555 research outputs found
The Lambda-Lambda Interaction and ^{6}_{Lambda Lambda}He
An OBE potential model for the ^{1}S_0 S = -2 interaction is analyzed with
emphasis on the role of coupling between the Lambda Lambda, N Xi, and Sigma
Sigma channels. Singlet scalar exchange, an approximation to two-pion exchange,
is significant in all channels; surprisingly, the one-pion exchange component
is almost negligible. The size of the channel coupling as a function of the
overall strength of the OBE model potential is examined. Implications of the
analysis for the binding energy of ^{6}_{Lambda Lambda}He are considered; the
new experimental datum may suggest a consistency between the extracted Lambda
Lambda matrix element and the relation implied by SU(3) among OBE baryon-baryon
interactions. \\Comment: 4 pages brief report to Physical Review
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
Neutron Star Constraints on the H Dibaryon
We study the influence of a possible H dibaryon condensate on the equation of
state and the overall properties of neutron stars whose population otherwise
contains nucleons and hyperons. In particular, we are interested in the
question of whether neutron stars and their masses can be used to say anything
about the existence and properties of the H dibaryon. We find that the equation
of state is softened by the appearance of a dibaryon condensate and can result
in a mass plateau for neutron stars. If the limiting neutron star mass is about
that of the Hulse-Taylor pulsar a condensate of H dibaryons of vacuum mass 2.2
GeV and a moderately attractive potential in the medium could not be ruled out.
On the other hand, if the medium potential were even moderately repulsive, the
H, would not likely exist in neutron stars. If neutron stars of about 1.6 solar
mass were known to exist, attractive medium effects for the H could be ruled
out. Certain ranges of dibaryon mass and potential can be excluded by the mass
of the Hulse-Taylor pulsar which we illustrate graphically.Comment: Revised by the addition of a figure showing the region of dibaryon
mass and potential excluded by the Hulse-Taylor pulsar. 18 pages, 11 figures,
latex (submitted to Phys. Rev. C
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
Presente y futuro de la criosfera polar, incluyendo la variabilidad del ciclo hidrológico ártico
Hyperon-hyperon interactions and properties of neutron matter
We present results from Brueckner-Hartree-Fock calculatons for beta stable
neutron star matter with nucleonic and hyperonic degress degrees of freedom,
employing the most recent parametrizations of the baryon-baryon interaction of
the Nijmegen group. It is found that the only strange baryons emergin in beta
stable matter up to total barionic densities of 1.2 fm^-3 are and
. The corresponding equations of state are then used to compute
properties of neutron stars such as masses and radii.Comment: 27 pages, LateX, includes 8 PostScript figures, (submitted to PRC
Detectability of Strange Matter in Heavy Ion Experiments
We discuss the properties of two distinct forms of hypothetical strange
matter, small lumps of strange quark matter (strangelets) and of hyperon matter
(metastable exotic multihypernuclear objects: MEMOs), with special emphasis on
their relevance for present and future heavy ion experiments. The masses of
small strangelets up to A = 40 are calculated using the MIT bag model with
shell mode filling for various bag parameters. The strangelets are checked for
possible strong and weak hadronic decays, also taking into account multiple
hadron decays. It is found that strangelets which are stable against strong
decay are most likely highly negative charged, contrary to previous findings.
Strangelets can be stable against weak hadronic decay but their masses and
charges are still rather high. This has serious impact on the present high
sensitivity searches in heavy ion experiments at the AGS and CERN facilities.
On the other hand, highly charged MEMOs are predicted on the basis of an
extended relativistic mean-field model. Those objects could be detected in
future experiments searching for short-lived, rare composites. It is
demonstrated that future experiments can be sensitive to a much wider variety
of strangelets.Comment: 26 pages, 5 figures, uses RevTeX and epsf.st
Dihyperon in Chiral Colour Dielectric Model
The mass of dihyperon with spin, parity and isospin
is calculated in the framework of Chiral colour dielectric model. The wave
function of the dihyperon is expressed as a product of two colour-singlet
baryon clusters. Thus the quark wave functions within the cluster are
antisymmetric. Appropriate operators are then used to antisymmetrize
inter-cluster quark wave functions. The radial part of the quark wavefunctions
are obtained by solving the the quark and dielectric field equations of motion
obtained in the Colour dielectric model. The mass of the dihyperon is computed
by including the colour magnetic energy as well as the energy due to meson
interaction. The recoil correction to the dihyperon mass is incorporated by
Peierls-Yoccoz technique. We find that the mass of the dihyperon is smaller
than the threshold by over 100 MeV. The implications of our
results on the present day relativistic heavy ion experiments is discussed.Comment: LaTeX, 13 page
The H-Dibaryon and the Hard Core
The H dibaryon, a single, triply magic bag containing two up, two down and
two strange quarks, has long been sought after in a variety of experiments. Its
creation has been attempted in , proton and most recently in relativistic
heavy ion induced reactions. We concentrate on the latter, but our conclusions
are more generally applicable. The two baryons coalescing to form the single
dibaryon, likely in the case of heavy ions, must penetrate
the short range repulsive barrier which is expected to exist between them. We
find that this barrier can profoundly affect the probability of producing the H
state, should it actually exist.Comment: 9 pages including 4 figure
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