Narrow Pentaquark States in a Quark Model with Antisymmetrized Molecular Dynamics

The exotic baryon $\Theta^+(uudd\bar{s})$ is studied with microscopic calculations in a quark model by using a method of antisymmetrized molecular dynamics(AMD). We predict narrow states, $J^\pi=1/2^+(I=0)$, $J^\pi=3/2^+(I=0)$, and $J^\pi=3/2^-(I=1)$, which nearly degenerate in a low-energy region of the $uudd\bar{s}$ system. We discuss $NK$ decay widths and estimate them to be $\Gamma< 7$ for the $J^\pi=\{1/2^+,3/2^+\}$, and $\Gamma<1$ MeV for the $J^\pi=3/2^-$ 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 -- ϕ\phi mesic nuclei exist ?--

We study $\phi$-meson production in nuclei to investigate the in-medium modification of the $\phi$-meson spectral function at finite density. We consider (${\bar p},\phi$), ($\gamma,p$) and ($\pi^-,n$) reactions to produce a $\phi$-meson inside the nucleus and evaluate the effects of the medium modifications to reaction cross sections. The structures of the bound states, $\phi$-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 $\phi$.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 $ud\bar{s}\bar{s}$ is discussed. If the pentaquark $\Theta^+(1540)$ has the $(qq)_{\bar{3}}(qq)_{\bar{3}}\bar{q}$ configuration, the isoscalar $ud\bar{s}\bar{s}$($\vartheta^+$-meson) state with $J^P=1^+$ is expected to exist in the mass region lower than or close to the mass of $\Theta^+(1540)$. Within a flux-tube quark model, a possible resonant state of $ud\bar{s}\bar{s}(J^{P}=1^{+})$ is suggested to appear around 1.4 GeV with the width ${\cal{O}}(20\sim 50)$ MeV. We propose that the $\vartheta^+$-meson is a good candidate for the tetraquark search, which would be observed in the $K^+K^+\pi^-$ 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 $\beta=2.4$ on a $16^3\times 32$ 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 $3q$--structure also takes into account $(3q)(q\bar q)$--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 $0.5$ can be reproduced easily.Comment: email: [email protected], 9 pages REVTEX, 1 figure added as PostScript-file which should be stripped off before texin