1,535 research outputs found
On the role of ground state correlations in hypernuclear non-mesonic weak decay
The contribution of ground state correlations (GSC) to the non--mesonic weak
decay of C and other medium to heavy hypernuclei is studied
within a nuclear matter formalism implemented in a local density approximation.
We adopt a weak transition potential including the exchange of the complete
octets of pseudoscalar and vector mesons as well as a residual strong
interaction modeled on the Bonn potential. Leading GSC contributions, at first
order in the residual strong interaction, are introduced on the same footing
for all isospin channels of one-- and two--nucleon induced decays. Together
with fermion antisymmetrization, GSC turn out to be important for an accurate
determination of the decay widths. Besides opening the two--nucleon stimulated
decay channels, for C GSC are responsible for 14% of the rate
while increasing the ratio by 4%. Our final
results for C are: ,
and . The
saturation property of with increasing hypernuclear mass
number is clearly observed. The agreement with data of our predictions for
, and is rather good.Comment: 32 pages, 9 figure
Microscopic Approach to Nucleon Spectra in Hypernuclear Non-Mesonic Weak Decay
A consistent microscopic diagrammatic approach is applied for the first time
to the calculation of the nucleon emission spectra in the non-mesonic weak
decay of Lambda-hypernuclei. We adopt a nuclear matter formalism extended to
finite nuclei via the local density approximation, a one--meson exchange weak
transition potential and a Bonn nucleon-nucleon strong potential. Ground state
correlations and final state interactions, at second order in the
nucleon--nucleon interaction, are introduced on the same footing for all the
isospin channels of one- and two-nucleon induced decays. Single and
double--coincidence nucleon spectra are predicted for 12_Lambda^C and compared
with recent KEK and FINUDA data. The key role played by quantum interference
terms allows us to improve the predictions obtained with intranuclear cascade
codes. Discrepancies with data remain for proton emission.Comment: 11 pages, 6 figures, 2 tables. To be published in Physics Letters
The Non-Mesonic Weak Decay of Double-Lambda Hypernuclei: A Microscopic Approach
The non--mesonic weak decay of double-- hypernuclei is studied
within a microscopic diagrammatic approach. Besides the nucleon--induced
mechanism, , widely studied in single-- hypernuclei,
additional hyperon--induced mechanisms, ,
and , are
accessible in double-- hypernuclei and are investigated here. As in
previous works on single-- hypernuclei, we adopt a nuclear matter
formalism extended to finite nuclei via the local density approximation and a
one--meson exchange weak transition potential (including the ground state
pseudoscalar and vector octets mesons) supplemented by correlated and
uncorrelated two--pion--exchange contributions. The weak decay rates are
evaluated for hypernuclei in the region of the experimentally accessible light
hypernuclei Be and B. Our
predictions are compared with a few previous evaluations. The rate for the
decay is dominated by --, -- and
--exchange and turns out to be about 2.5\% of the free decay
rate, , while the total rate for the and decays, dominated by
--exchange, amounts to about 0.25\% of . The
experimental measurement of these decays would be essential for the beginning
of a systematic study of the non--mesonic decay of strangeness
hypernuclei. This field of research could also shed light on the possible
existence and nature of the --dibaryon.Comment: 17 pages, 2 figure
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
On the effect of the Delta(1232) in hypernuclear non-mesonic weak decay: a microscopic approach
The non-mesonic weak decay of -hypernuclei is studied within a
microscopic diagrammatic approach which includes, for the first time, the
effect or the -baryon resonance. We adopt a nuclear matter formalism
extended to finite nuclei via the local density approximation, a one-meson
exchange weak transition potential, a Bonn nucleon-nucleon strong potential and
a strong potential based on the Landau-Migdal theory. Ground
state correlations and final state interactions (FSI), at second order in the
baryon-baryon strong interaction, are introduced on the same footing for all
the isospin channels of one- and two-nucleon induced decays. Weak decay rates
and single and double-coincidence nucleon spectra are predicted for
C and compared with recent KEK and FINUDA data. The
introduces new FSI-induced decay mechanisms which lead to an
improvement when comparing the obtained nucleon spectra with data, while it
turns out to have a negligible effect on the decay rates. Discrepancies with
experiment remain only for emission spectra involving protons, but are mostly
restricted to double-nucleon correlations in the non-back-to-back kinematics.Comment: 11 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1103.227
Exchange terms in the two--nucleon induced non--mesonic weak decay of --hypernuclei
The contribution of Pauli exchange terms to the two--nucleon induced
non--mesonic weak decay of C hypernuclei,
( or ), is studied within a nuclear matter formalism implemented in a
local density approximation. We have adopted a weak transition potential
including the exchange of the complete octets of pseudoscalar and vector mesons
as well as a residual strong interaction modeled on the Bonn potential. The
introduction of exchange terms turns out to reduce the two--nucleon induced
non--mesonic rate by 18% and, jointly with an increase in the one--nucleon
induced rate by the same magnitude, reveals to be significant for an accurate
determination of the full set of hypernuclear non--mesonic decay widths in
theoretical and experimental analyses.Comment: 14 pages, 3 figure
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