118 research outputs found
Sigma Exchange in the Nonmesonic Decays of Light Hypernuclei and Violation of the Delta I=1/2 Rule
Nonmesonic weak decays of s-shell hypernuclei are analyzed in microscopic
models for the Lambda N to NN weak interaction. A scalar-isoscalar meson,
sigma, is introduced and its importance in accounting the decay rates, n/p
ratios and proton asymmetry is demonstrated. Possible violation of the Delta
I=1/2 rule in the nonmesonic weak decay of Lambda is discussed in a
phenomenological analysis and several useful constraints are presented. The
microscopic calculation shows that the current experimental data indicate a
large violation of the Delta I=1/2 rule, although no definite conclusion can be
derived due to large ambiguity of the decay rate of {^4_Lambda H}.Comment: 13 pages, 5 figure
Neutron and proton spectra from the decay of hypernuclei
We have determined the spectra of neutrons and protons following the decay of
hypernuclei through the one- and two-nucleon induced mechanisms. The
momentum distributions of the primary nucleons are calculated and a Monte Carlo
simulation is used to account for final state interactions. From the spectra we
calculate the number of neutrons () and protons () per
decay and show how the measurement of these quantities, particularly , can
lead to a determination of , the ratio of neutron to
proton induced decay. We also show that the consideration of the
two-nucleon induced channel has a repercussion in the results, widening the
band of allowed values of with respect to what is
obtained neglecting this channel.Comment: 30 pages, 12 Postscript figures, uuencoded file, ReVTeX, epsf.st
Hyperonic mixing in five-baryon double-strangeness hypernuclei in a two-channel treatment
Properties of hypernuclei H and He are studied in a two-channel approach with explicit treatment of
coupling of channels ^3\text{Z}+\Lambda+\Lambda and \alpha+\Xi. Diagonal
\Lambda\Lambda and coupling \Lambda\Lambda-\Xi N interactions are derived
within G-matrix procedure from Nijmegen meson-exchange models. Bond energy
\Delta B_{\Lambda\Lambda} in He exceeds significantly
that in H due to the channel coupling. Diagonal \Xi\alpha
attraction amplifies the effect, which is sensitive also to \Lambda-core
interaction. The difference of the \Delta B_{\Lambda\Lambda} values can be an
unambiguous signature of the \Lambda\Lambda-\Xi N coupling in \Lambda\Lambda
hypernuclei. However, improved knowledge of the hyperon-nucleus potentials is
needed for quantitative extraction of the coupling strength from future data on
the \Lambda\Lambda hypernuclear binding energies.Comment: 11 pages with 3 figures; Phys. Rev. C, accepte
Final State Interactions in Hypernuclear Decay
We present an update of the One-Meson-Exchange (OME) results for the weak
decay of s- and p-shell hypernuclei (Ref. Phys. Rev. C {\bf 56}, 339 (1997)),
paying special attention to the role played by final state interactions between
the emitted nucleons. The present study also corrects for a mistake in the
inclusion of the and exchange mechanisms, which substantially
increases the ratio of neutron-induced to proton-induced transitions,
. With the most up-to-date model ingredients, we find that
the OME approach is able to describe very satisfactorily most of the measured
observables, including the ratio .Comment: 20 pages, 2 eps figure
Proton asymmetry in non-mesonic weak decay of light hypernuclei
We have obtained the decay asymmetry parameters in non-mesonic weak decay of
polarized Lambda-hypernuclei by measuring the proton asymmetry. The polarized
Lambda-hypernuclei, 5_Lambda-He, 12_Lambda-C, and 11_Lambda-B, were produced in
high statistics via the (pi^+,k^+) reaction at 1.05 GeV/c in the forward
angles. Preliminary analysis shows that the decay asymmetry parameters are very
small for these s-shell and p-shell hypernuclei.Comment: 4pages, 4figures, International Conference on Hypernuclear and
Strange Particle Physics (HYP2003
Delayed clusters accompanying nonmesonic weak decay of the -hypernuclei: a clue to nonleptonic processes
The nonmesonic decay of -hypernuclei provides access to the
nonleptonic weak decay process , which is achievable only
through the observation of hypernuclear ground-state decays. We continue the
discussion of some specific cases which make it possible to detect a few
exclusive transitions, namely, the stripping of nucleon from the ground state
results in a resonance state decaying via emission of two clusters. Delayed
clusters accompanying weak decay of light hypernuclei give a unique information
on spin dependence of the weak decay matrix elements.Comment: Presented at International Bogolyubov Conference "Problems of
Theoretical and Mathematical Physics" (dedicated to the 100th anniversary of
the birth of N.N.~Bogolyubov) Dubna, Russia, August 21 - 27, 200
Three-body decay of the d* dibaryon
Under certain circumstances, a three-body decay width can be approximated by
an integral involving a product of two off-shell two-body decay widths. This
``angle-average'' approximation is used to calculate the decay width
of the dibaryon in a simple model for the most
important Feynman diagrams describing pion emissions with baryon-baryon recoil
and meson retardation. The decay width is found to be about 0.006 (0.07, 0.5)
MeV at the mass of 2065 (2100, 2150) MeV for input dynamics derived from
the Full Bonn potential. The smallness of this width is qualitatively
understood as the result of the three-body decay being ``third forbidden''. The
concept of forbiddenness and the threshold behavior of a three-body
decay are further studied in connection with the decay of the dibaryon
where the idea of unfavorness has to be introduced.
The implications of these results are briefly discussed.Comment: 15 pages, RevTeX, two-column journal style, six figure
What Does Free Space Lambda-Lambda Interaction Predict for Lambda-Lambda Hypernuclei?
Data on Lambda-Lambda hypernuclei provide a unique method to learn details on
the strangeness S =-2 sector of the baryon-baryon interaction. From the free
space Bonn-Julich potentials, determined from data on baryon-baryon scattering
in the S=0,-1 channels, we construct an interaction in the S =-2 sector to
describe the experimentally known Lambda-Lambda hypernuclei. After including
short--range (Jastrow) and RPA correlations, we find masses for these
Lambda-Lambda hypernuclei in a reasonable agreement with data, taking into
account theoretical and experimental uncertainties. Thus, we provide a natural
extension, at low energies, of the Bonn-Julich OBE potentials to the S =-2
channel.Comment: 4 pages, 2 figures, revtex4 style. Minor changes in conclusions.
References updated. Accepted in Phys. Rev. Let
Strangeness nuclear physics: a critical review on selected topics
Selected topics in strangeness nuclear physics are critically reviewed. This
includes production, structure and weak decay of --Hypernuclei, the
nuclear interaction and the possible existence of bound
states in nuclei. Perspectives for future studies on these issues are also
outlined.Comment: 63 pages, 51 figures, accepted for publication on European Physical
Journal
Novel Weak Decays in Doubly Strange Systems
The strangeness-changing () weak baryon-baryon interaction is
studied through the nonmesonic weak decay of double- hypernuclei.
Besides the usual nucleon-induced decay we discuss novel
hyperon-induced decay modes and . These reactions provide unique access to the exotic
K and K vertices which place new constraints
on Chiral Pertubation Theory (PT) in the weak SU(3) sector. Within a
meson-exchange framework, we use the pseudoscalar octet for the
long-range part while parametrizing the short-range part through the vector
mesons . Realistic baryon-baryon forces for the and
-2 sectors account for the strong interaction in the initial and final states.
For He the new hyperon-induced decay modes account for up
to 4% of the total nonmesonic decay rate. Predictions are made for all possible
nonmesonic decay modes.Comment: 19 pages, 2 ps figures, 9 table
- …