6,039 research outputs found
Weak Magnetism in Two Neutrino Double Beta Decay
We have extended the formalism for the two-neutrino double beta decay by
including the weak-magnetism term, as well as other second-forbidden
corrections. The weak magnetism diminishes the calculated half-lives in , independently of the nuclear structure. Numerical computations were
performed within the pn-QRPA, for , , ,
and nuclei. No one of the second-forbidden corrections modifies
significantly the spectrum shapes. The total reduction in the calculated half
lives varies from 6% up to 32%, and strongly depend on the nuclear interaction
in the particle-particle channel. We conclude that the higher order
effects in the weak Hamiltonian would hardly be observed in the two-neutrino
double beta experiments.Comment: 8 pages, latex, 1ps figure, to appear in Phys. Lett.
Competition between standard and exotic double beta decays
We discuss the contributions of higher order terms in weak Hamiltonian to the
standard two-neutrino double beta decay. The formalism for the unique first
forbidden transitions has been developed, and it is shown that they can alter
the two-electron energy spectrum. Yet, their effect is too small to screen the
detection of exotic neutrinoless double beta decays, which are candidates for
testing the physics beyond the standard model.Comment: 9 pages, latex, 1ps figures, minor changes, to appear in Phys. Lett.
meson exchange effect on nonmesonic hypernuclear weak decay observables
We analyze the influence of meson exchange on the main nonmesonic
hypernuclear weak decay observables: the total rate, , the
neutron-to-proton branching ratio, , and the proton asymmetry
parameter, . The meson exchange is added to the standard
strangeness-changing weak transition potential, which
includes the exchange of the complete pseudoscalar and vector mesons octet
(, , , , , ). Using a shell model formalism,
the meson weak coupling constants are adjusted to reproduce the recent
and experimental data for .
Numerical results for the remaining observables of and all the
observables of decays are presented. They clearly show that
the addition of the meson, in spite of improving some observables
values, is not enough to reproduce simultaneously all the measurements, and the
puzzle posed by the experimental data remains unexplained.Comment: 4 pages, 1 figure. Submitted for publication in Phys. Re
One pion production in neutrino-nucleon scattering and the different parametrizations of the weak vertex
The weak vertex provides an important contribution to the one
pion production in neutrino-nucleon and neutrino-nucleus scattering for
invariant masses below 1.4 GeV. Beyond its interest as a tool in neutrino
detection and their background analyses, one pion production in
neutrino-nucleon scattering is useful to test predictions based on the quark
model and other internal symmetries of strong interactions. Here we try to
establish a connection between two commonly used parametrizations of the weak
vertex and form factors (FF) and we study their effects on the
determination of the axial coupling , the common normalization of the
axial FF, which is predicted to hold 1.2 by using the PCAC hypothesis.
Predictions for the total cross sections within
the two approaches, which include the resonant and other
background contributions in a coherent way, are compared to experimental data.Comment: Submitted to Physics Letters
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