328 research outputs found
Narrow Pentaquark States in a Quark Model with Antisymmetrized Molecular Dynamics
The exotic baryon is studied with microscopic
calculations in a quark model by using a method of antisymmetrized molecular
dynamics(AMD). We predict narrow states, ,
, and , which nearly degenerate in a
low-energy region of the system. We discuss decay widths and
estimate them to be for the , and
MeV for the state.Comment: Talk given at International Workshop on PENTAQUARK04, Spring-8,
Hyogo, Japan, 20-23 Jul 200
Antisymmetrized molecular dynamics studies for exotic clustering phenomena in neutron-rich nuclei
We present a review of recent works on clustering phenomena in unstable
nuclei studied by antisymmetrized molecular dynamics (AMD). The AMD studies in
these decades have uncovered novel types of clustering phenomena brought about
by the excess neutrons. Among them, this review focuses on the molecule-like
structure of unstable nuclei. One of the earliest discussions on the clustering
in unstable nuclei was made for neutron-rich Be and B isotopes. AMD
calculations predicted that the ground state clustering is enhanced or reduced
depending on the number of excess neutrons. Today, the experiments are
confirming this prediction as the change of the proton radii. Behind this
enhancement and reduction of the clustering, there are underlying shell effects
called molecular- and atomic-orbits. These orbits form covalent and ionic
bonding of the clusters analogous to the atomic molecules. It was found that
this "molecular-orbit picture" reasonably explains the low-lying spectra of Be
isotopes. The molecular-orbit picture is extended to other systems having
parity asymmetric cluster cores and to the three cluster systems. O and Ne
isotopes are the candidates of the former, while the linear chains in
C isotopes are the latter. For both subjects, many intensive studies are now in
progress. We also pay a special attention to the observables which are the
fingerprint of the clustering. In particular, we focus on the monopole and
dipole transitions which are recently regarded as good probe for the
clustering. We discuss how they have and will reveal the exotic clustering.Comment: 96 pages, 44 figure
Structure of Excited States of 10Be studied with Antisymmetrized Molecular Dynamics
We study structure of excited states of 10Be with the method of variation
after spin parity projection in the framework of antisymmetrized molecular
dynamics. Present calculations describe many excited states and reproduce the
experimental data of E2 and E1 transitions and the new data of the
transition strength successfully. We make systematic discussions on the
molecule-like structures of light unstable nuclei and the important role of the
valence neutrons based on the results obtained with the framework which is free
from such model assumptions as the existence of inert cores and clusters.Comment: 15 pages, RevTex, seven postscript figures (using epsf.sty
Superdeformation and clustering in Ca studied with Antisymmetrized Molecular Dynamics
Deformed states in Ca are investigated with a method of
antisymmetrized molecular dynamics. Above the spherical ground state,
rotational bands arise from a normal deformation and a superdeformation as well
as an oblate deformation. The calculated energy spectra and transition
strengths in the superdeformed band reasonably agree to the experimental data
of the superdeformed band starting from the state at 5.213 MeV. By the
analysis of single-particle orbits, it is found that the superdeformed state
has particle-hole nature of an - configuration. One of new findings is
parity asymmetric structure with C+Si-like clustering in the
superdeformed band. We predict that C+Si molecular bands may be
built above the superdeformed band due to the excitation of inter-cluster
motion. They are considered to be higher nodal states of the superdeformed
state. We also suggest negative-parity bands caused by the parity asymmetric
deformation.Comment: 13 figures, submitted to Phys. Rev.
Axial vector tetraquark with S=+2
Possibility of an axial vector isoscalar tetraquark with
is discussed. If the pentaquark has the
configuration, the isoscalar
(-meson) state with is expected to
exist in the mass region lower than or close to the mass of .
Within a flux-tube quark model, a possible resonant state of
is suggested to appear around 1.4 GeV with the
width MeV. We propose that the -meson is a
good candidate for the tetraquark search, which would be observed in the
decay channel.Comment: 20 pages, 5 figures, submitted to Phys.Rev.
Dipole resonances in light neutron-rich nuclei studied with time-dependent calculations of antisymmetrized molecular dynamics
In order to study isovector dipole response of neutron-rich nuclei, we have
applied a time-dependent method of antisymmetrized molecular dynamics. The
dipole resonances in Be, B and C isotopes have been investigated. In Be,
B, C, collective modes of the vibration between a core and
valence neutrons cause soft resonances at the excitation energy MeV
below the giant dipole resonance(GDR). In C, we found that a remarkable
peak at MeV corresponds to coherent motion of four valence neutrons
against a C core, while the GDR arises from the core vibration in the
MeV region. In B and C, the dipole strengths in the low
energy region decline compared with those in B and C. We also
discuss the energy weighted sum rule for the transitions.Comment: 12 figures, submitted to Phys. Rev.
New effective nuclear forces with a finite-range three-body term and their application to AMD+GCM calculations
We propose new effective inter-nucleon forces with a finite-range three-body
operator. The proposed forces are suitable for describing the nuclear structure
properties over a wide mass number region, including the saturation point of
nuclear matter. The forces are applied to microscopic calculations of
() nuclei and O isotopes with a method of antisymmetrized molecular
dynamics. We present the characteristics of the forces and discuss the
importance of the finite-range three-body term.Comment: 15 pages, 11 figures, submitted to Phys.Rev.
Structure of excited states of Be-11 studied with Antisymmetrized Molecular Dynamics
The structures of the ground and excited states of Be-11 were studied with a
microscopic method of antisymmetrized molecular dynamics. The theoretical
results reproduce the abnormal parity of the ground state and predict various
kinds of excited states. We suggest a new negative-parity band with a
well-developed clustering structure which reaches high-spin states. Focusing on
a clustering structure, we investigated structure of the ground and
excited states. We point out that molecular orbits play important roles for the
intruder ground state and the low-lying states. The features of
the breaking of clusters were also studied with the help of data for
Gamow-Teller transitions.Comment: 24 pages, 7 figures, to be submitted to Phys.Rev.
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