Penta-quark in Anisotropic Lattice QCD (original) (raw)

Pentaquark baryon in anisotropic lattice QCD

Physical Review D, 2005

The penta-quark(5Q) baryon is studied in anisotropic quenched lattice QCD with renormalized anisotropy as/at=4 for a high-precision mass measurement. The standard Wilson action at β = 5.75 and the O(a) improved Wilson quark action with κ=0.1210(0.0010)0.1240 are employed on a 12 3 ×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, mΘ = 2.25 GeV, which is much heavier than the experimentally observed Θ + (1540). The lowest negative-parity 5Q appears at mΘ = 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.

Anisotropic lattice QCD studies of penta-quarks and tetra-quarks

AIP Conference Proceedings, 2006

Anisotropic lattice QCD studies of penta-quarks(5Q) with J P = 1/2 ± and 3/2 ± are presented at the quenched level together with tetra-quarks(4Q). The standard gauge action at β = 5.75 and O(a) improved quark (clover) action with κ = 0.1410(0.010)0.1440 are employed on the anisotropic lattice with the renormalized anisotropy a s /a t = 4. The "hybrid boundary condition(HBC)" is adopted to discriminate a compact resonance state from scattering states. Only massive 5Q states are found for J P = 1/2 + and 3/2 ± , which cannot be identified as Θ + (1540). A low-lying 5Q state is found for J P = 1/2 − at m 5Q ≃ 1.75 GeV, which however turns out to be an NK scattering state through the HBC analysis. A preliminary result for 4Q states is presented suggesting an existence of a compact 4Q resonance at m 4Q ≃ 1.1 GeV in the idealized SU(4) f chiral limit.

Penta-Quark Anti-Decuplet in Anisotropic Lattice QCD

Nuclear Physics B - Proceedings Supplements, 2005

The penta-quark(5Q) Θ + (1540) is studied in anisotropic lattice QCD with renormalized anisotropy as/at = 4 for a high-precision measurement. Both the positive and the negative parity 5Q baryons 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 mΘ ≃ 2.25 GeV, which is too heavy to be identified with Θ + (1540). In the negative parity channel, the lowest energy state is found at mΘ ≃ 1.75 GeV. Although it is rather close to the empirical value, it is considered to be an NK scattering state rather than a localized resonance state.

Spin 3/2 pentaquarks in anisotropic lattice QCD

Physical Review D, 2005

A high-precision mass measurement for the pentaquark (5Q) Θ + in J P = 3/2 ± channel is performed in anisotropic quenched lattice QCD using a large number of gauge configurations as N conf = 1000. We employ the standard Wilson gauge action at β = 5.75 and the O(a) improved Wilson (clover) quark action with κ = 0.1210(0.0010)0.1240 on a 12 3 × 96 lattice with the renormalized anisotropy as as/at = 4. The Rarita-Schwinger formalism is adopted for the interpolating fields. Several types of the interpolating fields with isospin I = 0 are examined such as (a) the NK *-type, (b) the (color-)twisted NK *-type, (c) a diquark-type. The chiral extrapolation leads to only massive states, i.e., m5Q ≃ 2.1 − 2.2 GeV in J P = 3/2 − channel, and m5Q = 2.4 − 2.6 GeV in J P = 3/2 + channel. The analysis with the hybrid boundary condition(HBC) is performed to investigate whether these states are compact 5Q resonances or not. No low-lying compact 5Q resonance states are found below 2.1GeV.

Search for the pentaquark resonance signature in lattice QCD

Physical Review D, 2005

Claims concerning the possible discovery of the Θ + pentaquark, with minimal quark content uudds, have motivated our comprehensive study into possible pentaquark states using lattice QCD. We review various pentaquark interpolating fields in the literature and create a new candidate ideal for lattice QCD simulations. Using these interpolating fields we attempt to isolate a signal for a fivequark resonance. Calculations are performed using improved actions on a large 20 3 ×40 lattice in the quenched approximation. The standard lattice resonance signal of increasing attraction between baryon constituents for increasing quark mass is not observed for spin-1 2 pentaquark states. We conclude that evidence supporting the existence of a spin-1 2 pentaquark resonance does not exist in quenched QCD.

Tetra-Quark Resonances in Lattice QCD

Progress of Theoretical Physics Supplement, 2007

We study qqqq-type four-quark (4Q) systems in SU(3) c anisotropic quenched lattice QCD, using the O(a)-improved Wilson (clover) fermion at β = 5.75 on 12 3 × 96 with renormalized anisotropy a s /a t = 4. For comparison, we first investigate the lowest qq scalar meson from the connected diagram and find its large mass of about 1.32 GeV after chiral extrapolation, and thus the lowest qq scalar meson corresponds to f 0 (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 boundary 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 < m q < 2m s .

Pentaquark hadrons from lattice QCD

We study spin 1/2 isoscalar and isovector candidates in both parity channels for the recently discovered Θ + (1540) pentaquark particle in quenched lattice QCD. Our analysis takes into account all possible uncertainties, such as statistical, finite size and quenching errors when performing the chiral and continuum extrapolations and we have indications that our signal is separated from scattering states. The lowest mass that we find in the I P = 0 − channel is in complete agreement with the experimental value of the Θ + mass. On the other hand, the lowest mass state in the opposite parity I P = 0 + channel is much higher. Our findings suggests that the parity of the Θ + is negative.

Tetraquark and Pentaquark Systems in Lattice QCD

Journal of Modern Physics, 2016

Motivated by the recent experimental discoveries of multi-quark candidates, e.g., the Θ + (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 N K 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 negativeparity 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 5Q 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 V 4Q for the QQ-QQ system is also described by the OGE Coulomb plus multi-Y Ansatz, when QQ andQQ 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. * Talk presented by Fumiko Okiharu at "Quark Nuclear Physics 2005" (QNP05).

The Static Pentaquark Potential in Lattice QCD

Pentaquark 04 - Proceedings of the International Workshop, 2005

We perform the first study for the static penta-quark (5Q) potential in lattice QCD with β=6.0 and 16 3 × 32 at the quenched level. Accurate results of the 5Q potential are extracted from the 5Q Wilson loop using the smearing method, which enhances the ground-state component. The tetra-quark potential for the QQ-QQ system is also studied in lattice QCD. The multi-quark potentials are found to be well described as a sum of the one-gluon-exchange Coulomb term and the multi-Y linear confinement term based on the flux-tube picture. * The lattice QCD simulation has been done on NEC-SX5 at Osaka University.

Excited state baryon spectroscopy from lattice QCD

Physical Review D, 2011

We present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including J = 7 2 , of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of SU (6) ⊗ O(3) representations and a counting of levels that is consistent with the non-relativistic qqq constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.