de la Cultura Ibérica, hemos creído oportuno revisar el material de la Cova del Cavall y de los enterramientos del Collado de la Cova del Cavall y del Puntalet, los tres en Liria, con el fin de darles una nueva valoración a la luz de los últimos descubrimientos y estudios
De la naturaleza muerta al paisaje con figuras en la arqueología ibérica
Breve reflexión sobre la introducción de imágenes para ilustrar trabajos científicos sobre los iberos.Sin pretender la exhaustividad, se hará un repaso a la introducción de la imagen en las publicaciones sobre el mundo ibérico (catálogos y trabajos de carácter más científico). A partir de los años 90 del siglo pasado, sobre todo, se van introduciendo restituciones de espacios primero sin personas (la naturaleza muerta) para introducir tímidamente a los protagonistas (paisaje con figuras).
Puede parecer un tema anecdótico pero es el reflejo de los avances teóricos experimentados en esos años como la arqueología de género que pone en valor las personas, no sólo los objetos y los espacios. Obliga a los investigadores a reflexionar sobre no sólo sobre el uso de los objetos sino también sobre los usuarios, sobre los espacios y sus ocupantes.Short reflexion related with the introduction images in the scientific papers about the iberians
Informe Mesa de Comunicaciones 11. Docencia y Evaluación: Reflexiones y Nuevas Propuestas
El Informe tiene como objetivo presentar, unificar y sintetizar las comunicaciones presentadas en la Mesa nº 11 de las XII Jornadas de Redes de Investigación en Docencia Universitaria celebradas en el curso académico 2013-2014 en la Universidad de Alicante y que han tenido por título genérico “El reconocimiento docente: Innovar e investigar con criterios de calidad” Asimismo pretendemos recoger el debate mantenido a la finalización de la mesa entre los asistentes y ponentes
- …