Fumiko Okiharu

Study for the Pentaquark Potential in SU(3) Lattice QCD

We perform the first study of the static pentaquark (5Q) potential V(5Q) in SU(3) quenched lattice QCD with 16(3) x 32 and beta = 6.0. From the 5Q Wilson loop, V(5Q) is calculated in a gauge-invariant manner, with the smearing method to enhance the ground-state component. V(5Q) is well described by the OGE-plus-multi-Y ansatz: a sum of the one-gluon-exchange (OGE) Coulomb term and the multi-Y-type linear term proportional to the minimal total length of the flux tube linking the five quarks. Comparing with QQ and3Q potentials, we find a universality of the string tension, sigma(QQ) approximately sigma(3Q) approximately sigma(5Q), and the OGE result for Coulomb coefficients.

Tetra-Quark Resonances in Lattice QCD

q scalar meson corresponds to f0(1370). We investigate the lowest 4Q state in the spatially periodic boundary condition, and find that it is just a two-pion scattering state, as is expected. To examine spatially-localized 4Q resonances, we use the Hybrid Boundary Condition (HBC) method, where anti-periodic and periodic bound- ary conditions are imposed on quarks and antiquarks, respectively. By applying HBC on a finite-volume lattice, the threshold of the two-meson scattering state is raised up, while the mass of a compact 4Q resonance is almost unchanged. In HBC, the lowest 4Q state appears slightly below the two-meson threshold. To clarify the nature of the 4Q system, we apply the Maximum Entropy Method (MEM) for the 4Q correlator and obtain the spectral function of the 4Q system. From the combination analysis of MEM with HBC, we finally conclude that the 4Q system appears as a two-pion scattering state and there is no spatially-localized 4Q resonance in the quark-mass region of ms

A study of colour field distributions in the baryon

Abstract 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.

Tetraquark and Pentaquark Systems in Lattice QCD

We study multi-quark systems in lattice QCD. First, we revisit and summarize our 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 2.24 GeV after the chiral extrapolation. To single out the compact 5Q state from NK scattering states, we use the hybrid boundary condition (HBC), and find no evidence of the compact 5Q state below 1.75 GeV in the negative-parity channel. Second, we study the multi-quark potential in lattice QCD to clarify the inter-quark interaction in multi-quark systems. The 5Q potential V5Q for the QQ- 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 V4Q for the QQ- QQ system is also described by the OGE Coulomb plus multi-Y Ansatz, when QQ and QQ are well separated. The 4Q system is described as a “two-meson” state with disconnected flux tubes, when the nearest quark and antiquark pair are spatially close. We observe a lattice-QCD evidence for the “flip-flop”, i.e., the fluxtube 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. Finally, we propose a proper quark-model Hamiltonian based on the lattice QCD results.

Study of quark confinement in baryons with lattice QCD

In SU(3) lattice QCD, we perform the detailed study for the ground-state three-quark (3Q) potential V 3 Q g.s. and the 1st excited-state 3Q potential V 3 Q e.s. , i.e., the energies of the ground state and the 1st excited state of the gluon field in the presence of the static three quarks. From the accurate calculation for more than 300 different patterns of 3Q systems, the static ground-state 3Q potential V 3 Q 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 calculate the 1st excited-state 3Q potential V 3 Q e.s. , and find a large gluonic-excitation energy Δ E 3 Q ≡ V 3 Q e.s. − V 3 Q g.s. of about 1 GeV, which gives a physical reason of the success of the quark model even without gluonic excitations. We present also the first study for the penta-quark potential V5Q in lattice QCD, and find that V5Q is well described by the sum of the OGE Coulomb plus multi-Y type linear potential.

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 theory in terms of gluonic excitations. In the QCD string theory, penta-quark baryons decay 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 penta-quark baryons 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 low-lying penta-quark decay and leads to an extremely narrow decay width.

Lattice QCD Evidence for Exotic Tetraquark Resonance

We study the manifestly exotic tetraquark D

INTER-QUARK POTENTIALS IN BARYONS AND MULTI-QUARK SYSTEMS IN QCD

_{\rm s0}^{++}(cu\bar s \bar d)

Multi-Quarks and Two-Baryon Interaction in Lattice QCD

and the scalar tetraquark

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

f_0(ud \bar u \bar d)