108 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
Recent topics of mesic atoms and mesic nuclei -- mesic nuclei exist ?--
We study -meson production in nuclei to investigate the in-medium
modification of the -meson spectral function at finite density. We
consider (), () and () reactions to produce a
-meson inside the nucleus and evaluate the effects of the medium
modifications to reaction cross sections. The structures of the bound states,
-mesic nuclei, are also studied. For strong absorptive interaction cases,
we need to know the spectrum shape in a wide energy region to deduce the
properties of .Comment: Talk given at EXA08, Vienna, September 2008. To be published in the
Proceedings, Hyperfine Interactions. 6 pages, 6 figure
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.
A Study of Degenerate Four-quark states in SU(2) Lattice Monte Carlo
The energies of four-quark states are calculated for geometries in which the
quarks are situated on the corners of a series of tetrahedra and also for
geometries that correspond to gradually distorting these tetrahedra into a
plane. The interest in tetrahedra arises because they are composed of {\bf
three } degenerate partitions of the four quarks into two two-quark colour
singlets. This is an extension of earlier work showing that geometries with
{\bf two} degenerate partitions (e.g.\ squares) experience a large binding
energy. It is now found that even larger binding energies do not result, but
that for the tetrahedra the ground and first excited states become degenerate
in energy. The calculation is carried out using SU(2) for static quarks in the
quenched approximation with on a lattice. The
results are analysed using the correlation matrix between different euclidean
times and the implications of these results are discussed for a model based on
two-quark potentials.Comment: Original Raw PS file replace by a tarred, compressed and uuencoded PS
fil
eta-Nucleus interactions and in-medium properties of N*(1535) in chiral models
The properties of eta-nucleus interaction and their experimental consequences
are investigated with eta-nucleus optical potentials obtained by postulating
the N*(1535) dominance for eta-N system. The N*(1535) properties in nuclear
medium are evaluated by two kinds of chiral effective models based on distinct
pictures of N*(1535). We find that these two models provide qualitatively
different optical potentials of the eta meson, reflecting the in-medium
properties of N*(1535) in these models. In order to compare these models in
physical observables, we calculate spectra of (d,3He) reactions for the eta
mesic nucleus formation with various kinds of target nuclei. We show that the
(d,3He) spectra obtained in these models are significantly different and are
expected to be distinguishable in experiments.Comment: 24 pages, 8 figure
The Spin Structure of the Proton in a Non-relativistic Quark Model
The spin structure of the proton is investigated in the framework of an
extended quark potential model which in addition to the conventional
--structure also takes into account --admixtures in the
proton wave function. For reasons of parity such admixtures contain an odd
orbital angular momentum thus allowing the proton spin to be shared among quark
spins and orbital angular momenta. We show that only certain admixtures are
suited for a significant reduction of the quark spin content of the proton as
suggested by the EMC--result. Within a Hamiltonian model quark spin
contributions to the proton spin down to can be reproduced easily.Comment: email: [email protected], 9 pages REVTEX, 1
figure added as PostScript-file which should be stripped off before texin
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