| DATE: |
2004-11-11 13:30 - |
| PLACE: |
Kenkyu Honkan 3F RM321 |
| TITLE: |
Penta-quark baryon in anisotropic lattice QCD |
| CONTACT: |
tango |
| SPEAKER: |
Dr. Noriyoshi Ishii (Tokyo Inst. of Technology) |
| LANGUAGE: |
Japanese |
| ABSTRACT: |
The penta-quark(5Q) baryon is studied in anisotropic quenched lattice QCD with renormalized anisotropy a_s/a_t=4 for a high-precision mass measurement. The standard Wilson action at beta=5.75 and the O(a) improved Wilson quark action with kappa=0.1210(0.0010)0.1240 are employed on a 12^3\times 96 lattice. Contribution of excited states is suppressed by using a smeared source. We investigate both the positive- and negative-parity 5Q baryons with I=0 and spin J=1/2 using a non-NK-type interpolating field.
After chiral extrapolation, the lowest positive-parity state is found to
have a mass, m_{Theta}=2.25 GeV, which is much heavier than the
experimentally observed Theta^+(1540). The lowest negative-parity 5Q appears at m_{Theta}=1.75 GeV, which is near the s-wave NK threshold. To distinguish spatially-localized 5Q resonances from NK scattering states, we propose a new general method imposing a ``Hybrid Boundary Condition (HBC)'', where the NK threshold is artificially raised without affecting compact five-quark states. The study using the HBC method shows that the negative-parity state observed on the lattice is not a compact 5Q but an s-wave NK-scattering state. |
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