30 research outputs found

### Hybrid and Conventional Baryons in the Flux-Tube and Quark Models

The status of conventional baryon flux-tubes and hybrid baryons is reviewed.
Recent surprises are that a model prediction indicates that hybrid baryons are
very weakly produced in glue-rich Psi decays, and an analysis of
electro-production data concludes that the Roper resonance is not a hybrid
baryon. The baryon decay flux-tube overlap has been calculated in the flux-tube
model, and is discussed here. The behavior of the overlap follows naive
expectations.Comment: Invited plenary talk presented at the 10th International Symposium on
Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2004), 29 August
- 4 September, Beijing, China. LaTeX, 11 (encapsulated) postscript figures, 6
page

### Lattice QCD Study for the Interquark Force in Three-Quark and Multi-Quark Systems

We study the three-quark and multi-quark potentials in SU(3) lattice QCD.
From the accurate calculation for more than 300 different patterns of 3Q
systems, the static ground-state 3Q potential $V_{\rm 3Q}^{\rm g.s.}$ is found
to be well described by the Coulomb plus Y-type linear potential (Y-Ansatz)
within 1%-level deviation. As a clear evidence for Y-Ansatz, Y-type flux-tube
formation is actually observed on the lattice in maximally-Abelian projected
QCD. For about 100 patterns of 3Q systems, we perform the accurate calculation
for the 1st excited-state 3Q potential $V_{\rm 3Q}^{\rm e.s.}$ by diagonalizing
the QCD Hamiltonian in the presence of three quarks, and find a large
gluonic-excitation energy $\Delta E_{\rm 3Q} \equiv V_{\rm 3Q}^{\rm
e.s.}-V_{\rm 3Q}^{\rm g.s.}$ of about 1 GeV, which gives a physical reason of
the success of the quark model. $\Delta E_{\rm 3Q}$ is found to be reproduced
by the ``inverse Mercedes Ansatz'', which indicates a complicated bulk
excitation for the gluonic-excitation mode. We study also the tetra-quark and
the penta-quark potentials in lattice QCD, and find that they are well
described by the OGE Coulomb plus multi-Y type linear potential, which supports
the flux-tube picture even for the multi-quarks. Finally, the narrow decay
width of penta-quark baryons is discussed in terms of the QCD string theory.Comment: Invited talk at Int. Conference on Quark Confinement and the Hadron
Spectrum 6, Sardinia, Italy, 21-25 Sep 200

### Role of Large Gluonic Excitation Energy for Narrow Width of Penta-Quark Baryons in QCD String Theory

We study the narrow decay width of low-lying penta-quark baryons in the QCD
string theoryin terms of gluonic excitations. In the QCD string theory, the
penta-quark baryon decays via a gluonic-excited state of a baryon and meson
system, where a pair of Y-shaped junction and anti-junction is created. Since
lattice QCD shows that the lowest gluonic-excitation energy takes a large value
of about 1 GeV, the decay of the penta-quark baryon near the threshold is
considered as a quantum tunneling process via a highly-excited state (a
gluonic-excited state) in the QCD string theory. This mechanism strongly
suppresses the decay and leads to an extremely narrow decay width of the
penta-quark system.Comment: Talk given at International Conference on the Structure of Baryons
(Baryons 04) October 25 - 29, 2004, Ecole Polytechnique, Palaiseau, Franc

### A study of colour field distributions in the baryon

The distributions of chromo-electric and chromo-magnetic field associated
with flux tubes in the baryon are studied in SU(3) lattice QCD. Maximal Abelian
projection is used to reduce the statistical fluctuations. For a fixed source
geometry, many different string configurations are possible. We investigated
whether the string configuration, that is the choice of operator, biases the
observed flux distribution.Comment: 3 pages, 3 figures, talk given at Lattice2003(topology

### Anisotropic Lattice QCD Studies of Penta-quark Anti-decuplet

Anti-decuplet penta-quark baryon is studied with the quenched anisotropic
lattice QCD for accurate measurement of the correlator. Both the positive and
negative parity states are studied using a non-NK type interpolating field with
I=0 and J=1/2. After the chiral extrapolation, the lowest positive parity state
is found at m_{Theta} \simeq 2.25 GeV, which is too massive to be identified
with the experimentally observed Theta^+(1540). The lowest negative parity
state is found at m_{Theta}\simeq 1.75 GeV, which is rather close to the
empirical value. To confirm that this state is a compact 5Q resonance, a new
method with ``hybrid boundary condition (HBC)'' is proposed. The HBC analysis
shows that the observed state in the negative parity channel is an NK
scattering state.Comment: A talk given at International Workshop PENTAQUARK04, July 20-23, 2004
at SPring-8, Japan, 8 pages, 7 figures, 2 table

### Tetraquark and Pentaquark Systems in Lattice QCD

Motivated by the recent experimental discoveries of multi-quark candidates,
e.g., the $\Theta^+(1540)$, we study multi-quark systems in lattice QCD. First,
we perform accurate mass measurements of low-lying 5Q states with $J=1/2$ and
I=0 in both positive- and negative-parity channels in anisotropic lattice QCD.
The lowest positive-parity 5Q state is found to have a large mass of about
2.24GeV after the chiral extrapolation. To single out the compact 5Q state from
$NK$ scattering states, we develop a new method with the hybrid-boundary
condition (HBC), and find no evidence of the compact 5Q state below 1.75GeV in
the negative-parity channel. Second, we perform the first study of the
multi-quark potential in lattice QCD to clarify the inter-quark interaction in
multi-quark systems. The 5Q potential $V_{\rm 5Q}$ for the QQ-${\rm
\bar{Q}}$-QQ system is found to be well described by the ``OGE Coulomb plus
multi-Y Ansatz": the sum of the one-gluon-exchange (OGE) Coulomb term and the
multi-Y-type linear term based on the flux-tube picture. The 4Q potential
$V_{\rm 4Q}$ for the QQ-${\rm \bar{Q}\bar{Q}}$ system is also described by the
OGE Coulomb plus multi-Y Ansatz, when QQ and $\rm \bar Q \bar Q$ are well
separated. The 4Q system is described as a "two-meson" state with disconnected
flux tubes, when the nearest quark and antiquark pair is spatially close. We
observe a lattice-QCD evidence for the ``flip-flop'', i.e., the flux-tube
recombination between the connected 4Q state and the ``two-meson'' state. On
the confinement mechanism, the lattice QCD results indicate the flux-tube-type
linear confinement in multi-quark hadrons.Comment: 22 pages, 3 tables, 16 figures. Talk given at International Workshop
on Quark Nuclear Physics 2005 (QNP05), Phoenix Park, Korea, 22-24, Feb., 200

### An alternate smearing method for Wilson loops in lattice QCD

A gauge field link smearing method developed for calculations with staggered
fermions, namely the use of unitarized fat7 links, is applied to mesonic and
baryonic Wilson loop calculations. This method is found to be very effective
for reducing statistical fluctuations for large Wilson loops. Examination of
chromo-electric field distributions shows that self-interactions of the static
sources are reduced when unitarized fat7 smearing is used but long-distance
inter-quark effects are unchanged.Comment: 17 pages with 9 figures, figure and reference adde

### Four-quark stability

The physics of charm has become one of the best laboratories exposing the
limitations of the naive constituent quark model and also giving hints into a
more mature description of meson spectroscopy, beyond the simple
quark--antiquark configurations. In this talk we review some recent studies of
multiquark components in the charm sector and discuss in particular exotic and
non-exotic four-quark systems, both with pairwise and many-body forces.Comment: 6 pages. Article based on the presentations by J. Vijande and J.-M.
Richard at the Fifth Workshop on Critical Stability, Erice, Sicil

### Exploration of hyperfine interaction between constituent quarks via eta productions

In this work, the different exchange freedom, one gluon, one pion or
Goldstone boson, in constituent quark model is investigated, which is
responsible to the hyperfine interaction between constituent quarks, via the
combined analysis of the eta production processes, $\pi^{-}p\rightarrow\eta n$
and $\gamma p\rightarrow\eta p$. With the Goldstone-boson exchange, as well as
the one-gluon or one-pion exchange, both the spectrum and observables, such as,
the differential cross section and polarized beam asymmetry, are fitted to the
suggested values of Particle Data Group and the experimental data. The first
two types of exchange freedoms give acceptable description of the spectrum and
observables while the one pion exchange can not describe the observables and
spectrum simultaneously, so can be excluded. The experimental data for the two
processes considered here strongly support the mixing angles for two lowest S11
sates and D13 states as about -30 and 6 degree respectively.Comment: 7 pages, 4 figures, 4 table

### k-strings and baryon vertices in SU(N) gauge theories

It is pointed out that the sine law for the k-string tension emerges as the
critical threshold below which the spatial Z_N symmetry of the static baryon
potential is spontaneously broken. This result applies not only to SU(N) gauge
theories, but to any gauge system with stable k-strings admitting a baryon
vertex made with N sources in the fundamental representation. Some simple
examples are worked out.Comment: 4 pages, 4 figures, v2: reference added, v3: comments and references
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